Caterpillarasphalt paverasphalt screed
Caterpillar AS4251C
Maintenance schedule, common problems & OEM parts breakdown
The Caterpillar AS4251C is a double-width, hydraulic power-extendible asphalt screed - a work tool, not a standalone paver. It carries no engine, ECM or undercarriage of its own; it mounts to and draws all hydraulic power from a Cat paver tractor. Factory-documented host pairings are the AP555E (Cat C4.4 engine) and the AP655D (Cat C6.6 with ACERT Technology, 129.5 kW/174 hp gross at 2200 rpm). Standard paving range runs 2.55-5.00 m (8.4-16.4 ft), extendible with bolt-on or hydraulic power-extending frames to roughly 7.0-8.0 m (23-26 ft) depending on configuration and heat system fitted. Screed heat comes as either an LPG-fired burner system or an electric plate-heat system fed by a tractor-mounted generator, each with independent thermostatic zone control. Serial prefix DLB covers its production run. Combined tractor-and-screed operating weight on the AP655D pairing runs around 19,165 kg (42,257 lb), but that figure belongs to the host machine and screed together, not the screed alone.
What sets the AS4251C apart in Cat's screed lineup is its 400 mm (15 in) wide main and extender plates paired with dual power-extending frames, versus the narrower 330 mm (13 in) plates and electric-only heat on its AS4252C sibling - specs that look similar on paper but aren't interchangeable. In the used and parts market, the AS4251C almost always turns up still mounted to its host tractor, so identifying which paver it left the factory on (AP555E or AP655D) matters as much as the screed's own condition, since mounting and hydraulic hookups are matched to that specific tractor. Wear concentrates in a short, predictable list of places: screed plates, tamper bar components, extension slide seals, tow-arm bushings, and the heat system's igniter/regulator or electric elements. Because it has no engine or ECM to fail, a well-maintained AS4251C on a sound host tractor holds its value longer than the powertrain it's paired with, making the screed a durable long-term parts and service item even as tractors get swapped out around it.
Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.
Caterpillar AS4251C specifications
Engine
| Identity note | AS4251C is a double-width hydraulic power extendible asphalt screed, not a standalone powered paver. It has no engine of its own; it mounts on and is towed/carried by a tractor unit (documented paired with the AP655D track paver). Engine figures below are the carrier paver's engine as published for the AS4251C-equipped configuration. |
| Engine model (carrier paver) | Cat C6.6 with ACERT Technology, 6-cylinder, turbocharged, air-to-air aftercooled diesel |
| Gross power (SAE J1995) at 2200 rpm | 129.5 kW / 174 hp |
| Net power (ISO 9249) at 2200 rpm | 121.9 kW / 163.5 hp |
| Net power (EEC 80/1269) | 121.9 kW / 163.5 hp |
| Bore | 105 mm (4.13 in) |
| Stroke | 127 mm (5.0 in) |
| Displacement | 6.6 L (403 cu in) |
| Emissions tier | Meets EU Stage IIIA |
Weights
| Operating weight, paver with AS4251C screed (MTS or steel track undercarriage) | 19 165 kg (42,257 lb) — includes 75 kg operator, canopy, fuel tank at 50%, leveling system, standard-width screed (2.55-5 m) |
| Shipping weight, tractor only (no screed) | 15 050 kg (33,179 lb) |
| Shipping weight, tractor with AS4251C screed | 18 890 kg (41,645 lb) — canopy lowered, fuel tank at 10%, manual apron, standard screed end gates |
| Ground pressure | Not published in available spec sheets for this configuration |
Dimensions
| Standard paving range (AS4251C screed) | 2550-5000 mm (8.4-16.4 ft) |
| Maximum paving width with extensions | 7000-8000 mm (23-26 ft), varies by configuration/heat system/extension type |
| Screed extension options | 5.5 m, 6.5 m, 7 m, 8 m extensions available |
| Main/extender screed plate width (front to back) | 457 mm (18 in) |
| Auger diameter | 406 mm (16 in) |
| Auger adjustable range | 215 mm (8.5 in) |
| Combined machine (tractor + screed) transport length | 6160 mm (242.5 in) — length with push roller and screed; tractor-only length with push roller is 4950 mm (194.9 in) |
| Combined machine transport width with screed end gates (hopper raised) | 2720 mm (107.1 in); 2500 mm (98.4 in) without end gates |
| Tractor operating width (hopper lowered) | 3306 mm (130.2 in) |
| Track gauge width | 2200 mm (86.6 in) |
| Operating height with canopy | 3840 mm (151.2 in) |
| Transport height with canopy and fumes stack lowered | 2920 mm (114.9 in) |
| Track base | 3020 mm (118.9 in) with Mobil-trac undercarriage; 3060 mm (120.5 in) with steel track undercarriage |
| Hopper capacity (with conveyor tunnels) | 6.5 m3 (14.1 tonne) |
Performance
| Paving speed (Mobil-trac or steel track) | 0-25 m/min (0-82 ft/min) |
| Travel speed, Mobil-trac undercarriage | 14.8 km/h (9.2 mph) |
| Travel speed, steel track undercarriage | 5.3 km/h (3.3 mph) |
| Tamper and vibrator | Variable-frequency tamper and vibrators, automatically synced to paver advance on a preset ramp; adjustable start/stop ramps for mat finish. Exact Hz figures not published in available literature. |
| Screed heating | LPG or electric heating system option; electric version uses a tractor-mounted generator (belt- or hydraulic-driven, 25 kW at 60 Hz) with independent, thermostatically controlled zones for the central and each mobile plate |
| Gradeability | Not published for this configuration |
Service capacities (summary)
| Fuel tank (carrier paver) | 200-290 L (53-76.6 US gal), varies by host tractor |
| Cooling system, total (carrier paver) | 24-30 L (6.3-7.9 US gal), varies by host tractor |
| Engine oil w/filter (carrier paver) | 11-14 L (2.9-3.7 US gal), varies by host tractor |
| Hydraulic oil tank (carrier paver) | 121-218 L (32-57.6 US gal), varies by host tractor |
| Washdown spray system | 32-38 L (8.5-10 US gal), varies by host tractor |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
AS4251C fluids & capacities
| System | Capacity | Recommended fluid |
|---|---|---|
| Identity note: AS4251C screed vs. host tractor | n/a | AS4251C is the double-width hydraulic power extendible screed, not a self-powered paver. It carries no engine, no coolant system, no fuel tank and no hydraulic tank of its own — it draws hydraulic power and fluid from whichever tractor it is mounted on. Documented host pairings include the AP555E (Cat C4.4 engine) and the AP655D (Cat C6.6 ACERT engine). All capacities below are the host-tractor factory refill figures and vary by which paver the screed is fitted to. |
| Engine crankcase (with filter) | 11-14 L (2.9-3.7 US gal), varies by host tractor: AP555E (C4.4) 11 L / AP655D (C6.6 ACERT) 14 L | Cat DEO SAE 15W-40 for general service. Use Cat DEO SAE 10W-30 in ambient range -18°C to 40°C (0°F to 104°F). For extreme cold, Cat DEO-ULS Cold Weather SAE 0W-40 covers -40°C to 40°C. Meets Cat ECF-2/ECF-3 engine oil spec. |
| Cooling system (total) | 24-30 L (6.3-7.9 US gal), varies by host tractor: AP555E 24 L / AP655D 30 L | Cat ELC (Extended Life Coolant), premixed, low-silicate formula. Standard premix protects to roughly -36°C (-33°F); check freeze point on the coolant container for the exact mix ratio in service. |
| Fuel tank | 200-290 L (53-76.6 US gal), varies by host tractor: AP555E 200 L / AP655D 290 L | Standard on-highway grade diesel fuel meeting the engine's fuel specification. No special Cat-branded fuel additive is called out beyond standard diesel fuel conditioner for cold-weather gelling. |
| Diesel exhaust fluid (DEF) tank | 19 L (5 US gal) — reported for one host-tractor configuration; not confirmed across all AS4251C host pairings | API-certified DEF (32.5% urea solution) where the host tractor's engine tier requires SCR aftertreatment. Not applicable to earlier Tier 3 / Stage IIIA host engines, which use no DEF. |
| Hydraulic system and tank | 121-218 L (32-57.6 US gal), varies by host tractor: AP555E 121 L / AP655D 218 L | Cat HYDO Advanced 10 (or the 20/30 grade for warmer climates), rated for an ambient operating window of about -20°C to 40°C (-4°F to 104°F). This same tank supplies the closed-loop hydrostatic propel drive, so no separate transmission oil fill exists on this machine type. |
| Propel drive / planetary final drives (track undercarriage) | Not documented in available factory literature for this screed's host tractors — treat as a dealer-verify item | If serviced separately from the shared hydraulic system, Cat TDTO (Transmission/Drive Train Oil) or Cat GO Gear Oil 85W-140 are the general Cat-branded options for planetary final drive compartments on this class of track-type paver. Confirm exact fill and interval against the specific OMM before servicing. |
| Axles/differentials | Not applicable | Machine uses a track-type (Mobil-trac or steel track) undercarriage with hydrostatic propel, not a wheeled axle/differential arrangement. |
| Washdown spray system | 32-38 L (8.5-10 US gal), varies by host tractor: AP555E 32 L / AP655D 38 L | Water-based asphalt release/washdown solution. Not a lubricant system; no viscosity or climate grade applies. |
| Screed (AS4251C) grease points — extension, crown and tilt mechanisms | Spec only — no fill capacity listed; lubrication points are grouped at remote fittings for routine service | Cat Multipurpose Grease (Cat MPGM), or Cat Advanced 3Moly Grease at heavy-load/extreme-pressure points. No published climate-based grease grade split for this screed in available literature. |
Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.
Caterpillar AS4251C maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 10 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
| Every 2,000 h |
|
| Every 4,000 h |
|
Servicing the AS4251C beyond the schedule
Predictive Maintenance & Fluid Analysis
The AS4251C has no engine or reservoir of its own, so predictive work centers on the host tractor's hydraulic circuit that feeds it. Sample and trend the AP555E/AP655D hydraulic tank condition, since contaminated oil shows up first as screed float drift or slow extension response rather than a tractor fault. Check grease condition at extension slides, crown/tilt linkage and tow-arm pivots for abrasive grit at every service interval; gritty or discolored grease signals accelerated slide-seal wear before it becomes a visible leak.
Corrective & Common Repairs
Extension slide seals are the most common wear item, abraded by hardened asphalt dragged through the tunnel on every power-extend cycle; end-of-shift wash-down slows this failure. Tamper bar mounting hardware and wear strips loosen under vibration and need periodic torque checks and replacement. LPG heat systems commonly fault on no-ignition after idle periods, usually cleared by purging the fuel line and re-cycling ignition rather than replacing the igniter outright; electric systems more often fault at generator draw or a single dead zone sensor.
Overhaul & Rebuild Points
Screed plate wear drives most rebuild decisions: a new plate runs about 12 mm (1/2 in) thick, and uneven front-to-rear wear on one side points to a screed run out of alignment rather than normal use. Crown/leveling linkage bushings and tow-arm/pull-arm pivots wear as a set and rebuild best together, since play in any one point shifts crown and mat thickness. Extension slide rails and seals should be rebuilt as a matched set to restore consistent paving width across the full range.
Seasonal & Environment Servicing
LPG heat systems need extra warm-up time and a full ignition purge in cold weather, since fuel-line condensation and cold regulators cause most no-ignition faults after winter storage. Electric heat depends on the host tractor's generator output staying stable on cold starts; confirm draw across all zones before the first cold-weather pass. In hot, abrasive mixes, extension slides and tunnel surfaces need more frequent wash-down to stop packed mix from accelerating seal wear, and mat checks should confirm lead crown running about 3 mm (1/8 in) higher than tail crown regardless of season.
AS4251C fault codes & troubleshooting
| Code | Meaning | Likely cause | What to do |
|---|---|---|---|
| CID 0100 FMI 01 | Engine oil pressure low | Low oil level, worn oil pump, plugged filter, or failing oil pressure sensor on the host tractor's engine (C4.4 on AP555E, C6.6 ACERT on AP655D) | Shut down, check oil level and filter condition, verify sensor wiring before restart |
| CID 0110 FMI 00 | Engine coolant temperature high | Low coolant, blocked radiator/screen, failed fan drive, or thermostat fault on the tractor engine | Idle down, check coolant level and radiator airflow, inspect fan drive, do not shut down hot without cool-down |
| CID 0168 FMI 01 | System/battery voltage low | Weak battery, loose or corroded ground/charging connections, or failing alternator on the tractor | Check battery state of charge and terminals, inspect alternator output and charging harness |
| CID 0168 FMI 00 | System/battery voltage high | Voltage regulator fault or bad ground causing overcharge on the tractor's electrical system | Check charging system output and grounds, replace regulator/alternator if overcharging confirmed |
| CID 0150 | Tamper bar speed sensor fault | Damaged or misaligned tamper bar speed/proximity sensor, or a broken sensor harness on the AS4251C screed | Inspect sensor air gap and mounting, check harness continuity, recalibrate per screed setup procedure |
| CID 0151 | Tamper bar drive solenoid fault | Stuck, shorted, or open tamper drive solenoid, or wiring fault feeding it, on the AS4251C screed's hydraulic tamper circuit | Check solenoid coil resistance and connector, verify hydraulic supply to the tamper valve, replace solenoid if coil is out of spec |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
AS4251C attachments & work tools
Machine identity note
The AS4251C is a double-width, hydraulic power-extendible screed unit, not a standalone paver. It mounts to and is towed by a Cat paver tractor; factory-confirmed host tractors are the AP555E and AP655D asphalt paver tractors.
Screed extensions
Heavy-duty extender frames on both the 2.5 m (8 ft) and 3.0 m (10 ft) base screed accept bolt-on extensions for extra-wide mats. Front-mount or rear-mount hydraulic power-extending frames are also offered as an alternative to bolt-on extensions, letting the operator change paving width from the cab.
Paving width range
Standard paving range runs about 2.55 m to 5.00 m (8.4 ft to 16.4 ft); with extensions fitted the screed reaches a maximum width of roughly 7.0-8.0 m (23-26 ft), varying by configuration/series and by which extension type is fitted.
Compaction system (tamper/vibrator)
Screed plates use a variable-frequency tamper bar and vibrator arrangement for compaction, with adjustable start/stop ramping tied to paver ground speed to hold a consistent mat as the machine accelerates or slows.
Heating system options
Two factory heat packages are offered: an LPG-fired system with high-efficiency burners, electronic ignition, and thermostatic control, or an electric screed-plate heating system with touch-pad controls and faster warm-up. Each screed section has its own temperature sensor feeding an independent, automatic zone controller.
Screed plate width variant
The AS4251C uses 400 mm (15 in) wide main and extender screed plates. A related sibling unit, the AS4252C, uses narrower 330 mm (13 in) plates and is electric-heat only with an LCD operating display — a separate model, not an AS4251C option.
Mounting / coupling to tractor
The screed attaches to its host paver tractor through pull arms and leveling arms rather than a quick-attach coupler; crown, slope, and extension height are adjusted through power controls on the tractor, not through a separate work-tool coupler system.
Companion paver-side items
Auger extensions and hopper end gates are companion components on the host paver (not the screed itself) used alongside the AS4251C to match material feed width to the screed's set paving width; these are matched per job, not part of the screed's own build.
Operator/ground-crew controls and guarding
A heavy-duty, self-diagnostic screed heating control unit sits at the rear of the screed for ground-crew use, and a ventilation system is built in to cut asphalt-fume exposure for the crew working around the heated plates.
All AS4251C assemblies by section
Every catalogued assembly group for the Caterpillar AS4251C. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Controls
261-9510 Adjuster Gp-Height
| 26***10 | Adjuster Group-Height | 1 |
| 27***71 | Cover; (Lh) | 1 |
| 27***72 | Cover; (Rh) | 1 |
320-3019 Adjuster Gp-Height -Rh
| 27***71 | Cover; (Lh) | 1 |
| 27***72 | Cover; (Rh) | 1 |
| 27***74 | Box; (Lh) | 1 |
320-3021 Adjuster Gp-Height -Lh
| 27***66 | Board-Control | 1 |
| 27***65 | Connector | 8 |
| 27***54 | Box-Control | 8 |
261-9514 Adjuster Gp-Height
| 09***23 | Screw; (M3x0.5x10-mm) | 4 |
| 26***14 | Adjuster Group-Height | 1 |
| 27***59 | Cabinet | 1 |
250-3368 Adjuster Gp-Manual
| 11***18 | Clip | 1 |
| 13***00 | Clip; (Tab) | 2 |
| 13***40 | Locknut; (M8x1.25-Thd) | 1 |
242-2785 Adjuster Gp-Manual -Gate
| 09***49 | Bolt; (M8x1.25x40-mm) | 1 |
| 11***18 | Clip | 2 |
| 13***40 | Locknut; (M8x1.25-Thd) | 1 |
242-2781 Crown Gp-Power
| 24***81 | Crown Group-Power | 1 |
| 34***21 | Software Group-Machine | 1 |
| 34***22 | Service Group-Machine | 1 |
299-7235 Crown Gp-Power
| 21***99 | Clamp-Half | 2 |
| 29***35 | Crown Group-Power | 1 |
| 8T***34 | Bolt-Socket Head; (M6x1x50-mm) | 2 |
276-5635 Universal Joint Gp
| 15***70 | Kit-Connecting Plug; (2-Pin)(Engine Sensor Wiring Harness) | 1 |
| 27***35 | Universal Joint Group | 1 |
| 2U***22 | Bulb (Indicator) 24v 21w Scc | 1 |
Electrical And Starting System
288-1013 Box Gp-Control
| 10***02 | Kit-Receptacle; (2-Pin)(Engine Sensor Wiring Harness) | 1 |
| 18***35 | Pin-Connector; (16-Ga To 18-Ga) | 2 |
| 28***13 | Box Group-Control | 1 |
306-6666 Box Gp-Control
| 10***02 | Kit-Receptacle; (2-Pin)(Engine Sensor Wiring Harness) | 2 |
| 10***03 | Kit; (Receptacle) (3-Pin) (Includes Receptacle As & Wedge) | 1 |
| 10***04 | Kit-Receptacle; (4-Pin)(Start Switch) | 3 |
266-3171 Box Gp-Control -Burner
| 13***72 | Cover | 1 |
| 14***42 | Clamp | 2 |
| 23***97 | Conduit-Flexible; (16.2-mm Id)(445-cm) | 0 |
356-4233 Box Gp-Relay
| 20***75 | Clamp-Half | 2 |
| 23***95 | Conduit-Flexible; (21.9-mm Id)(3353-cm) | 0 |
| 30***64 | Harness As-Wiring; (Screed) | 2 |
353-0442 Box Gp-Relay
| 13***72 | Cover | 2 |
| 14***42 | Clamp | 4 |
| 23***95 | Conduit-Flexible; (21.9-mm Id)(3353-cm) | 0 |
307-9156 Box Gp-Relay
| 10***04 | Kit-Receptacle; (4-Pin)(Start Switch) | 1 |
| 13***88 | Gasket-Connector | 1 |
| 15***98 | Screw-Button Head; (M3x0.5x1-mm) | 4 |
295-9766 Box Gp-Relay
| 10***04 | Kit-Receptacle; (4-Pin)(Start Switch) | 1 |
| 13***88 | Gasket-Connector | 1 |
| 15***98 | Screw-Button Head; (M3x0.5x1-mm) | 4 |
307-9160 Control & Mtg Gp-Machine
| 13***72 | Cover | 3 |
| 14***42 | Clamp | 6 |
| 20***75 | Clamp-Half | 6 |
303-2133 Fastener Gp-Wiring Harness
| 24***59 | Adapter | 1 |
| 24***15 | Seal-O-Ring | 1 |
| 30***33 | Fastener Group-Wiring Harness | 1 |
320-2490 Heater Ar-Screed
| 14***75 | Elbow Group | 2 |
| 14***57 | Union Bulkhead; (Orfs) | 2 |
| 14***52 | Union As | 1 |
286-3624 Heater Ar-Screed
| 25***60 | Kit-Seal; (Hydraulic Cylinder) | 1 |
| 28***24 | Heater Ar-Screed; -Electric | 1 |
| 5W***19 | Fitting-Grease | 2 |
286-3622 Heater Ar-Screed -Lpg Heat
| 24***15 | Seal-O-Ring | 1 |
| 25***63 | Adapter | 1 |
| 28***22 | Heater Ar-Screed; -Lpg Heat | 1 |
291-3698 Lamp Gp-Signal -Rh
| 14***75 | Elbow Group | 2 |
| 14***57 | Union Bulkhead; (Orfs) | 2 |
| 14***52 | Union As | 1 |
293-5354 Lighting Gp-Roading -Lh
| 14***75 | Elbow Group | 2 |
| 14***57 | Union Bulkhead; (Orfs) | 2 |
| 14***52 | Union As | 1 |
299-7245 Motor Gp-Electric
| 14***75 | Elbow Group | 2 |
| 14***57 | Union Bulkhead; (Orfs) | 2 |
| 14***52 | Union As | 1 |
296-1288 Electronics Gp-Implement
| 23***95 | Conduit-Flexible; (21.9-mm Id)(3353-cm) | 0 |
| 29***88 | Software Group-Implement | 1 |
| 30***65 | Harness As-Wiring; (Spark Plug) | 2 |
299-7223 Wiring Gp-Crown
| 16***50 | Sleeve-Abrasion; (100-In Each) | 0 |
| 25***63 | Fitting & Mtg Group-Hydraulic; -Front, Lh Frame | 1 |
| 25***64 | Fitting & Mtg Group-Hydraulic; -Front, Rh Frame | 1 |
286-3633 Wiring Gp-Heater
| 10***05 | Plate | 4 |
| 14***45 | Connector As | 8 |
| 14***35 | Tee, -6 Orb / Orfs | 2 |
286-3632 Wiring Gp-Heater -Lpg Heat
| 14***27 | Connector Group | 1 |
| 14***35 | Connect Group; (Each Includes) | 1 |
| 14***39 | Connector As. | 1 |
307-9166 Wiring Gp-Heater
| 17***39 | Bolt-Socket Head; (M8x1.25x30-mm) | 4 |
| 24***48 | Coupling As | 1 |
| 25***55 | Motor Group-Gear; (Tamper Control) | 1 |
319-7155 Wiring Gp-Heater -Lpg Heat
| 17***39 | Bolt-Socket Head; (M8x1.25x30-mm) | 4 |
| 24***12 | Ring | 1 |
| 24***85 | Coupling | 1 |
307-9155 Wiring Gp-Heater
| 14***24 | Connector Group | 1 |
| 14***27 | Connector Group | 1 |
| 14***29 | Connector As | 1 |
312-5016 Wiring Gp-Screed
| 27***83 | Seal-O-Ring | 4 |
| 27***88 | Valve Group-Check; (Pilot Operated)(Screed Extension) | 2 |
| 29***02 | Valve Group-Solenoid | 2 |
312-5017 Wiring Gp-Screed
| 21***14 | Seal-O-Ring | 1 |
| 21***74 | Seal & Retainer As | 2 |
| 21***75 | Seal-O-Ring | 1 |
293-5341 Wiring Gp-Screed -Rh
| 29***41 | Wiring Group-Screed; -Rh | 1 |
291-3697 Wiring Gp-Screed -Lh
| 09***32 | Ring-Retaining | 1 |
| 17***39 | Bolt-Socket Head; (M8x1.25x30-mm) | 4 |
| 24***49 | Adapter Group-Motor | 1 |
289-5815 Wiring Gp-Screed
| 09***32 | Ring-Retaining | 1 |
| 17***39 | Bolt-Socket Head; (M8x1.25x30-mm) | 4 |
| 24***49 | Adapter Group-Motor | 1 |
312-5019 Wiring Gp-Screed
| 1T***43 | Ball Bearing | 2 |
| 24***43 | Plug | 1 |
| 24***63 | Shaft As-Drive | 1 |
312-5015 Wiring Gp-Screed
| 14***40 | Adapter; (Straight) (-8 Orb X -8 Orfs) | 1 |
| 14***64 | Elbow, 90°,-8 Orb /-8 Orfs | 1 |
| 25***67 | Valve Group-Bank 2; -Control | 1 |
291-3691 Wiring Gp-Screed Heater -Lpg Heat
| 1T***43 | Ball Bearing | 2 |
| 24***43 | Plug | 1 |
| 24***80 | Shaft As-Drive | 1 |
291-3689 Wiring Gp-Screed Heater -Lpg Heat
| 09***01 | Bolt-Socket Head; (M8x1.25x40-mm) | 6 |
| 1T***43 | Ball Bearing | 2 |
| 24***43 | Plug | 1 |
Electrical System
288-1014 Box Gp-Screed Control -Lh
| 25***48 | Gearbox | 1 |
| 28***14 | Box Group-Screed Control; -Lh | 1 |
| 29***39 | Motor-Electric | 1 |
286-5562 Box Gp-Screed Control -Rh
| 15***70 | Kit-Connecting Plug; (2-Pin)(Engine Sensor Wiring Harness) | 1 |
| 28***62 | Box Group-Screed Control; -Rh | 1 |
| 2U***22 | Bulb (Indicator) 24v 21w Scc | 1 |
288-6125 Box Gp-Screed Control -Lh
| 11***18 | Clip | 31 |
| 13***00 | Clip; (Tab) | 2 |
| 13***40 | Locknut; (M8x1.25-Thd) | 2 |
288-6124 Box Gp-Screed Control
| 11***18 | Clip | 6 |
| 13***89 | Clip; (Ladder) | 4 |
| 13***72 | Cover | 3 |
288-6122 Box Gp-Screed Control -Rh
| 13***00 | Clip; (Tab) | 2 |
| 13***40 | Locknut; (M8x1.25-Thd) | 2 |
| 28***70 | Lock-Cable | 2 |
274-1161 Control Gp-Burner
| 11***18 | Clip | 30 |
| 13***00 | Clip; (Tab) | 3 |
| 13***40 | Locknut; (M8x1.25-Thd) | 2 |
Frame And Body
286-3634 Arm Gp-Drop
| 28***34 | Arm Group-Drop | 1 |
295-2143 Cover Gp-Access
| 12***64 | Receptacle As-Connector; (1-Pin) | 2 |
| 27***35 | Clamp | 22 |
| 28***11 | Blade; (Main, Lh) | 1 |
295-2114 Cover Gp-Access
| 09***76 | Nut; (M14x2-Thd) | 8 |
| 11***50 | Screw-Flat Head; (M8x1.25x60-mm)(M8x1.25 Thd) | 22 |
| 13***40 | Locknut; (M8x1.25-Thd) | 2 |
286-3493 Cover Gp-Screed
| 24***49 | Breather; (Hydraulic Cylinder) | 1 |
| 24***88 | Seal; (100x112x12-mm) | 1 |
| 24***89 | Seal; (140x155x16-mm) | 1 |
250-3366 Deflector Gp
| 14***80 | Pin | 2 |
| 25***66 | Deflector Group | 1 |
| 26***41 | Wall As | 1 |
339-1628 Extension Gp-Main Frame
| 14***80 | Pin | 2 |
| 26***43 | Tube As | 1 |
| 26***44 | Wall As | 1 |
339-1636 Extension Gp-Main Frame
| 26***41 | Wall As | 1 |
| 33***36 | Extension Group-Main Frame | 1 |
| 33***85 | Tube As | 1 |
265-6509 Fitting Gp-Grease
| 26***09 | Fitting Group-Grease | 1 |
| 26***44 | Wall As | 1 |
| 33***85 | Tube As | 1 |
339-1642 Frame Gp-Screed
| 33***42 | Frame Group-Screed | 1 |
286-3490 Frame Gp-Screed -Lh
| 26***96 | Film-Warning; (Fire Hazard, Read Omm) | 2 |
| 26***96 | Film-Warning; (Hot Surface) | 4 |
| 28***90 | Frame Group-Screed; -Lh | 1 |
286-3492 Frame Gp-Screed -Lh
| 22***54 | Film-Warning; (Universal, Read Omm, Intl) | 1 |
| 28***92 | Frame Group-Screed; -Lh | 1 |
| 29***22 | Film-Danger; (Shock, Electrocution Hazard) | 7 |
286-3491 Frame Gp-Screed -Rh
| 18***68 | Plate-Serial Number | 1 |
| 1P***07 | Film-Symbol; 2 On Bottom Of Upper Frame Below Engine. 2 On Front Of Upper Frame Above Boom Articulation | 2 |
| 22***54 | Film-Warning; (Universal, Read Omm, Intl) | 1 |
292-8813 Frame Gp-Sliding -Lh
| 29***13 | Frame Group-Sliding; -Lh | 1 |
292-8814 Frame Gp-Sliding -Rh
| 29***14 | Locking Tab, Frame Group-Sliding; -Rh | 1 |
311-4480 Gate Gp-End -Folding
| 31***80 | Gate Group-End; -Folding | 1 |
311-4470 Gate Gp-End
| 31***70 | Gate Group-End | 1 |
265-6510 Lines Gp-Grease
| 26***10 | Lines Group-Grease | 1 |
250-3370 Lines Gp-Grease
| 25***70 | Lines Group-Grease | 1 |
251-0819 Plate Gp-Screed -Gas
| 25***19 | Plate Group-Screed; -Gas | 1 |
310-9817 Plate Gp-Screed -Lh
| 31***17 | Plate Group-Screed; -Lh | 1 |
310-9816 Plate Gp-Screed -Rh
| 31***16 | Plate Group-Screed; -Rh | 1 |
251-0834 Plate Gp-Screed -Sliding
| 25***34 | Plate Group-Screed; -Sliding | 1 |
287-0269 Plate Gp-Screed
| 28***69 | Plate Group-Screed | 1 |
Fuel System
339-1609 Burner Gp
| 20***55 | Nut; (M20x1.5-Thd) | 2 |
| 24***20 | Nut; (M20x1.5-Thd, Lh) | 2 |
| 24***62 | Gear As; (15-Teeth) | 2 |
299-7255 Burner Gp
| 24***58 | Plate-Gauge | 4 |
| 29***55 | Burner Group | 1 |
| 32***19 | Adjuster Group-Height; -Rh | 2 |
268-6140 Fitting Gp-Fuel Lines
| 10***41 | Locknut-Bearing; (M30x1.5-Thd) | 4 |
| 17***35 | Ring-Retaining | 2 |
| 24***10 | Stopper-Rubber | 1 |
339-1638 Lines Gp-Burner
| 08***34 | Screw-Button Head | 4 |
| 09***66 | Washer; (Hard) (4.5x9x1mm Thk) | 4 |
| 16***65 | Bolt-Socket Head; (M4x0.7x16-mm) | 4 |
339-1618 Lines Gp-Burner
| 08***34 | Screw-Button Head | 4 |
| 09***66 | Washer; (Hard) (4.5x9x1mm Thk) | 4 |
| 10***02 | Kit-Receptacle; (2-Pin)(Engine Sensor Wiring Harness) | 1 |
339-1631 Lines Gp-Burner
| 27***71 | Cover; (Lh) | 1 |
| 27***72 | Cover; (Rh) | 1 |
| 27***74 | Box; (Lh) | 1 |
286-3631 Lines Gp-Burner
| 08***34 | Screw-Button Head | 4 |
| 09***66 | Washer; (Hard) (4.5x9x1mm Thk) | 4 |
| 10***02 | Kit-Receptacle; (2-Pin)(Engine Sensor Wiring Harness) | 1 |
Hydraulic System
242-2749 Adapter Gp-Motor
| 1T***43 | Ball Bearing | 2 |
| 24***43 | Plug | 1 |
| 24***80 | Shaft As-Drive | 1 |
258-7161 Adapter Gp-Motor
| 09***67 | Setscrew-Socket; (M10x1.5-Thd) | 2 |
| 24***05 | Shaft Group-Vibratory | 1 |
| 24***36 | Key-Rectangular; (Square) | 2 |
251-0781 Cylinder Gp-Hydraulic
| 09***67 | Setscrew-Socket; (M10x1.5-Thd) | 2 |
| 24***05 | Shaft Group-Vibratory | 1 |
| 25***81 | Cylinder Group-Hydraulic; -Extender | 1 |
258-7194 Fitting & Mtg Gp-Hydraulic -Rear, Lh Frame
| 09***49 | Bolt; (M8x1.25x40-mm) | 14 |
| 13***40 | Locknut; (M8x1.25-Thd) | 6 |
| 23***06 | Bumper | 1 |
258-4664 Fitting & Mtg Gp-Hydraulic -Front, Rh Frame
| 25***64 | Fitting & Mtg Group-Hydraulic; -Front, Rh Frame | 1 |
| 28***93 | Cover Group-Screed | 1 |
| 31***00 | Platform Group-Operator; -Slide | 1 |
258-7190 Fitting & Mtg Gp-Hydraulic -Rear, Rh Frame
| 22***36 | Bolt; (M24x2x85-mm) | 2 |
| 25***53 | Washer; (25x55x8-mm Thk) | 2 |
| 25***90 | Fitting & Mtg Group-Hydraulic; -Rear, Rh Frame | 1 |
258-4663 Fitting & Mtg Gp-Hydraulic -Front, Lh Frame
| 17***11 | Locknut; (M16x2-Thd) | 4 |
| 24***09 | Damper | 8 |
| 25***38 | Pad | 4 |
286-3620 Hydraulic Ar
| 09***85 | Locknut; (M16x2-Thd) | 8 |
| 15***49 | Screw-Flat Head; (M10x1.5x25-mm) | 28 |
| 19***84 | Locknut; (M10x1.5-Thd) | 28 |
286-3635 Lines Gp-Connecting
| 27***27 | Fitting-Grease | 4 |
| 28***35 | Lines Group-Connecting | 1 |
| 5W***17 | Fitting-Grease | 12 |
286-3629 Lines Gp-Extender
| 09***59 | Pin-Cotter | 4 |
| 09***19 | Ring-Retaining | 8 |
| 09***66 | Washer; (Hard) (4.5x9x1mm Thk) | 4 |
286-3627 Lines Gp-Tamper
| 10***06 | Plate As | 3 |
| 15***86 | Plate As | 2 |
| 17***08 | Plate As | 2 |
265-7799 Lines Gp-Vibratory
| 15***86 | Plate As | 1 |
| 17***08 | Plate As | 3 |
| 26***99 | Lines Group-Vibratory | 1 |
286-3628 Lines Gp-Vibratory
| 17***08 | Plate As | 1 |
| 25***34 | Plate Group-Screed; -Sliding | 1 |
| 25***78 | Pin | 2 |
286-3630 Manifold Gp-Control -Screed
| 27***22 | Bushing | 2 |
| 28***30 | Manifold Group-Control; -Screed | 1 |
| 32***50 | Plate Group-Slide | 1 |
258-7185 Motor & Mtg Gp-Tamper -Vibratory
| 25***85 | Motor & Mtg Group-Tamper; -Vibratory | 1 |
| 27***22 | Bushing | 2 |
| 32***50 | Plate Group-Slide | 1 |
258-7186 Motor & Mtg Gp-Tamper
| 12***80 | Locknut; (M12x1.75-Thd) | 2 |
| 13***40 | Locknut; (M8x1.25-Thd) | 4 |
| 17***11 | Locknut; (M16x2-Thd) | 4 |
258-7162 Motor & Mtg Gp-Tamper -Vibratory
| 17***08 | Plate As | 1 |
| 25***34 | Plate Group-Screed; -Sliding | 1 |
| 25***78 | Pin | 2 |
263-5148 Motor & Mtg Gp-Vibratory -Screed
| 08***07 | Pin | 2 |
| 09***79 | Setscrew-Socket | 4 |
| 09***76 | Nut; (M14x2-Thd) | 2 |
258-7158 Motor Gp-Gear -Tamper Control
| 24***87 | Connector | 16 |
| 25***58 | Motor Group-Gear; -Tamper Control | 1 |
| 26***34 | Hose As-Grease | 10 |
256-2539 Valve & Mtg Gp-Control -Screed Extension
| 24***87 | Connector | 40 |
| 25***39 | Valve & Mtg Group-Control; -Screed Extension | 1 |
| 31***45 | Hose As-Grease | 1 |
252-9467 Valve Gp-Bank 2 -Control
| 24***93 | Stud; (M12x1.75x100-mm) | 48 |
| 24***97 | Nut-Brass; (M12x1.75-Thd) | 96 |
| 24***04 | Nut-Brass; (M14x2-Thd) | 16 |
294-0802 Valve Gp-Solenoid
| 25***32 | Pad | 2 |
| 25***77 | Support As | 1 |
| 29***02 | Valve Group-Solenoid | 1 |
242-2753 Vibratory Gp -Rear, Rh
| 24***53 | Vibratory Group; -Rear, Rh | 1 |
| 28***33 | Wiring Group-Heater | 1 |
| 28***69 | Plate Group-Screed | 1 |
263-2536 Vibratory Gp -Hydraulic
| 09***41 | Ring-Retaining | 1 |
| 24***49 | Breather; (Hydraulic Cylinder) | 1 |
| 24***06 | Shaft As | 1 |
265-0684 Vibratory Gp
| 09***41 | Ring-Retaining | 1 |
| 24***49 | Breather; (Hydraulic Cylinder) | 1 |
| 24***07 | Shaft As | 1 |
242-2751 Vibratory Gp -Front, Rh
| 24***51 | Vibratory Group; -Front, Rh | 1 |
| 25***71 | Bar-Tamper; (Main, Rh) | 1 |
| 25***72 | Bar-Tamper; (Main, Lh) | 1 |
242-2752 Vibratory Gp -Rear, Lh
| 24***52 | Vibratory Group; -Rear, Lh | 1 |
| 25***70 | Bar Group-Tamper | 1 |
| 25***19 | Plate Group-Screed; -Gas | 1 |
242-2750 Vibratory Gp -Front, Lh
| 10***02 | Kit-Receptacle; (2-Pin)(Engine Sensor Wiring Harness) | 1 |
| 12***64 | Receptacle As-Connector; (1-Pin) | 2 |
| 18***35 | Pin-Connector; (16-Ga To 18-Ga) | 2 |
265-8847 Vibratory Gp
| 08***36 | Clip-Internal; (Water Temperature Regulator) | 1 |
| 24***49 | Breather; (Hydraulic Cylinder) | 1 |
| 24***09 | Shaft As | 1 |
Implements
251-0770 Bar Gp-Tamper
| 25***70 | Bar Group-Tamper | 1 |
287-2280 Blade & Heater Gp-Tamper
| 28***80 | Blade & Heater Group-Tamper | 1 |
339-1646 Blade & Heater Gp-Tamper
| 33***46 | Blade & Heater Group-Tamper | 1 |
339-1704 Extension Ar-Screed -Lpg Heat, 8-M
| 33***04 | Extension Ar-Screed; -Lpg Heat, 8-M | 1 |
339-1702 Extension Ar-Screed -Lpg
| 33***02 | Extension Ar-Screed; -Lpg | 1 |
339-1701 Extension Ar-Screed -Lpg Heat
| 33***01 | Extension Ar-Screed; -Lpg Heat | 1 |
265-0685 Housing Gp-Eccentric Weight
| 26***85 | Housing Group-Eccentric Weight | 1 |
263-5149 Housing Gp-Eccentric Weight -Main, Lh
| 26***49 | Housing Group-Eccentric Weight; -Main, Lh | 1 |
263-5151 Housing Gp-Eccentric Weight -Extension
| 26***51 | Housing Group-Eccentric Weight; -Extension | 1 |
263-5150 Housing Gp-Eccentric Weight -Main, Rh
| 26***50 | Housing Group-Eccentric Weight; -Main, Rh | 1 |
305-5869 Manifold Gp-Fuel
| 30***69 | Manifold Group-Fuel | 1 |
325-4950 Plate Gp-Slide
| 32***50 | Plate Group-Slide | 1 |
242-2677 Shaft Gp-Drive
| 24***77 | Shaft Group-Drive | 1 |
296-9357 Shaft Gp-Vibratory -Eccentric, Rh
| 29***57 | Shaft Group-Vibratory; -Eccentric, Rh | 1 |
265-6611 Shaft Gp-Vibratory
| 26***11 | Shaft Group-Vibratory | 1 |
296-9358 Shaft Gp-Vibratory -Eccentric, Lh
| 29***58 | Shaft Group-Vibratory; -Eccentric, Lh | 1 |
251-0764 Tamper Gp-Screed
| 25***64 | Tamper Group-Screed | 1 |
251-0767 Tube Gp-Extension -Telescoping
| 25***67 | Tube Group-Extension; -Telescoping | 1 |
339-9762 Tube Gp-Extension -Sliding
| 33***62 | Tube Group-Extension; -Sliding | 1 |
269-5145 Tube Gp-Extension -Sliding
| 26***45 | Tube Group-Extension; -Sliding | 1 |
340-0125 Tube Gp-Extension -Sliding
| 34***25 | Tube Group-Extension; -Sliding | 1 |
269-5142 Tube Gp-Extension -Sliding
| 26***42 | Tube Group-Extension; -Sliding | 1 |
Machine Arrangement
265-3787 Conversion Ar-Screed -Lpg Heat
| 25***66 | Deflector Group | 1 |
| 25***68 | Adjuster Group-Manual | 1 |
| 25***70 | Lines Group-Grease | 1 |
266-3172 Conversion Ar-Screed -Lpg Heat
| 24***95 | Support As | 8 |
| 24***15 | Burner | 8 |
| 24***36 | Bolt; (M12x1.75x20-mm) | 16 |
339-1633 Conversion Gp-Gas -Fuel Fired Heater
| 14***36 | Adapter; (Straight) (-6 Orb X -6 Orfs) | 1 |
| 15***50 | Elbow As | 1 |
| 26***40 | Fitting Group-Fuel Lines | 2 |
339-1624 Conversion Gp-Gas -Fuel Fired Heater
| 26***41 | Block | 1 |
| 26***47 | Washer; (13x18x1.5-mm Thk) | 4 |
| 26***48 | Washer; (17x23x1.5-mm Thk) | 1 |
339-1639 Conversion Gp-Screed -Fuel Fired Heater
| 09***60 | Setscrew-Socket; (M6x1x6-mm) | 1 |
| 11***52 | Bolt-Hex Head; (M4x0.7x10mm) | 2 |
| 17***11 | Locknut; (M16x2-Thd) | 1 |
281-6251 Screed Ar
| 09***60 | Setscrew-Socket; (M6x1x6-mm) | 1 |
| 11***52 | Bolt-Hex Head; (M4x0.7x10mm) | 2 |
| 17***11 | Locknut; (M16x2-Thd) | 1 |
339-1643 Screed Ar
| 09***60 | Setscrew-Socket; (M6x1x6-mm) | 1 |
| 17***11 | Locknut; (M16x2-Thd) | 1 |
| 21***21 | Locknut | 2 |
339-1637 Screed Ar
| 09***60 | Setscrew-Socket; (M6x1x6-mm) | 1 |
| 17***11 | Locknut; (M16x2-Thd) | 1 |
| 21***21 | Locknut | 2 |
356-8830 Special Ar-Screed
| 24***58 | Tube As | 1 |
| 24***73 | Tube As | 1 |
| 24***77 | Tube As | 1 |
356-8831 Special Ar-Screed -Folding Endgate
| 24***58 | Plate-Gauge | 4 |
| 26***10 | Adjuster Group-Height | 2 |
| 26***14 | Adjuster Group-Height | 2 |
Operator Station
286-3618 Platform Gp-Operator
| 26***43 | Manifold As-Gas | 1 |
| 26***46 | Fitting | 8 |
| 26***47 | Washer; (13x18x1.5-mm Thk) | 8 |
315-3700 Platform Gp-Operator -Slide
| 31***00 | Platform Group-Operator; -Slide | 1 |
| 32***47 | Support As | 1 |
| 32***52 | Pad | 2 |
Service Equipment And Supplies
309-1496 Plate & Film Gp
| 30***96 | Plate & Film Group | 1 |
265-6503 Plate & Film Gp
| 26***03 | Plate & Film Group | 1 |
286-3619 Plate & Film Gp
| 28***19 | Plate & Film Group | 1 |
AS4251C serial number reference
The PIN plate for the AS4251C is riveted to the screed main frame, usually near the tow-point/hitch end or on a frame rail close to the operator control station, not on the smoothing plates themselves. It reads as a 3-letter prefix (DLB) followed by a sequential unit number, e.g. DLB00123; the prefix identifies the screed's build series and the digits are the individual unit sequence, not a build date.
| Prefix | Identifies | Notes |
|---|---|---|
| DLB | AS4251C double-width hydraulic power extendible screed, DLB00001-UP | Pairs with multiple track paver tractors, not just one: AP555E (mid-range paver line refresh) and AP655D (F-Series high-production paver, C6.6 ACERT). No engine of its own; runs off the towing paver's hydraulics, with a choice of LPG burner heat or electric plate heat fed by a tractor-mounted generator. Standard paving range about 2.55-5.00 m; max width varies by configuration/extensions, roughly 7-8 m depending on heat system and end-gate setup. No plant/region split or second prefix found; treat as one continuous production run unless a dealer parts lookup shows a later change. |
Frequently asked questions
What engine does the Caterpillar AS4251C have?
The AS4251C has no engine of its own. It's a screed attachment that mounts to and draws all hydraulic power from a Cat paver tractor. Factory-documented host pairings are the AP555E, powered by a Cat C4.4, and the AP655D, powered by a Cat C6.6 with ACERT Technology (129.5 kW/174 hp gross at 2200 rpm). Any engine spec quoted for an "AS4251C" actually belongs to whichever tractor it's paired with.
What is the operating weight of the Caterpillar AS4251C?
The screed isn't published with its own standalone weight figure; Cat publishes weight for the combined tractor-and-screed package. On an AP655D fitted with the AS4251C, combined operating weight runs about 19,165 kg (42,257 lb), and shipping weight for the tractor with the screed attached is about 18,890 kg (41,645 lb). On the smaller AP555E host the combined figure runs lower. Check the spec sheet for the exact host tractor pairing for a precise number.
What replaced the Caterpillar AS4251C?
No documented direct successor exists for the AS4251C. It remains part of Cat's current screed lineup alongside its narrower-plate, electric-only sibling the AS4252C, and continues to be offered on the AP555E and AP655D paver tractors. If matching a used unit to parts or a rebuild kit, confirm the exact host tractor pairing and serial prefix (DLB) with your dealer rather than assuming a newer screed model is a drop-in replacement.
What AS4251C owners discuss
What hydraulic issues show up on the AS4251C's extension and tamper circuits?
Extension slide seals are the first wear point. Packed asphalt dragged in and out of the main frame during power-extend cycles abrades the slide seals, and the fix crews report is simple: scrape and wash down the tunnel, gates, and extension rails at the end of every shift so hardened mix stops chewing the seals on the next cycle. When the screed is set to float, lift cylinders should hold zero pressure top and bottom; a screed that settles on its own, or lifts unevenly side to side, points to low or contaminated hydraulic fluid first, then worn cylinder packings if fluid checks out clean. Tow point and pivot bushings are wear items too and show up as slop that changes crown and mat thickness before it ever looks like a hydraulic fault. Because the screed has no pump or reservoir of its own, all of this runs off the host tractor's hydraulic system (AP555E or AP655D), so oil condition on the tractor side matters as much as the screed hardware. Have your dealer verify cylinder and seal wear before committing to a rebuild.
LPG or electric heat on the AS4251C - which is the better system to own?
Both are used across this screed's production and neither one is a bad choice, but the tradeoffs are consistent. LPG burners give even plate heat once the regulator and igniter are dialed in, but they carry more upkeep: igniters, regulators, and burner tips age and eventually need replacing, and a no-ignition fault after the screed sits idle is a common complaint that's usually cleared by purging the fuel line and re-cycling ignition a few times rather than replacing parts. Electric heat is the direction newer screeds are trending because it heats plates more evenly and cuts down on warping compared to fuel-fired elements, but it depends on the host tractor supplying enough generator capacity - not every paver in the field is set up for it. Whichever system is fitted, an inconsistent mat at the start of a run is usually a warm-up problem, not a heater fault: give the plates full time to reach operating temperature before material contact.
How much wear should I expect in the leveling arms, tow points, and crown adjustment?
Tow point and pull-arm pivots are wear points by design and the amount of play is the tell. A small amount of slop in these bushings changes crown and mat thickness more than it looks like it should, so they get checked routinely rather than only when a problem shows up. Standard crown setup calls for the lead (front) crown to run about 3 mm (1/8 in) higher than the tail crown; getting this wrong is a common cause of an open, streaky stripe down the center of the mat. Extender height needs to match the main screed exactly - if it's off, transition marks appear in the mat at the extension joint. None of this is undercarriage-related; it's screed geometry and linkage wear, and it's checked with stringlines across the rear and front edges, not with a torque wrench.
Grade and slope sensors act erratic on the screed - is the sensor bad?
Usually not. The sensor itself is rarely the failure point; mounting and wiring are. Sensor position relative to the auger shaft centerline sets reaction time (ahead of center for profile/joint matching, behind the tow point for smoothness), and a sensor that's been knocked out of position by material buildup or vibration will chase grade even though it's functioning correctly. Loose connectors and chafed harness runs near the auger tunnel are the next most common cause of dropouts, checked through the system's sensor connectivity diagnostic before any sensor gets replaced. Because this screed has no engine ECM of its own, any fault codes trace back to the host tractor's grade-control controller, not a screed-resident module. Have your dealer verify sensor alignment and wiring continuity before swapping a sensor.
Does the AS4251C behave differently on an AP555E versus an AP655D?
The screed itself is identical; what changes is how much reserve the host tractor has to feed it. The AP555E runs a Cat C4.4 engine and the AP655D runs a larger Cat C6.6 ACERT, so on wide, fully extended passes the AP655D pairing has more hydraulic flow and power margin in reserve for the extension, tamper, and vibrator loads simultaneously. On an AP555E pushing maximum width with LPG or electric heat also drawing power, some operators report the combination working harder to keep up on tougher mixes. Neither pairing is wrong - both are factory-documented setups - but if the job is consistently wide-width, heavy-mix paving, the AP655D combination has more headroom.
What should I check before buying a used AS4251C?
Start with the screed plates: measure thickness at all four corners, front and rear. A new plate runs about 12 mm (1/2 in); if you're still seeing roughly 6 mm (1/4 in) there's reasonable life left. If front and rear thickness differs a lot on the same side, the previous owner ran the screed nose-heavy and out of alignment - budget for plate replacement. Check welds and mounting bolts with a flashlight for cracks and looseness, and check tow point and pivot bushings by hand for play. Run every hydraulic function - extension in and out, tamper, vibrator, main lift - and confirm smooth, responsive movement with no drift in float. Test the heat system fully (LPG ignition cycle, or electric elements and generator draw if electric) since this is the single most common deferred-maintenance item on used screeds. Finally confirm which tractor it's coming off - AP555E or AP655D - since mounting and hydraulic hookups are matched to the specific host, and verify the pairing and hour meter data with your dealer before final price.
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
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