Komatsu 3D78AE-3B(S/N 00101-UP)
Maintenance schedule, common problems & OEM parts breakdown
The Komatsu 3D78AE-3B (S/N 00101-UP) is a compact crawler excavator engineered for utility and municipal work. It belongs to the PC27R-8 and PC35R-8 family, featuring a 3-cylinder, 2.4-liter diesel engine producing 196 hp. The machine operates in the 18,000 to 20,000 lb weight class, suitable for tight access jobsites. Production years span the late 2000s through the early 2010s. It succeeded the PC27MR-3 series and was eventually replaced by the PC27MR-5 and PC30MR-5 models. Configurations offered include standard and deluxe cab options, varying stick lengths, and regional emissions packages.
Across the 3D78AE series, the primary change was the transition from Tier 3 to Tier 4 Interim emissions standards, requiring the addition of a Diesel Oxidation Catalyst (DOC) and upgraded fuel injection systems. The 3B variant specifically denotes the Tier 4 Interim configuration starting at serial 00101. This machine remains critical in the used market because its compact footprint and Tier 4 compliance allow it to operate in restricted urban environments where older Tier 3 machines are now restricted. Its simple 3-cylinder architecture keeps parts costs low compared to larger 4-cylinder competitors, sustaining high demand for serviceable units.
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.
Komatsu 3D78AE-3B(S/N 00101-UP) specifications
Engine
| Model | 3D78AE-3B |
| Series/Generation | 78 Series |
| Cylinders | 3 |
| Displacement | 1.2 L (73.5 cu. in.) |
| Gross Power | 19.9 kW (26.7 HP) @ 2600 rpm |
| Net Power | 17.4 kW (23.3 HP) @ 2600 rpm |
| Emissions Tier | Tier 4 Final / EU Stage V |
Weights
| Operating Weight | varies by configuration/series |
| Shipping Weight | not documented for this exact serial range — verify with your dealer |
| Ground Pressure | not documented for this exact serial range — verify with your dealer |
Dimensions
| Transport Length | not documented for this exact serial range — verify with your dealer |
| Transport Width | not documented for this exact serial range — verify with your dealer |
| Transport Height | not documented for this exact serial range — verify with your dealer |
| Track Gauge | not documented for this exact serial range — verify with your dealer |
| Ground Clearance | not documented for this exact serial range — verify with your dealer |
Performance
| Travel Speed | not documented for this exact serial range — verify with your dealer |
| Gradeability | not documented for this exact serial range — verify with your dealer |
| Dig Depth | not documented for this exact serial range — verify with your dealer |
| Bucket Capacity | not documented for this exact serial range — verify with your dealer |
Service Capacities (summary)
| Fuel Tank | not documented for this exact serial range — verify with your dealer |
| Hydraulic System | not documented for this exact serial range — verify with your dealer |
| Engine Oil | not documented for this exact serial range — verify with your dealer |
| Cooling System | not documented for this exact serial range — verify with your dealer |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
Komatsu 3D78AE-3B(S/N 00101-UP) maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 10 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
| Every 2,000 h |
|
Servicing the 3D78AE-3B(S/N 00101-UP) beyond the schedule
Predictive Maintenance & Fluid Analysis
Utilize KOWA fluid analysis at every 500-hour interval to monitor engine wear metals and hydraulic contamination. Check coolant SCA levels at 500 hours to prevent liner cavitation in the 3D78AE-3B block. Monitor DEF consumption rates to detect SCR system faults early. Inspect the air filter restriction indicator daily; clogged filters cause excessive soot accumulation in the DOC. Verify hydraulic oil viscosity and water content during 1,000-hour services to protect the main pump and valve bank.
Corrective & Common Repairs
Address frequent hydraulic hose leaks at the boom and stick joints by inspecting clamps and fittings during 250-hour checks. Replace the fuel water separator element at 500 hours to prevent injector damage from water ingress. Check the turbocharger shaft play and inspect the exhaust manifold for cracks during 1,000-hour services. Replace worn track rollers and idlers when undercarriage wear measurements exceed factory limits to maintain proper track tension and prevent derailment on steep grades.
Overhaul & Rebuild Points
Plan for major engine overhaul around 10,000 to 12,000 hours, focusing on piston ring replacement and cylinder liner inspection. Inspect the crankshaft main bearings for wear during 5,000-hour intervals. Rebuild the hydraulic main pump and swing motor when pressure tests show a 10% drop from factory specifications. Replace the final drive planetary gears and seals at 8,000 hours or when oil analysis indicates high gear wear metals. Inspect the swing circle bolts and bearing for pitting during 2,000-hour structural checks.
Seasonal & Environment Servicing
In cold climates, drain the water separator daily and use low-temperature fuel additives to prevent waxing. Check the coolant freeze point before winter to prevent block cracking. In dusty environments, clean the radiator and oil cooler fins daily to prevent overheating. Inspect the air filter pre-cleaner and outer element more frequently in high-dust conditions. Grease all pivot points daily in wet or sandy conditions to wash out contaminants. Verify battery hold-down and terminal tightness in high-vibration applications.
3D78AE-3B(S/N 00101-UP) common service parts
| Part number | Part | Notes | |
|---|---|---|---|
| YM119833-55620 | Fuel Filter Ass'Y | Fuel system service | Check fitment → |
| YM102103-55520 | O-Ring,(For Fuel Filter) | Fuel system service | Check fitment → |
| YM171051-92760 | Wrench,Fuel Filter? Water Separator | Fuel system service | Check fitment → |
| YM119810-35300 | Intake Oil Filter | Lubrication service | Check fitment → |
| YM119640-92750 | Wrench,Oil Filter? (Pc38uu) | Lubrication service | Check fitment → |
Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.
3D78AE-3B(S/N 00101-UP) fault codes & troubleshooting
| Code | Meaning | Likely cause | What to do |
|---|---|---|---|
| CA115 | Engine crankshaft speed sensor failure | Broken sensor, wiring issue, or connector corrosion | Replace the speed sensor and verify voltage at the pin connector |
| CA111 | Internal engine controller fault | ECM hardware failure | Replace or reprogram the ECM |
| CA451 | Common rail pressure sensor feedback value too high | Malfunction in the rail sensor or actual overpressure condition | Diagnose the fuel rail pressure sensor or pump lines |
| CA441 | Battery voltage too low | Weak battery or charging system failure | Replace the alternator or battery; check the voltage regulator |
| CA442 | Battery voltage too high | Alternator overcharging or regulator failure | Replace the alternator or battery; check the voltage regulator |
| CA122 | Intake air pressure high voltage | Sensor malfunction or wiring issue | Verify the intake pressure sensor and wiring |
| CA123 | Intake air pressure low voltage | Sensor short or airflow restriction | Check for a sensor short or an airflow restriction |
| CA153 | Intake air temperature sensor error (high) | Sensor failure | Replace or test the IAT sensor |
| CA154 | Intake air temperature sensor error (low) | Sensor failure | Replace or test the IAT sensor |
| CA234 | Engine overspeed | Throttle calibration error, engine load cycle issue, or operator misuse | Verify throttle calibration, engine load cycle, or operator misuse |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
3D78AE-3B(S/N 00101-UP) attachments & work tools
Excavator Buckets
Standard and heavy-duty digging buckets are the primary work tool for this engine class, typically sized between 0.08 and 0.15 cubic meters (0.10 to 0.20 cubic yards). Factory configurations often include side-cutting blades and reinforced wear packages for high-abrasion applications.
Hydraulic Breakers
Pneumatically or hydraulically operated rock breakers are offered for demolition and quarry work, requiring specific high-flow hydraulic kits. Mounting systems utilize standard excavator quick couplers with reinforced carrier brackets to handle impact loads.
Hydraulic Hammers
Hydraulic hammers provide higher energy output than pneumatic breakers for dense material, utilizing the machine's main hydraulic circuit. Compatibility requires specific hose arrangements and flow control valves to prevent pressure spikes during operation.
Grapples and Thimbles
Multi-tilt grapples and sorting thimbles are available for material handling and recycling applications, mounted via quick coupler systems. These tools require auxiliary hydraulic lines for jaw actuation and often feature additional guarding for debris protection.
Augers and Drilling Rigs
Rotary augers and vertical drilling attachments are used for foundation and post-hole work, driven by the machine's hydraulic power. These configurations require high-torque hydraulic motors and specific mounting adapters to interface with the boom and stick assembly.
All 3D78AE-3B(S/N 00101-UP) assemblies by section
Every catalogued assembly group for the Komatsu 3D78AE-3B(S/N 00101-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Accessory
Komatsu : 3d78ae-3b(S/N 00101-Up) : Accessory : P.P.C. Pump And Mounting
| YM***70 | Pin | 2 |
| YM***02 | Screw | 3 |
| YM***20 | Clip | 1 |
Cooling System
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cooling System : Water Pump And Cooling Fan
Cylinder Block
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cylinder Block : Camshaft And Tappet
| YM***01 | Gear Ass'Y,Camshaft | 1 |
| YM***00 | Rod,Push | 6 |
| YM***50 | Bearing, Thrust | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cylinder Block : Crankshaft
| YM***00 | Gear,Crank | 1 |
| YM***80 | Parallel Pin | 1 |
| YM***50 | Pulley,Crank | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cylinder Block : Cylinder Block
| YM***00 | O-Ring (Kit) | 2 |
| YM***30 | Thrust Metal Ass'Y (Std) | 2 |
| YM***20 | Plug,Drain(Without Oil Cooler Type) | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cylinder Block : Flywheel And Flywheel Housing
| YM***50 | Oil Seal Case, Assembly | 1 |
| YM***80 | Seal? Rear | 1 |
| YM***02 | Screw | 6 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cylinder Block : Front Cover And Gear
| YM***90 | Front Cover Ass'Y | 1 |
| YM***51 | Cap, Lub. Oil Supply | 1 |
| YM***52 | Bolt | 4 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cylinder Block : Oil Pan
| YM***30 | Hose,Drain | 1 |
| YM***00 | Gasket | 2 |
| YM***00 | Bolt,Joint | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cylinder Block : Piston And Connecting Rod
| YM***50 | Ring Set (+0.25 mm) | 1 |
| YM***00 | Connecting Rod, Assembly | 3 |
| YM***00 | Screw | 2 |
Cylinder Head
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cylinder Head : Air Cleaner And Mounting
| YM***41 | Buffle | 1 |
| YM***10 | Support | 1 |
| YM***70 | Seat,Rubber | 2 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cylinder Head : Air Intake Manifold And Connection
| YM***01 | Heater,Intake Air | 1 |
| YM***52 | Screw | 4 |
| YM***00 | Clamp | 2 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cylinder Head : Cylinder Head
| YM***80 | Retainer, Spring | 6 |
| YM***00 | Guide,Valve? Exhaust | 6 |
| YM***00 | Plug | 2 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cylinder Head : Cylinder Head Cover
| YM***20 | Cover, Breather | 1 |
| YM***50 | Cover Ass'Y,Head | 1 |
| YM***51 | Cap, Lub. Oil Supply | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cylinder Head : Exhaust Manifold And Muffler
| YM***62 | Bolt | 2 |
| YM***02 | Stud | 1 |
| YM***80 | Collar | 2 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Cylinder Head : Rocker Arm
| YM***50 | Rocker Arm Ass'Y | 6 |
| YM***02 | Screw | 6 |
| YM***80 | Spring | 3 |
Electrical System
Komatsu : 3d78ae-3b(S/N 00101-Up) : Electrical System : Alternator (40a)
| YM***50 | Brush Ass'Y | 1 |
| YM***00 | Retainer,Bearing | 1 |
| YM***70 | Diode Ass'Y | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Electrical System : Alternator And Mounting (40a)
| YM***30 | Plate,Adjust | 1 |
| YM***02 | Nut | 1 |
| YM***50 | Bolt | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Electrical System : Safety Relay? Diode And Glow Plug Timer
| YM***00 | Diode | 1 |
| YM***00 | Relay, Safety | 1 |
| YM***20 | Timer,Ribbon Heater | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Electrical System : Starting Motor (2kw)
| YM***50 | Pinion Ass'Y,Pinion | 1 |
| YM***20 | Housing,Center | 1 |
| YM***40 | Field Coil Ass'Y | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Electrical System : Starting Motor And Mounting (2kw)
| YM***52 | Bolt Plated | 2 |
| (Y***1) | Starting Motor Ass'Y,(See Fig.A6210-B0a1) | 1 |
Fuel System
Komatsu : 3d78ae-3b(S/N 00101-Up) : Fuel System : Engine Stop Motor
| YM***80 | Ring,Snap | 1 |
| YM***00 | Pin,Cotter | 1 |
| YM***10 | Bracket | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Fuel System : Fuel Filter And Piping
| YM***70 | Union | 1 |
| YM***40 | Lever | 1 |
| YM***00 | Hose | 2 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)
| YM***02 | Lever Ass'Y,Stop | 1 |
| YM***10 | Pin,Stop Lever | 1 |
| YM***00 | O-Ring (Kit) | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)
| YM***01 | Weight Assembly., Governor | 1 |
| YM***90 | Shaft,Governor Lever | 1 |
| YM***16 | Pin,Spring | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Fuel System : Fuel Injection Pump (Pump) (1/2)
| YM***50 | Kit, Shim | 1 |
| YM***10 | Plate? Caution | 1 |
| YM***50 | Cover,Side | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Fuel System : Fuel Injection Pump (Pump) (2/2)
| YM***70 | Retainer, Spring | 3 |
| YM***00 | Plunger W/Barrel | 3 |
| YM***02 | Screw | 2 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Fuel System : Fuel Injection Pump And Piping
| YM***20 | Retainer, Pipe | 1 |
| YM***60 | O-Ring,Fuel Injection Pump | 1 |
| YM***20 | Pipe,Injection? No.2 | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Fuel System : Fuel Nozzle And Spill Pipe
| YM***20 | Spring | 1 |
| YM***00 | Fuel Injection Nozzle, Assembly | 1 |
| YM***80 | Pipe | 1 |
Lubricating Oil System
Komatsu : 3d78ae-3b(S/N 00101-Up) : Lubricating Oil System : Lubricating Oil Filter
| YM***50 | Nut | 1 |
| YM***00 | Valve,Relief | 1 |
| YM***02 | Bolt Plated | 3 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Lubricating Oil System : Lubricating Oil Pump And Piping
| YM***50 | Oil Pressure Transmitter | 1 |
| YM***50 | Oil Pressure Transmitter | 1 |
| YM***02 | Seal,Ring (Kit) | 2 |
Tool And Kit
Komatsu : 3d78ae-3b(S/N 00101-Up) : Tool And Kit : Gasket Kit
| YM***60 | O-Ring,Fuel Injection Pump | 1 |
| YM***40 | O-Ring,Drain Plug | 1 |
| YM***10 | Gasket,Exhaust Manifold | 1 |
Komatsu : 3d78ae-3b(S/N 00101-Up) : Tool And Kit : Tool
| YM***60 | Wrench,Fuel Filter? Water Separator | 1 |
| YM***70 | Wrench | 1 |
| YM***20 | Wrench | 1 |
Frequently asked questions
What engine does the Komatsu 3D78AE-3B (S/N 00101-UP) use?
It uses the Komatsu 3D78AE-3B, a 3-cylinder, 2.4-liter diesel engine producing 196 hp at 2,050 rpm.
What is the operating weight of this machine?
The operating weight varies by configuration and attachments, typically ranging from 18,000 to 20,000 lbs.
What model replaced the Komatsu 3D78AE-3B series?
It was replaced by the PC27MR-5 and PC30MR-5 models in the compact excavator lineup.
What 3D78AE-3B(S/N 00101-UP) owners discuss
What are the typical powertrain and hydraulic behaviors associated with the Komatsu 3D78AE-3B engine series?
What undercarriage and wear patterns are typical for machines powered by this engine?
What are the known engine quirks and maintenance requirements for the 3D78AE-3B series?
What are the common electrical and sensor issues reported for this machine type?
What should be checked when buying a used machine with the 3D78AE-3B engine?
How does the 3D78AE-3B engine handle emissions and aftertreatment systems?
What are the fluid specifications and capacity considerations for this engine?
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
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