Komatsuengine(no series)

Komatsu 4D95S-W-1G-AS(S/N 23318-UP)

Maintenance schedule, common problems & OEM parts breakdown

The Komatsu 4D95S-W-1G-AS engine powers the GD85A and GD105A bulldozer series, a line of medium-duty crawler dozers designed for heavy earthmoving and grading tasks. Produced during the late dash-6 and early dash-7 generations (approximately 1998–2007), these machines bridge the pre-Tier 3 and Tier 3 emissions eras. The 4D95S-W-1G-AS variant specifically covers serial numbers 23318 and up, succeeding earlier 4D95S-1 builds and preceding the transition to the 4D95S-1J series. Configurations offered include standard, LGP (Low Ground Pressure), and wide-track undercarriage options to match varying soil conditions and weight distribution requirements.

Across the 4D95S-W-1G-AS generation, Komatsu refined the 95 Series engine family to meet stricter emissions standards while maintaining the robust, simple architecture that defines the brand. The shift from the 4D95S-1H/1J predecessors involved updates to fuel injection calibration and exhaust treatment to comply with Tier 3 regulations. This engine matters in the used and parts market because the GD85A/GD105A platforms remain widely deployed in municipal and agricultural sectors. Their mechanical simplicity and the availability of aftermarket rebuild kits for the 4D95S block make them a cost-effective alternative to newer, electronically complex powertrains, ensuring high demand for serviceable cores and replacement components.

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 4D95S-W-1G-AS(S/N 23318-UP) specifications

Engine

Model4D95S-W-1G-AS (S/N 23318-UP)
Configuration4-cylinder, water-cooled, direct-injection diesel engine with turbocharger and intercooler
Displacement3.26 L (198.9 cu in)
Bore95 mm (3.74 in)
Stroke115 mm (4.53 in)
Gross Power137 hp (102 kW) at 2,200 rpm
Net Power137 hp (102 kW) at 2,200 rpm
Emissions TierNot documented for this exact serial range — verify with your dealer

Weights

Operating WeightNot documented for this exact serial range — verify with your dealer
Shipping WeightNot documented for this exact serial range — verify with your dealer
Ground PressureNot documented for this exact serial range — verify with your dealer

Dimensions

Transport LengthNot documented for this exact serial range — verify with your dealer
Transport WidthNot documented for this exact serial range — verify with your dealer
Transport HeightNot documented for this exact serial range — verify with your dealer
Track GaugeNot documented for this exact serial range — verify with your dealer
Ground ClearanceNot documented for this exact serial range — verify with your dealer

Performance

Travel SpeedNot documented for this exact serial range — verify with your dealer
GradeabilityNot documented for this exact serial range — verify with your dealer

Service capacities (summary)

Engine Oil CapacityNot documented for this exact serial range — verify with your dealer
Cooling System CapacityNot documented for this exact serial range — verify with your dealer
Fuel Tank CapacityNot documented for this exact serial range — verify with your dealer
Hydraulic System CapacityNot 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 4D95S-W-1G-AS(S/N 23318-UP) maintenance schedule

Service intervalTasks
Every 10 h
  • Check engine oil level and condition
  • Check hydraulic fluid level at sight glass
  • Check coolant level and ensure cap is secure
  • Drain water from fuel separator
  • Check air filter restriction indicator
  • Inspect hydraulic hoses for cracks or leaks
Every 250 h
  • Change engine oil and filter
  • Grease all points including boom, stick, and swing bearing
  • Check fluid levels across all systems
  • Inspect belts and hoses for wear
  • Check air filter outer element
  • Perform visual walk-around inspection
Every 500 h
  • Replace fuel filter
  • Replace hydraulic return filter
  • Test battery and alternator load
  • Test coolant SCA concentration
  • Collect KOWA oil sample for analysis
  • Inspect undercarriage for wear
Every 1,000 h
  • Change final drive oil on both sides
  • Inspect turbocharger condition
  • Check valve clearance adjustments
  • Measure structural wear points
  • Replace air filter outer element if dirty
  • Inspect swing machinery oil level
Every 2,000 h
  • Change hydraulic system oil
  • Flush and replace coolant
  • Change transmission oil and filter
  • Perform comprehensive component evaluation
  • Inspect structural welds on boom and stick
  • Replace worn belts and clamps

Servicing the 4D95S-W-1G-AS(S/N 23318-UP) beyond the schedule

Predictive Maintenance & Fluid Analysis

Utilize KOWA fluid analysis at every 500-hour interval to monitor wear metals and contamination in the 4D95S-W-1G-AS engine. Track iron, copper, and lead levels in the oil to detect internal bearing or liner wear early. Analyze hydraulic fluid for ISO cleanliness codes and water content to protect the high-pressure injection pump. Coolant testing must verify SCA concentration and glycol levels to prevent corrosion in the aluminum cylinder head. Regular sampling prevents catastrophic failure by identifying trends before they cause immediate downtime.

Corrective & Common Repairs

Address common 4D95S-W-1G-AS failures by inspecting the turbocharger for shaft play and checking the air intake manifold for leaks at serial break 23318. Replace worn piston rings and liners if compression drops, noting that piston height variants (95mm vs 115mm) must be matched correctly to avoid performance loss. Inspect the fuel injection pump for leakage and verify injector spray patterns. Check the alternator brushes and voltage regulator for consistent 12V output. Prompt repair of hydraulic hose leaks prevents contamination of the swing bearing and final drives.

Overhaul & Rebuild Points

Plan the inframe overhaul for the 4D95S-W-1G-AS engine around the 10,000-hour mark or when compression drops below specification. Replace cylinder liners, pistons, and rings as a set to ensure proper clearance. Inspect crankshaft journals for scoring and replace main and rod bearings if wear exceeds limits. Recondition the cylinder head by skimming the surface and replacing valve guides and seats. Verify turbocharger housing for cracks and replace intercooler core if airflow is restricted. Use a complete overhaul kit to ensure all gaskets and seals are renewed.

Seasonal & Environment Servicing

In cold climates, verify the coolant mixture provides adequate freeze protection for the 4D95S-W-1G-AS engine block. Use low-viscosity engine oil to ensure proper flow during cold starts. In dusty environments, service the air cleaner more frequently and check the restriction indicator daily to prevent abrasive wear. In high-temperature conditions, clean radiator and oil cooler fins to maintain operating temperatures. Inspect the battery for electrolyte levels and charge status, as extreme temperatures accelerate discharge. Adjust track tension to prevent excessive undercarriage wear in muddy or rocky terrain.

4D95S-W-1G-AS(S/N 23318-UP) common service parts

Part numberPart
07281-00197Clamp,(With Pre-Fuel Filter)Check fitment →
600-311-1190Plate? Caution,Fuel FilterCheck fitment →
600-311-6220Cartridge,Fuel FilterCheck fitment →
600-311-9600Fuel Filter Ass'YCheck fitment →
07000-02135O-Ring,Hydraulic Oil FilterCheck fitment →

Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.

4D95S-W-1G-AS(S/N 23318-UP) fault codes & troubleshooting

CodeMeaningLikely causeWhat to do
CA115Engine crankshaft speed sensor failureFaulty speed sensor, broken wiring harness, or corroded connector at the pin interface.Inspect the sensor wiring and connector for damage or corrosion; replace the speed sensor if voltage checks fail.
CA111Internal engine controller faultCritical internal failure of the Electronic Control Module (ECM).Replace or reprogram the ECM.
CA441Battery voltage too lowWeak battery, failing alternator, or loose connections.Check the alternator output and battery health; replace components if voltage is out of spec.
CA442Battery voltage too highFaulty voltage regulator or alternator overcharging.Replace the alternator or battery; check the voltage regulator.
CA451Common rail pressure sensor feedback value too highMalfunction in the rail pressure sensor or an actual overpressure condition in the fuel system.Diagnose the fuel rail pressure sensor and check pump lines for blockages.
AA10NXAir cleaner cloggingDirty or blocked air filter element.Replace the air filter element.
CA122Intake air pressure high voltageFaulty intake pressure sensor or restricted airflow causing high pressure readings.Verify the intake pressure sensor operation and check wiring integrity.
CA123Intake air pressure low voltageSensor short circuit or significant airflow restriction upstream.Check for a sensor short or inspect for airflow restrictions in the intake system.
CA234Engine overspeedThrottle calibration error, excessive engine load cycle, or operator misuse.Verify throttle calibration and review engine load cycles.
CA2311IMV solenoid valve failureFaulty Idle Management Valve (IMV) solenoid or open/short in the wire harness.Replace the IMV solenoid or inspect the wire harness for damage.

Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.

4D95S-W-1G-AS(S/N 23318-UP) attachments & work tools

Bulldozer Blades

The 4D95S-W-1G-AS engine is installed in Komatsu D20 and D21 series crawler dozers (specifically D20A-6, D20P-6, D20PL-6, D20Q-6, D21A-6, D21S-6, D21QG-6, and D21E-6). Typical blade configurations for this class include standard straight (SE) and semi-universal (SU) dozer blades. Capacity and width vary by specific dozer model and generation, generally ranging from 2.0 to 3.0 cubic meters for the D20 series and slightly larger for the D21 series.

Ripper Attachments

Compatible with single-shank and multi-shank rippers for the D20 and D21 dozer platforms. These are mounted to the rear frame and require auxiliary hydraulic circuits for depth control and shank adjustment. Shank configuration and penetration depth capabilities vary by the specific dozer model and ground conditions.

Coupler/Mounting Systems

Blades and rippers are mounted via factory-fitted frame brackets and pivot pins specific to the D20/D21 chassis. The engine itself is secured to the machine frame using standard mounting bolts and vibration isolators defined in the 95 Series engine service manual. No universal quick-attach couplers are used for the engine; tool mounting relies on fixed pin connections.

Hydraulic Kit Requirements

Ripper operation and any auxiliary blade functions require a factory-installed auxiliary hydraulic kit. This includes additional hydraulic lines, control valves, and connections to the main hydraulic pump. The 4D95S-W-1G-AS engine drives the hydraulic pump directly; specific pump flow rates and pressure settings are defined by the dozer model's hydraulic system design.

Factory Configurations & Guarding

Factory options for the D20/D21 dozers equipped with this engine include heavy-duty undercarriage components, wide-track shoes for low ground pressure, and various cab configurations (closed, open, or ROPS/FOPS). Engine guarding includes standard radiator screens and exhaust heat shields. Specific guarding options depend on the operating environment and regional emissions requirements.

All 4D95S-W-1G-AS(S/N 23318-UP) assemblies by section

Every catalogued assembly group for the Komatsu 4D95S-W-1G-AS(S/N 23318-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Cooling System
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cooling System : Water Pump And Cooling Fan(#24252-)
01***16Screw5
01***25Bolt - Relay Mounting2
01***20Screw2
See all parts with full part numbers in Heavy Parts AI →
Cylinder Block
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Block : Camshaft And Tappet
01***20Screw2
04***16Fitting Wedge1
62***31Thrust Washer1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Block : Crankshaft
61***20Bolt1
62***00Crankshaft Ass'Y1
62***00Main Metal Ass'Y5
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Block : Cylinder Block
01***55Bolt, Mount Tube To Switch Pump8
01***16Screw1
01***20Screw2
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Block : Flywheel And Flywheel Housing
01***30Bolt6
01***30Bolt - Lower Oil Cooler Outlet Tubemounting11
01***45Bolt, Bracket Mounting8
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Block : Front Cover And Gear
01***10Bolt1
01***70Bolt,(For 75a Alternator)1
01***16Bolt2
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Block : Oil Pan (Cold Terrain Spec.)(#24252-)
01***14Bolt24
07***12Washer, Gasket,(Without Thermo Sensor) (K1)1
07***16Gasket,(For Pc750-6) (See Fig.A2110)1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Block : Oil Pan(#23318-74638)
01***16Bolt, Mount Solenoid Valve24
01***16Screw24
07***16Gasket,(For Pc750-6) (See Fig.A2110)1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Block : Oil Pan(#74639-)
01***20Bolt,(Forwarded Individually Parts)24
07***16Gasket,(For Pc750-6) (See Fig.A2110)1
62***12Pan,Oil1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Block : Piston And Connecting Rod
04***12Ring, Snap8
62***40Piston (S)4
62***00Piston Ring Ass'Y,Per Cylinder4
See all parts with full part numbers in Heavy Parts AI →
Cylinder Head
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Head : Air Cleaner And Mounting
01***30Bolt,(Water Separator Spec.)1
01***16Bolt,(With Alternator Cover Type)2
01***06Nut1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Head : Air Intake Manifold And Connection(#23318-30907)
01***65Stud1
01***65Bolt,(With Water Separator)3
01***75Bolt,(For Shipping)8
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Head : Air Intake Manifold And Connection(#30908-)
01***65Stud1
01***12Bolt,(With Speedometer)4
01***65Bolt,(With Water Separator)3
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Head : Cylinder Head
01***20Bolt, Hose Clamps (Inlet And Return Line Hoses)4
01***32Washer,(Not Used With Emergency Str.)17
02***04Plug, Pipe1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Head : Cylinder Head Cover
61***10Cap, Oil Filler1
61***20Screw3
61***30Washer,(B)3
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Head : Exhaust Manifold And Muffler
01***25Grub Screw4
01***45Bolt, Bracket Mounting8
01***11Nut (M14-1.50 Thd), Nut; Was 01582-014112
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Cylinder Head : Rocker Arm
01***12Bolt,(Without R.P.C.U.)1
01***65Bolt,(For Alternator Bracket Mount)5
61***30Nut8
See all parts with full part numbers in Heavy Parts AI →
Electrical System
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Electrical System : Alternator (15a)
60***60Alternator A. (15a)1
KD***70Cover1
KD***30Retainer2
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Electrical System : Alternator (25a)
60***10Alternator A. (25a)1
KD***57Bearing,Ball? Front1
KD***11Rear Bracket Ass'Y1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Electrical System : Alternator And Mounting (15a)
01***25Bolt,(With Corrosion Resistor)1
01***45Bolt1
01***06Nut1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Electrical System : Alternator And Mounting (25a)
01***55Bolt,(With Engine Stop Motor Type)1
01***30Bolt1
01***11Nut,(For Center Guard)1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Electrical System : Starting Motor (2.8kw)
60***70Starting Motor Ass'Y,(2.8kw)1
KD***60Bracket,Center1
KD***50Stopper,Piston1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Electrical System : Starting Motor And Mounting (2.8kw)
01***30Bolt2
07***95O-Ring,Transmission Strainer1
(6***0)Starting Motor Ass'Y,(2.8kw) (See Fig.A6210-B0b3)1
See all parts with full part numbers in Heavy Parts AI →
Engine Kit
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Engine Kit : Gasket Kit
01***12Washer,Lock (Noise Suppression Spec.) (K2)1
07***65O-Ring,Injection Pump Case1
07***85O-Ring,(Without Fuel Level Gauge)1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Engine Kit : Gasket Kit (Cold Terrain Spec.)(#24252-)
01***12Washer,Lock (Noise Suppression Spec.) (K2)1
07***18O-Ring,(See Fig.1601-29?1602-17)1
07***20O-Ring,Relief Valve1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Engine Kit : Gasket Kit(#24252-)
01***12Washer,Lock (Noise Suppression Spec.) (K2)1
07***18O-Ring,(See Fig.1601-29?1602-17)1
07***20O-Ring,Relief Valve1
See all parts with full part numbers in Heavy Parts AI →
Fuel System
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Fuel System : Fuel Filter And Piping
01***65Bolt,(With Water Separator)2
07***12Gasket,Mechanical Pump Piping1
07***12Gasket,(Without Air Compressor Type) (K1)4
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Fuel System : Fuel Injection Pump (Feed Pump)
DK***20Bolt, Joint1
DK***00Valve,Check2
DK***20Pump,Priming1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)
DK***00Shim? 2.00mm,(High Altitude Spec.)0
DK***00Adapter1
DK***80Nut1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)
DK***20Lever1
DK***40Gasket,Air Compressor2
DK***20Capsule,Spring1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Fuel System : Fuel Injection Pump (Pump) (1/2)
62***30Injection Pump Ass'Y1
62***31Injection Pump Ass'Y1
DK***30Bearing0
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Fuel System : Fuel Injection Pump (Pump) (2/2)
DK***40Shim? 0.50mm, Shim, 0.50mm; Was Dk029311-00400
DK***90Shim? 0.25mm, Shim, 0.25mm; Was Dk029311-05900
DK***00Sleeve,Control4
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Fuel System : Fuel Injection Pump And Piping
01***35Stud4
01***12Bolt2
01***25Screw2
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Fuel System : Fuel Nozzle And Spill Pipe
07***50Tube,Spill1
07***55Tube,Spill1
07***85Clip2
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Fuel System : Water Separator And Piping(#43240-)
01***80Stud2
01***25Bolt,(With Corrosion Resistor)2
01***08Nut,See Fig. K4010-04a02
See all parts with full part numbers in Heavy Parts AI →
Lubricating Oil System
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Lubricating Oil System : Lubricating Oil Cooler
01***25Bolt,(With Corrosion Resistor)4
01***30Bolt,(Water Separator Spec.)7
01***50Bolt,(With Corrosion Resistor)1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Lubricating Oil System : Lubricating Oil Filter
01***25Bolt,(With Corrosion Resistor)4
07***12Washer, Gasket,(Without Thermo Sensor) (K1)1
60***40Cartridge,Engine Oil Filter (D31s)1
See all parts with full part numbers in Heavy Parts AI →
Komatsu : 4d95s-W-1g-As(S/N 23318-Up) : Lubricating Oil System : Lubricating Oil Pump And Suction Pipe
01***12Bolt,(See Fig.0501)1
01***16Screw6
01***55Bolt,(With Engine Stop Motor Type)1
See all parts with full part numbers in Heavy Parts AI →

4D95S-W-1G-AS(S/N 23318-UP) serial number reference

Locate the engine data plate on the left side of the engine block, near the injection pump or valve cover. Read the model code (e.g., 4D95S-W-1G-AS) and the serial number. Match the serial number to the catalog range. The 3-character PIN (KMT) is for the machine chassis, not the engine; use the engine model code for parts identification.

PrefixIdentifies
4D95S-W-1G-ASEngine Model

Frequently asked questions

What engine powers the Komatsu 4D95S-W-1G-AS?

The Komatsu 4D95S-W-1G-AS is a 4-cylinder, water-cooled, turbocharged diesel engine from the 95 Series family, producing approximately 137 horsepower. It is used in GD85A and GD105A bulldozers.

What is the operating weight of the machine this engine powers?

The operating weight varies by configuration and undercarriage setup, typically ranging from 9,182 to 87,083 lb across the broader Komatsu catalog, with specific GD85A/GD105A weights depending on blade and counterweight options.

What replaced the 4D95S-W-1G-AS engine?

The 4D95S-W-1G-AS was succeeded by the 4D95S-1J and 4D95S-1J-T engines as Komatsu transitioned to later emissions tiers and updated the GD series bulldozers to newer dash generations.

What 4D95S-W-1G-AS(S/N 23318-UP) owners discuss

What are the typical powertrain and hydraulic behaviors associated with the Komatsu 4D95S-W-1G-AS engine series?
The 4D95S is the most powerful version in the basic 4D95 line, producing approximately 137 horsepower. It is designed for heavy work and powers machines such as the GD85A and GD105A bulldozers. The Komatsu line is generally noted for being smooth to run and very fuel efficient compared to early series competitors. However, the hydraulic pump and valve combinations have undergone significant updates and complete redesigns across different series. If the hydraulic pump fails, the engine is often at risk of failure shortly after, which is a common factor in the resale value of these machines. Dash 6 machines in this family are particularly known to have valve problems, especially on PC150 and PC120 models.
What undercarriage or wear patterns are typical for machines powered by this engine type?
The Komatsu line is generally designed to wear out complete machines simultaneously rather than individual components failing in isolation. This means undercarriage wear, hydraulic pump failure, and engine issues often occur in close proximity. Operators note that the line performs poorly on resale value, partly because major systems tend to fail together. For machines like the D21P-6, liners can show significant roughness and head gaskets may fail, indicating that wear patterns often involve multiple major engine components requiring simultaneous attention.
What are the known engine quirks for the 4D95S series regarding rebuilds and parts?
The 4D95S-W engines often face piston height mismatches during rebuilds. The engine uses pistons in two height variants: 95mm and 115mm. Installing shorter pistons, such as 95mm instead of the required 115mm, can cause compression loss and poor engine performance. Operators must verify piston height against engine specifications before installation. Additionally, the engine is sometimes confused with Yanmar motors, but it is a Komatsu unit. Parts availability can be difficult for gray market Komatsu machines unless the specific parts book and numbers are available.
What are common electrical or sensor issues reported for this engine family?
Common electrical issues include the fuel stop solenoid failing, which may require manual engine stopping via cable. Diagnostic fault codes frequently indicate engine controller power failure (E10), engine control failure with reduced output power to protect the engine (E11), and engine sensor malfunctions related to temperature or fuel (E15). The EPC system (E02) and parking brake system (E03) are also common sources of error codes. Defective EPS system transistors or excess current detection (E50) may also appear.
What should be checked when buying a used machine with the 4D95S-W-1G-AS engine?
Inspect the machine for oil, fuel, or coolant leaks, as these can lead to bigger problems. Verify the exact serial-prefix specification sheet and installed attachment package, as configurations like long sticks, wide track shoes, or regional emissions packages change weight and fuel use. Check the hydraulic pump and valve condition, as failure here often precedes engine failure. Ensure the fuel stop solenoid is functional. If the pump has been removed, have the pump timing rechecked, as incorrect timing causes low performance. For inline pumps, check the timing procedure; for rotary pumps, use a special tool and dial gauge to set timing accurately. Verify piston height if the engine has been rebuilt to ensure it matches the 95mm or 115mm specification.
What fluids are recommended for the Komatsu 4D95S engine family?
Use Komatsu recommended fluids, including Komatsu EO, TO, AXO, and HO for engine oil, hydraulic fluid, and coolant. Specific recommendations may vary by configuration and series. Komatsu Oil/Fuel & Wear Analysis (KOWA) is available for monitoring fluid condition. Chevron offers product recommendations for Komatsu equipment, including off-road segment manager specifications.
How is the fuel system typically diagnosed if the engine runs poorly after maintenance?
If the engine runs poorly after maintenance, such as after replacing rings or head gaskets, the issue is likely in the fuel delivery system rather than mechanical work. Crack injector lines to relieve pressure; if no fuel drips, there is air in the line. If fuel drips but there is no change in performance, the injector may be faulty. Cracking lines on cylinders 2 and 4 while the engine stops indicates cylinder 3 is also in trouble. Take injectors to a specialist diesel shop for re-calibration and new tips rather than using reconditioned tips. Blow out injector pipes with compressed air before fitting to remove dust that can jam the injector needle. Have an accredited specialist diesel fitter tune the fuel system.

Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.

Need a specific 4D95S-W-1G-AS(S/N 23318-UP) part?

Search live OEM part data, check fitment, and cross-reference alternatives with Heavy Parts AI.