Komatsu 3D78AE-3C(S/N 00101-UP)
Maintenance schedule, common problems & OEM parts breakdown
The Komatsu 3D78AE-3C engine (S/N 00101-UP) is a Tier 4 Final compliant diesel powerplant designed for compact and mini excavator applications, specifically the PC27R-8, PC30MR-3, PC35MR-3, and PC45MR-3 series. This engine family operates within the 9,182 to 12,688 lb operating weight class for host machines. Production for this specific serial range covers the transition into the PC27R-8 and PC30MR-3 generations, succeeding earlier PC27MR-3 and PC30MR-5 models. Configurations offered include standard and deluxe boom/stick options, with the engine integrated into the undercarriage and chassis systems of these compact excavators.
Across the 3D78AE series generations, the primary change from the -3A and -3B variants to the -3C (S/N 00101-UP) is the implementation of Tier 4 Final emissions standards, requiring advanced aftertreatment systems like KDPF and SCR. This shift necessitates the use of specific Komatsu Genuine Lubricants and DEF, altering the maintenance ecosystem compared to earlier Tier 3 models. The machine remains significant in the used and parts market because the 3D78AE-3C is a common powerplant for high-volume mini excavators still widely deployed in municipal and utility work, driving demand for specific engine overhaul kits, fuel injection components, and undercarriage parts.
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-3C(S/N 00101-UP) specifications
Engine
| Model | 3D78AE-3C |
| Series | 78 Series |
| Cylinders | 3 |
| Displacement | 1.2 L (73.5 cu. in.) |
| Emissions Tier | Tier 4 Final |
Weights
| Operating Weight | Not documented for this exact serial range — verify with your dealer |
| 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 |
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-3C(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-3C(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 (iron, copper, lead) and contaminants. Check coolant SCA concentration at 500 hours to prevent scaling and corrosion in the 3D78AE-3C cooling passages. Monitor hydraulic oil particle count and viscosity to protect the high-pressure pump. Track DEF levels daily to ensure SCR system functionality. Use Komatsu Genuine Lubricants to maintain additive packages specified for Tier 4 Final engines. Analyze fuel dilution and soot levels in engine oil to detect combustion inefficiencies early.
Corrective & Common Repairs
Address fuel system issues by replacing the fuel filter and draining the water separator regularly to protect the 3D78AE-3C injection pump. Inspect the turbocharger at 1,000 hours for shaft play and housing damage. Check hydraulic hoses for cracks and leaks during daily walks. Replace worn belts and clamps at 2,000 hours to prevent accessory failure. Inspect the KDPF for clogging and perform regeneration or cleaning as needed. Verify battery terminal integrity and alternator output to ensure reliable starting in compact excavator applications.
Overhaul & Rebuild Points
Plan major engine overhaul based on KOWA results and compression testing for the 3D78AE-3C cylinder block. Inspect piston rings and cylinder liners for wear during major service intervals. Check crankshaft bearings and camshaft bushings for clearance limits. Replace head gaskets and valve seals if compression drops or oil consumption increases. Inspect the fuel injection pump and nozzles for spray pattern and leakage. Evaluate the turbocharger for bearing wear and seal integrity before failure.
Seasonal & Environment Servicing
In cold climates, check coolant freeze protection and use appropriate viscosity engine oil for the 3D78AE-3C. Ensure DEF is stored and used within temperature specifications to prevent crystallization. In dusty environments, inspect the air filter more frequently and clean the radiator and oil cooler fins daily to prevent overheating. Check track tension and undercarriage components for mud buildup and wear. Inspect hydraulic system seals for moisture ingress in wet conditions. Verify battery charge and electrolyte levels in extreme temperatures.
3D78AE-3C(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 → |
| YM119810-35300 | Intake Oil Filter | Lubrication service | Check fitment → |
| YM121120-12901 | Element | Scheduled service item | Check fitment → |
| YM129150-35152 | Filter Element | Scheduled service item | Check fitment → |
Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.
3D78AE-3C(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 the voltage at the pin connector |
| CA111 | Internal engine controller fault | ECM internal abnormality | 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 |
| CA234 | Engine overspeed | Throttle calibration error, engine load cycle issue, or operator misuse | Verify throttle calibration and engine load cycle |
| CA441 | Battery voltage too low | Alternator failure, battery degradation, or voltage regulator issue | Replace the alternator or battery; check the voltage regulator |
| AA10NX | Air cleaner clogging | Dirty or blocked air filter element | Replace the air filter |
| CA122 | Intake air pressure high voltage | Intake pressure 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) | Faulty IAT sensor | Replace or test the IAT sensor |
| CA154 | Intake air temperature sensor error (low) | Faulty IAT sensor | Replace or test the IAT sensor |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
3D78AE-3C(S/N 00101-UP) attachments & work tools
Mini Excavator Buckets
Standard and heavy-duty digging buckets for the 2.5–2.8 ton class (e.g., PC26MR-3, PC30MR-3) are typical for this engine size. Capacities generally range from 0.035 to 0.085 m³ depending on the specific machine model and application. These tools are mounted via the standard quick coupler system found on compact excavators.
Skid Steer Attachments
Compatible with the SK05J-2, SK07J-2, SK815-5, and SK818-5 skid steer loader platforms. Typical work tools include general purpose buckets, grading buckets, and pallet forks. Mounting utilizes the standard skid steer quick-attach interface.
Wheel Loader Buckets
Designed for the WA50-6 wheel loader application. Bucket capacities vary by configuration but are sized for the 5,000 kg class loader. Standard rock, light material, and multi-purpose buckets are available with the appropriate mounting pins and hydraulic lines for lift and tilt functions.
Hydraulic Piping and Kits
Work tools requiring auxiliary hydraulics (e.g., breakers, augers, tilt rotators) require specific piping kits. The engine's hydraulic pump output (YM129001-32002/YM129407-32001 variants) must be matched to the tool's flow requirements. Kits typically include high-pressure hoses, quick-connect couplers, and mounting brackets.
Factory Guarding and Options
Factory configurations may include FOPS/ROPS certified canopies for operator protection. Additional options often involve extended cooling packages for high-ambient temperature operation and specific exhaust configurations to meet Tier 4 Final or local emission standards.
All 3D78AE-3C(S/N 00101-UP) assemblies by section
Every catalogued assembly group for the Komatsu 3D78AE-3C(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-3c(S/N 00101-Up) : Accessory : P.P.C. Pump And Mounting(#00112-)
| YM***64 | Bearing,Ball | 2 |
| YM***50 | Bracket | 1 |
| YM***02 | Stud | 4 |
Cooling System
Komatsu : 3d78ae-3c(S/N 00101-Up) : Cooling System : Water Pump And Cooling Fan(#00112-)
| YM***02 | Bolt Plated | 2 |
| YM***20 | O-Ring,(Not Shown) | 1 |
| YM***11 | Gasket (Kit) | 1 |
Cylinder Block
Komatsu : 3d78ae-3c(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-3c(S/N 00101-Up) : Cylinder Block : Crankshaft
| YM***00 | Gear,Crank | 1 |
| YM***80 | Parallel Pin | 1 |
| YM***50 | Pulley,Crank | 1 |
Komatsu : 3d78ae-3c(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-3c(S/N 00101-Up) : Cylinder Block : Flywheel And Flywheel Housing(#00112-)
| YM***50 | Oil Seal Case, Assembly | 1 |
| YM***00 | Gear,Ring | 1 |
| YM***80 | Seal? Rear | 1 |
Komatsu : 3d78ae-3c(S/N 00101-Up) : Cylinder Block : Front Cover And Gear(#00112-)
| YM***51 | Cap, Lub. Oil Supply | 1 |
| YM***52 | Bolt | 4 |
| YM***40 | O-Ring,Drain Plug | 1 |
Komatsu : 3d78ae-3c(S/N 00101-Up) : Cylinder Block : Oil Pan(#00112-)
| YM***52 | Screw | 22 |
| YM***40 | Plug,Drain | 1 |
| YM***90 | Oil Pan Ass'Y | 1 |
Komatsu : 3d78ae-3c(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-3c(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-3c(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-3c(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-3c(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-3c(S/N 00101-Up) : Cylinder Head : Exhaust Manifold And Muffler(#00112-)
| YM***02 | Stud | 1 |
| YM***80 | Collar | 2 |
| YM***22 | Stud | 4 |
Komatsu : 3d78ae-3c(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-3c(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-3c(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-3c(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-3c(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-3c(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-3c(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-3c(S/N 00101-Up) : Fuel System : Fuel Filter And Piping
| YM***70 | Union | 1 |
| YM***40 | Lever | 1 |
| YM***00 | Hose | 2 |
Komatsu : 3d78ae-3c(S/N 00101-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)(#00112-)
| YM***02 | Lever Ass'Y,Stop | 1 |
| YM***10 | Pin,Stop Lever | 1 |
| YM***00 | O-Ring (Kit) | 1 |
Komatsu : 3d78ae-3c(S/N 00101-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)(#00112-)
| YM***01 | Weight Assembly., Governor | 1 |
| YM***90 | Shaft,Governor Lever | 1 |
| YM***16 | Pin,Spring | 1 |
Komatsu : 3d78ae-3c(S/N 00101-Up) : Fuel System : Fuel Injection Pump (Pump) (1/2)(#00112-)
| YM***50 | Kit, Shim | 1 |
| YM***10 | Plate? Caution | 1 |
| YM***50 | Cover,Side | 1 |
Komatsu : 3d78ae-3c(S/N 00101-Up) : Fuel System : Fuel Injection Pump (Pump) (2/2)(#00112-)
| YM***70 | Retainer, Spring | 3 |
| YM***00 | Plunger W/Barrel | 3 |
| YM***02 | Screw | 2 |
Komatsu : 3d78ae-3c(S/N 00101-Up) : Fuel System : Fuel Injection Pump And Piping(#00112-)
| YM***20 | Retainer, Pipe | 1 |
| YM***60 | O-Ring,Fuel Injection Pump | 1 |
| YM***20 | Pipe,Injection? No.2 | 1 |
Komatsu : 3d78ae-3c(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-3c(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-3c(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-3c(S/N 00101-Up) : Tool And Kit : Gasket Kit(#00112-)
| YM***60 | O-Ring,Fuel Injection Pump | 1 |
| YM***40 | O-Ring,Drain Plug | 1 |
| YM***10 | Gasket,Exhaust Manifold | 1 |
Komatsu : 3d78ae-3c(S/N 00101-Up) : Tool And Kit : Tool(#00112-)
| YM***70 | Wrench | 1 |
| YM***20 | Wrench | 1 |
| YM***50 | Screw Driver | 1 |
Frequently asked questions
What engine does the Komatsu 3D78AE-3C (S/N 00101-UP) use?
The Komatsu 3D78AE-3C (S/N 00101-UP) is a Tier 4 Final compliant diesel engine used in compact excavators like the PC27R-8 and PC30MR-3.
What is the operating weight of the machine powered by this engine?
The operating weight varies by configuration and series, typically ranging from 9,182 to 12,688 lb for the host compact excavator models.
What replaced the Komatsu 3D78AE-3C engine?
The 3D78AE-3C is part of the 3D78AE series, which succeeded earlier 3D78AE-3A and 3D78AE-3B variants. It is used in the PC27R-8 and PC30MR-3 series, which succeeded the PC27MR-3 and PC30MR-5 models.
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