Komatsuengine(no series)
Komatsu S6D125-1JJ-FA(S/N 10001-UP)
Maintenance schedule, common problems & OEM parts breakdown
The Komatsu S6D125-1JJ-FA is a turbocharged and aftercooled diesel engine belonging to the S6D125 series, designed for heavy construction applications. It powers the D65EX-12 and D65PX-12 generation crawler dozers, which are mid-size machines in the 12-series family. These dozers typically operate in the 20,000 to 60,000 lb weight range, depending on configuration (standard gauge E/EX vs. wide-gauge LGP P/PX). The S6D125-1JJ-FA succeeded earlier naturally aspirated 6D125-1 variants and was later superseded by electronically controlled turbocharged engines introduced with the D65EX-15/D65PX-15 generation in the early-to-mid 2000s. Configurations offered include standard straight-tilt blade and wide-gauge low-ground-pressure swamp setups.
Across the 12-series generation, the primary change was the shift from naturally aspirated to turbocharged and aftercooled architectures to increase power density and meet evolving performance demands. The S6D125-1JJ-FA matters in the used and parts market because it represents the high-output turbo variant used on the popular EX/PX chassis, distinct from the base naturally aspirated 6D125-1A. Its robust block design and shared bore/stroke with the SA6D125E-2 family ensure a wide availability of aftermarket and genuine parts. The machine remains a staple in earthmoving fleets due to its durability, making it a critical reference point for fleet managers managing legacy Komatsu dozer inventory.
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 S6D125-1JJ-FA(S/N 10001-UP) specifications
Engine
| Model | S6D125-1JJ-FA |
| Series/Generation | 125 Series |
| Configuration | Turbocharged and aftercooled |
| Aspiration | Turbocharged and aftercooled |
| Displacement | Not documented for this exact serial range — verify with your dealer |
| Cylinders | Not documented for this exact serial range — verify with your dealer |
| Emissions Tier | Not documented for this exact serial range — verify with your dealer |
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 S6D125-1JJ-FA(S/N 10001-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 S6D125-1JJ-FA(S/N 10001-UP) beyond the schedule
Predictive Maintenance & Fluid Analysis
Utilize Komatsu KOWA fluid analysis at every 500-hour interval to monitor engine wear metals (iron, copper, lead, aluminum) and contaminants (silicon for dirt, sodium for coolant). Track hydraulic fluid particle count and viscosity to detect pump or valve wear early. Monitor coolant pH, SCA concentration, and glycol content to prevent corrosion and cavitation in the S6D125-1JJ-FA block. KOMTRAX telematics integration allows remote tracking of load frequency and fault codes, enabling proactive scheduling before component failure occurs.
Corrective & Common Repairs
Address common S6D125-1JJ-FA issues by inspecting the turbocharger TV7705 for shaft play and bearing wear, a frequent failure point under heavy load. Check the fuel injection pump TVC setting, which varies by application; improper adjustment can cause excessive valve train damage. Inspect the water pump and thermostat housing for coolant leaks that lead to crankcase contamination. Replace worn V-belts and tensioners to prevent alternator and fan drive failure, ensuring proper cooling and electrical system function.
Overhaul & Rebuild Points
Plan inframe overhaul for the S6D125-1JJ-FA around 10,000 to 15,000 hours, focusing on piston rings, cylinder liners, and bearings. Use the S6D125-1 engine inframe overhaul kit for piston components. Inspect the crankshaft for journal wear and the cylinder head for valve seat integrity. Replace the turbocharger if exhaust output drops or oil consumption increases significantly. Structural inspections of the boom and stick welds are critical during major service intervals to ensure chassis integrity matches engine health.
Seasonal & Environment Servicing
In cold climates, ensure the coolant system uses Komatsu Super Coolant AF-NAC to prevent freezing and maintain proper SCA levels. Drain the fuel water separator daily to prevent ice formation in the lines. In dusty environments, monitor the air filter restriction indicator closely and clean the outer element more frequently than the standard 1,000-hour interval. Inspect the radiator and oil cooler fins for debris buildup to maintain heat rejection efficiency, especially during high-load earthmoving operations in summer conditions.
S6D125-1JJ-FA(S/N 10001-UP) common service parts
| Part number | Part | Notes | |
|---|---|---|---|
| 600-311-8291 | Cartridge,Fuel Filter | Fuel system service | Check fitment → |
| 600-311-9100 | Fuel Filter Ass'Y | Fuel system service | Check fitment → |
| 07281-00197 | Clamp,(With Pre-Fuel Filter) | Fuel system service | Check fitment → |
| 09637-02161 | Plate? Instruction,Air Cleaner (Double Element) | Air intake service | Check fitment → |
| 09637-30161 | Plate? Instruction,Air Cleaner (Single Element) | Air intake service | Check fitment → |
Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.
S6D125-1JJ-FA(S/N 10001-UP) fault codes & troubleshooting
| Code | Meaning | Likely cause | What to do |
|---|---|---|---|
| CA115 | Engine crankshaft speed sensor and backup speed sensor failure | Faulty speed sensor, broken wiring harness, or corroded connector at the pin connector | Replace the speed sensor and verify voltage at the pin connector |
| CA111 | Internal engine controller fault | Malfunction within the Electronic Control Module (ECM) | Replace or reprogram the ECM |
| CA451 | Common rail pressure sensor feedback value too high | Malfunction in the rail pressure sensor or actual overpressure condition | Diagnose the fuel rail pressure sensor or check pump lines |
| CA122 | Intake air pressure sensor feedback voltage too high | Faulty intake pressure sensor or wiring issue | Verify the intake pressure sensor and wiring |
| CA123 | Intake air pressure sensor feedback voltage too low | Sensor short or airflow restriction | Check for a sensor short or an airflow restriction |
| CA441 | Battery voltage too low | Weak battery or failing alternator | Replace the alternator or battery; check the voltage regulator |
| CA442 | Battery voltage too high | Failing voltage regulator or alternator overcharging | Replace the alternator or battery; check the voltage regulator |
| CA234 | Engine overspeed | Throttle calibration error, engine load cycle issue, or operator misuse | Verify throttle calibration, engine load cycle, or operator misuse |
| CA153 | Intake air temperature sensor feedback voltage too high | Faulty Intake Air Temperature (IAT) sensor | Replace or test the IAT sensor |
| CA154 | Intake air temperature sensor feedback voltage too low | Faulty Intake Air Temperature (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.
S6D125-1JJ-FA(S/N 10001-UP) attachments & work tools
Excavator Attachments
The S6D125-1JJ-FA engine powers the PC400-6 and PC400LC-6 excavator series. Standard bucket capacities for this class typically range from 1.5 to 2.5 cubic meters (1.96 to 3.27 cubic yards), varying by configuration and series. These machines utilize standard quick coupler systems and require auxiliary hydraulic kits for breakers or hammers.
Wheel Loader Attachments
This engine is installed in the WA470-3 and WA470-5 wheel loaders. Typical bucket capacities for these models range from 2.5 to 3.5 cubic meters (3.27 to 4.58 cubic yards). Factory configurations include standard lift arms and optional high-lift arms, with hydraulic flow rates supporting standard grapple or multi-purpose bucket options.
Bulldozer Attachments
The S6D125-1JJ-FA is used in the D65E-12 and D65PX-12 dozer series. Blade capacities vary by configuration, with straight tilt blades (E/EX) and semi-U blades (P/PX) offering capacities between 8 and 10 cubic meters (10.46 to 13.08 cubic yards). Guarding options include side cutters and edge guards, with ripper configurations available for the rear mount.
Hydraulic and Mounting Systems
Work tool compatibility relies on standard Komatsu quick-attach interfaces and auxiliary hydraulic circuits. Hydraulic kit requirements vary by configuration and series depending on the specific tool flow demands. Engine mounting points are standardized for the PC400, WA470, and D65E chassis families.
All S6D125-1JJ-FA(S/N 10001-UP) assemblies by section
Every catalogued assembly group for the Komatsu S6D125-1JJ-FA(S/N 10001-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Engine
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Additionl Fuel Filter(#11574-)
| 07***12 | Gasket,Mechanical Pump Piping | 2 |
| 60***91 | Cartridge,Fuel Filter | 1 |
| 60***00 | Fuel Filter Ass'Y | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Air Cleaner And Mounting(#11574-)
| 01***40 | Bolt,(Dust And Dirt Protection) | 2 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 4 |
| 01***50 | Bolt,(With Service Valve R.H.) | 2 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Air Compressor (Inner Parts)(#11574-41217)
| 61***10 | Air Compressor Ass'Y,(See Fig.0711) | 1 |
| DK***20 | Connecting Rod A | 1 |
| DK***00 | Spring,Delivery Valve | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Air Compressor (Inner Parts)(#26688-40873)
| 61***10 | Air Compressor Ass'Y,(See Fig.0711) | 1 |
| DK***20 | Connecting Rod A | 1 |
| DK***00 | Spring,Delivery Valve | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Air Compressor (Inner Parts)(#40874-)
| 61***11 | Air Compressor Ass'Y,(See Fig.0711a) | 1 |
| 61***12 | Air Compressor Ass'Y,(See Fig.0711a) | 1 |
| DK***20 | Connecting Rod A | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Air Compressor (Inner Parts)(#41218-)
| 61***11 | Air Compressor Ass'Y,(See Fig.0711a) | 1 |
| 61***12 | Air Compressor Ass'Y,(See Fig.0711a) | 1 |
| DK***20 | Connecting Rod A | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Air Compressor And Piping(#11574-)
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***40 | Bolt, Mount Master Brake Cylinder | 1 |
| 01***16 | Washer,Radio Controlled Slag Handling | 2 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Air Intake Manifold And Connection(#11574-)
| 01***10 | Bolt,(With Auto Emergency Steering) | 2 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 13 |
| 01***40 | Bolt, Mount Master Brake Cylinder | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Alternator (25a) (Inner Parts)(#11574-)
| 60***40 | Alternator A. (25a),(With Hardening Pulley) | 1 |
| 60***20 | Alternator A. (25a),(With Hardening Pulley) | 1 |
| KD***57 | Bearing,Ball? Front | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Alternator (35a) (Inner Parts)(#11574-16546)
| 60***20 | Alternator A. (35a),(With Hardening Pulley) | 1 |
| KD***57 | Bearing,Ball? Front | 1 |
| KD***80 | Collar | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Alternator (35a) (Inner Parts)(#16547-)
| 60***20 | Alternator A. (35a),(With Hardening Pulley) | 1 |
| KD***80 | Collar | 1 |
| KD***70 | Rear Bracket Ass'Y,Rear | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Alternator (50a) (Inner Parts)(#11574-16546)
| 60***30 | Alternator A. (50a),(With Non Hardening Pulley) | 1 |
| 60***60 | Alternator A. (50a),(With Hardening Pulley) | 1 |
| SD***X0 | Pulley,Non Hardening | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Alternator (50a) (Inner Parts)(#16547-)
| 60***70 | Alternator A. (50a),(With Hardening Pulley) | 1 |
| 60***80 | Alternator A. (50a),(With Non Hardening Pulley) | 1 |
| SD***X0 | Washer | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Alternator And Mounting(#11574-)
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***30 | Bolt | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Camshaft
| 01***22 | Bolt | 2 |
| 04***25 | Key, Plain Woodruff | 1 |
| 04***12 | Ring,Snap (For Ripper) | 2 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Cooling Fan And Mounting(#11574-)
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 22 |
| 01***40 | Bolt, Mount Master Brake Cylinder | 2 |
| 01***15 | Bolt,(With Air Conditioner Type) | 4 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Corrosion Resistor And Piping(#11574-)
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 4 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Crankshaft(#11574-)
| 01***25 | Bolt,(Without Rops Guard? Canopy) | 6 |
| 01***30 | Screw | 1 |
| 01***35 | Screw | 5 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Cylinder Block (Cold Terrain Spec.)(#11574-)
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
| 01***12 | Bolt,(Without Air Compressor Type) | 2 |
| 01***16 | Washer,Radio Controlled Slag Handling | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Cylinder Block Cover
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 2 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 2 |
| 01***16 | Washer,Radio Controlled Slag Handling | 2 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Cylinder Block(#11574-)
| 01***12 | Bolt,(Without Air Compressor Type) | 2 |
| 01***45 | Washer,(For Travel Motor) (Not Show) | 14 |
| 04***14 | Pin, Dowel | 2 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Cylinder Head(#10001-26690)
| 04***20 | Pin,Dowel (Welded) | 2 |
| 61***30 | Sleeve,Holder | 1 |
| 61***20 | Cotter, Valve | 48 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Cylinder Head(#26691-)
| 04***20 | Pin,Dowel (Welded) | 2 |
| 61***30 | Sleeve,Holder | 1 |
| 61***20 | Cotter, Valve | 48 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Engine Stop Motor And Mounting (Key Stop Type)(#23904-)
| 01***25 | Bolt,(For Automatic) | 3 |
| 01***20 | Bolt,(With Auto Emergency Steering) | 2 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Exhaust Manifold And Turbocharger(#11574-)
| 01***00 | Bolt (M10-1.50x100) | 18 |
| 01***45 | Screw | 4 |
| 07***08 | Plug,(Without Auto Priming System) | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Flywheel And Flywheel Housing(#11574-)
| 01***50 | Bolt, Radiator To Frame | 6 |
| 01***60 | Bolt, Hanger Bearing Mounting | 2 |
| 01***45 | Bolt,(For Power Tilt Mech Angle) | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Front Cover(#11574-)
| 01***25 | Bolt,(Without Auto Priming System) | 6 |
| 01***30 | Bolt,(For France Noise Suppression) | 6 |
| 01***60 | Screw | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Fuel Filter And Piping(#11574-)
| 01***75 | Bolt,(For Adjusting) | 2 |
| 01***16 | Washer,Radio Controlled Slag Handling | 2 |
| 07***12 | Gasket,Mechanical Pump Piping | 2 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Fuel Injection Pump (Coupling) (Inner Parts)(#11574-)
| DK***00 | Coupling,Cross | 1 |
| DK***60 | Coupling Ass'Y | 1 |
| DK***00 | Nut | 2 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Fuel Injection Pump (Feed Pump) (Inner Parts)(#11574-)
| DK***20 | Bolt, Joint | 1 |
| DK***00 | Valve,Check | 2 |
| DK***80 | Feed Pump Ass'Y | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Fuel Injection Pump (Governor) (1/2) (Inner Parts)(#11574-)
| DK***00 | Screw | 1 |
| DK***20 | Flyweight Ass'Y | 1 |
| DK***00 | Shim? 2.00mm,(High Altitude Spec.) | 0 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Fuel Injection Pump (Governor) (2/2) (Inner Parts)(#11574-)
| DK***00 | Spring | 1 |
| DK***20 | Capsule,Spring | 1 |
| DK***00 | Nut,Cap | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Fuel Injection Pump (Pump) (Inner Parts)(#11574-)
| 61***10 | Injection Pump A.,(See Fig.0451) | 1 |
| 61***12 | Injection Pump A.,(See Fig.0451) | 1 |
| 61***13 | Injection Pump A.,(See Fig.0451) | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Fuel Injection Pump And Piping(#11574-)
| 01***30 | Bolt | 4 |
| 01***45 | Bolt,(For Power Tilt Mech Angle) | 2 |
| 01***55 | Bolt, Mount Tube To Switch Pump | 4 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Fuel Nozzle And Spill Pipe(#11574-)
| 01***45 | Bolt, Divider Valve Mounting | 12 |
| 07***65 | O-Ring,Cylinder Block | 6 |
| 07***12 | Gasket,Mechanical Pump Piping | 2 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Gasket Kit(#11574-)
| 02***43 | O-Ring,Water Manifold | 10 |
| 07***20 | O-Ring,Relief Valve | 1 |
| 07***15 | O-Ring,(For Low Speed) (D40pf) | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Head Cover
| 01***16 | Washer,Radio Controlled Slag Handling | 24 |
| 61***10 | Cover,Head? No.2?3?4?5?6 | 6 |
| 61***11 | Cover,Head? No.2?3?4?5?6 | 6 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Lubricating Oil Cooler(#11574-)
| 01***25 | Bolt,Without Revolution Sensor | 2 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 12 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Lubricating Oil Filter And Mounting
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 8 |
| 02***16 | Plug | 1 |
| 04***12 | Ring, Snap | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Lubricating Oil Piping(#11574-13430)
| 01***50 | Bolt,(With Service Valve R.H.) | 2 |
| 01***55 | Bolt, Mount Tube To Switch Pump | 2 |
| 01***16 | Washer,Radio Controlled Slag Handling | 7 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Lubricating Oil Piping(#13431-)
| 01***50 | Bolt,(With Service Valve R.H.) | 4 |
| 01***16 | Washer,Radio Controlled Slag Handling | 7 |
| 04***12 | Ring, Snap | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Lubricating Oil Pump And Suction Pipe(#11574-)
| 01***25 | Bolt,(Without Auto Priming System) | 4 |
| 01***20 | Bolt,(Large Capacity Type) (Std) | 2 |
| 01***25 | Bolt,(Sandy? Dusty Terrain Spec.) | 5 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Muffler (Tunnel Spec.)(#11574-)
| 01***40 | Bolt,(Dust And Dirt Protection) | 4 |
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 4 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Muffler(#11574-)
| 01***40 | Bolt,(Dust And Dirt Protection) | 4 |
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 4 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Oil Pan (Cold Terrain Spec.)(#11574-)
| 01***12 | Bolt, Bolt,(No Need To Quick Shift) | 3 |
| 01***12 | Bolt,(With Cylinder Cover) | 1 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Oil Pan (Extreme Cold Terrain Spec.)(#11574-)
| 01***16 | Bolt (With Air Heater & Conditioner) | 1 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 25 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Oil Pan(#11574-)
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 25 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 11 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Piston And Connecting Rod(#11574-)
| 02***13 | Pin, Dowel | 2 |
| 04***18 | Ring, Snap | 12 |
| 61***31 | Piston Ring Ass'Y | 6 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Rocker Arm
| 01***08 | Nut,R.H. Thread | 12 |
| 01***16 | Washer,Radio Controlled Slag Handling | 40 |
| 01***32 | Washer,(With Auto Emergency Steering) | 40 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Solenoid And Mounting (Key Stop Type)(#11574-15804)
| 01***16 | Bolt,(For Slag Handling) | 2 |
| 01***20 | Bolt,(Without Maintenance Monitor) | 4 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 3 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Solenoid And Mounting (Key Stop Type)(#15805-23903)
| 01***20 | Bolt,(Without Maintenance Monitor) | 4 |
| 01***65 | Bolt,(Except Japan) | 2 |
| 01***90 | Bolt, Fan Mounting | 2 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Solenoid Relay(#11574-28162)
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Starting Motor (11kw) (Inner Parts)(#11574-20299)
| 60***30 | Starting Motor Ass'Y,(11kw)(See Fig.0662) | 1 |
| SD***09 | Metal | 1 |
| SD***60 | O-Ring | 2 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Starting Motor (11kw) (Inner Parts)(#20300-35326)
| 60***20 | Starting Motor Ass'Y,(11kw)(See Fig.0662a) | 1 |
| 60***21 | Starting Motor Ass'Y,(11kw)(See Fig.0662a) | 1 |
| SD***X0 | Bar Ass'Y | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Starting Motor (11kw) (Inner Parts)(#35327-)
| 60***22 | Starting Motor Ass'Y,(11kw) | 1 |
| SD***X9 | Switch Ass'Y,Engage | 1 |
| SD***X0 | Bearing,Ball | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Starting Motor (7.5kw) (Inner Parts)(#11574-17373)
| 60***80 | Starting Motor Ass'Y,(7.5kw) | 1 |
| KD***20 | Magnetic Switch Assembly | 1 |
| KD***40 | Spring,Spring | 4 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Starting Motor (7.5kw) (Inner Parts)(#17374-)
| 60***80 | Starting Motor Ass'Y,(7.5kw) | 1 |
| KD***60 | Shift Lever Assembly | 1 |
| KD***40 | Spring,Spring | 4 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Starting Motor Mounting(#11574-)
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
| 01***40 | Bolt,(With Center Guard) | 3 |
| 08***19 | Band,(Without Air Conditioner) | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Turbocharger (Inner Parts)(#11574-23903)
| 61***00 | Turbocharger Ass'Y,(See Fig.0155) | 1 |
| 61***00 | Turbocharger Ass'Y,(Tv7705) | 1 |
| GA***85 | V-Band Ass'Y | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Turbocharger (Inner Patrs)(#23904-)
| 61***10 | Turbocharger Ass'Y,(Ta4532) | 1 |
| GA***60 | V-Band | 1 |
| GA***52 | Center Housing A | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Turbocharger Libricating Oil Piping(#26750-)
| 01***20 | Bolt,(With Auto Emergency Steering) | 2 |
| 01***30 | Bolt,(For Mechanical Governor) | 2 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 2 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Water Manifold(#11574-14646)
| 02***43 | O-Ring,Water Manifold | 10 |
| 07***12 | Washer, Gasket,(Without Thermo Sensor) (K1) | 1 |
| 07***15 | Plug,(Used When Without Heater) | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Water Manifold(#14647-)
| 02***43 | O-Ring,Water Manifold | 6 |
| 07***12 | Washer, Gasket,(Without Thermo Sensor) (K1) | 1 |
| 07***15 | Plug,(Used When Without Heater) | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Water Pump And Mounting(#11574-)
| 01***30 | Bolt,(For France Noise Suppression) | 2 |
| 01***16 | Bolt (With Air Heater & Conditioner) | 6 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 6 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Water Separator And Mounting (With Additional Fuel Filter)(#11574-)
| 01***30 | Bolt,(For France Noise Suppression) | 4 |
| 01***35 | Bolt, Mounting - Flywheel Housing End | 6 |
| 07***12 | Gasket,Mechanical Pump Piping | 1 |
Komatsu : S6d125-1jj-Fa(S/N 10001-Up) : Engine : Water Separator And Mounting (Without Additional Fuel Filter)(#11574-)
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
| 01***55 | Bolt | 1 |
S6D125-1JJ-FA(S/N 10001-UP) serial number reference
The S6D125-1JJ-FA PIN plate is located on the engine block, typically on the left side near the injection pump or on a metal data plate affixed near the valve cover. Read the prefix by identifying the first three characters of the engine model code stamped on the plate, which indicates the engine family and generation (e.g., 'S6D' for a 6-cylinder turbocharged diesel).
| Prefix | Identifies | Notes |
|---|---|---|
| S6D125-1JJ | Engine Model | S6D125-1JJ (S/N 11574-UP). Predecessor variant to the -1JJ-FA. Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1 | Engine Series | S6D125-1 (S/N 10001-UP). General series designation. Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| 6D125-1 | Engine Series | 6D125-1 (S/N 10001-UP). Non-turbo/standard designation variant. Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1C | Engine Model | S6D125-1C (S/N 10001-UP). Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1D | Engine Model | S6D125-1D (S/N 10001-UP). Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1E | Engine Model | S6D125-1E (S/N 10001-UP). Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1F | Engine Model | S6D125-1F (S/N 10001-UP). Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1M | Engine Model | S6D125-1M (S/N 10001-UP). Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1KK | Engine Model | S6D125-1KK (S/N 26750-UP). Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1AM | Engine Model | S6D125-1AM (S/N 51975-UP). Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1B8 | Engine Model | S6D125-1B8 (S/N 22230-UP). Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1CC | Engine Model | S6D125-1CC (S/N 10001-UP). Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1D-AR | Engine Model | S6D125-1D-AR (S/N 10001-UP). Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1D-FE | Engine Model | S6D125-1D-FE (S/N 10001-UP). Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1EE | Engine Model | S6D125-1EE (S/N 10001-UP). Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1M-FA | Engine Model | S6D125-1M-FA (S/N 10001-UP). Listed in Fab Heavy Parts engine application data. Confirm with dealer for exact serial break boundaries. |
| S6D125-1FF | Engine Model | S6D125-1FF (S/N 24781-UP). Listed in DK Engine Parts equipment guide. Confirm with dealer for exact serial break boundaries. |
| S6D125E-2A | Engine Model | S6D125E-2A (S/N 60863-UP). Listed in DK Engine Parts equipment guide. Confirm with dealer for exact serial break boundaries. |
| SA6D125E-3A | Engine Model | SA6D125E-3A (S/N 310314-UP). Listed in DK Engine Parts equipment guide. Confirm with dealer for exact serial break boundaries. |
| 6D125-1JJ | Engine Model | 6D125-1JJ (S/N 21829-Up). Listed in DK Engine Parts equipment guide. Confirm with dealer for exact serial break boundaries. |
| 6D125-1AF | Engine Model | 6D125-1AF (S/N 24586-Up). Listed in DK Engine Parts equipment guide. Confirm with dealer for exact serial break boundaries. |
| 6D125-1AN | Engine Model | 6D125-1AN (S/N 47990-Up). Listed in DK Engine Parts equipment guide. Confirm with dealer for exact serial break boundaries. |
Frequently asked questions
What type of engine is the S6D125-1JJ-FA?
It is a turbocharged and aftercooled diesel engine from the Komatsu S6D125 series, used in the D65EX-12 and D65PX-12 dozers.
What is the operating weight of the machines using this engine?
The operating weight varies by configuration/series, typically ranging from 20,000 to 60,000 lb for the D65EX-12/D65PX-12 dozer family.
What replaced the S6D125-1JJ-FA engine?
It was superseded by turbocharged, electronically controlled engines introduced with the D65EX-15/D65PX-15 generation dozers in the early-to-mid 2000s.
What S6D125-1JJ-FA(S/N 10001-UP) owners discuss
How does the S6D125-1JJ-FA engine's hydraulic pump setup differ from the L10 Cummins units found in earlier PC400 models?
The S6D125-1JJ-FA requires a different pump flow setup compared to the L10 Cummins. Operators note that the L10 units typically have the TVC (Total Volume Control) set near maximum, whereas the S6D125-1JJ-FA TVC is set to the midpoint between minimum and maximum. This adjustment accounts for the different torque curve of the Komatsu engine, which likely peaks at a lower speed than the Cummins. The S6D125-1JJ-FA was introduced to resolve valve train damage caused by the hydraulic pumps overpowering the earlier Cummins engine in the PC400LC-6 series (serial A82000 and up). The Komatsu engine is generally considered more durable for this application, with fewer reports of piston ring failure compared to the Cummins units which often required major service around 4,000 hours. The Komatsu line is noted for smooth operation and fuel efficiency, though some operators suggest the entire machine line is designed to wear out simultaneously if a pump fails, potentially affecting resale value. Have your dealer verify the TVC calibration for your specific machine configuration.
What are the typical undercarriage and wear patterns associated with machines using the S6D125-1JJ-FA engine?
Machines equipped with the S6D125-1JJ-FA engine, such as the D65EX-12 dozer, are available in standard-gauge E/EX straight-tilt-blade configurations and wide-gauge, low-ground-pressure P/PX swamp configurations. The P/PX variants are engineered for heavy production work and soft ground, which influences undercarriage wear patterns. Operators note that Komatsu machines are known for durability, but the line is sometimes criticized for wearing out complete machines simultaneously. If the hydraulic pump fails, the engine is often not far behind. Early dash-6 machines had valve problems, particularly on PC150 and PC120 models, but the S6D125-1JJ-FA is part of a later generation with updated pump and valve combinations. The engine itself is turbocharged and aftercooled, with torque output varying by configuration, generally ranging from 920 Nm (678 lb-ft) to 1100 Nm (811 lb-ft). Have your dealer verify the undercarriage condition against the specific gauge configuration (E/EX vs P/PX) of the machine.
What are the known engine quirks and maintenance issues for the S6D125-1JJ-FA series?
The S6D125-1JJ-FA is a turbocharged and aftercooled diesel engine. A known issue for the S6D125-1 engine series is coolant contamination and water in the crankcase, as reported in service discussions. The engine block, bore, and stroke are shared with the naturally aspirated 6D125E-2A and turbocharged S6D125E-2 variants, but the S6D125-1JJ-FA is distinct in its aspiration and control system. The engine is known for reliability and durability, with some operators stating they ran so long they broke rather than wore out, provided decent maintenance was performed. The shop manual for the 125 Series (including 6D125-1, S6D125, and SA6D125) covers detailed repair procedures and maintenance schedules. Regular maintenance of the fuel filter, oil filter, and turbocharger is critical. Have your dealer verify the condition of the turbocharger and cooling system components.
What are the common electrical or sensor issues reported for this engine platform?
Komatsu equipment fault codes related to the engine controller and sensors include E10 (engine controller power failure/engine management system malfunction), E11 (engine control failure with reduced output power to protect the engine), and E15 (engine sensor malfunction for temperature, fuel, etc.). These codes indicate abnormalities in the engine controller, sensors, valves, pumps, temperature levels, pressure levels, circuits, and solenoid valves. The fault codes list covers issues that could cause decreased output, stalling, overheating, or other issues requiring repair. The S6D125-1JJ-FA is part of the S6D125 series, which includes various sub-models like S6D125-1JJ and S6D125-1KK, each with specific serial ranges. The engine management system is sensitive to sensor inputs, and faults in these areas can lead to significant power reduction. Have your dealer verify the integrity of the engine controller and sensor wiring harnesses.
What fluids and specifications are recommended for the S6D125-1JJ-FA engine?
Komatsu recommends using Komatsu Genuine Lubricants and Coolants, which are formulated to meet the strict Komatsu Engineering Standard. Specific fluid types include diesel engine oil, hydraulic oil, axle oil, powertrain oil, and super-coolant AF-NAC. The engine oil capacity and other fluid capacities are detailed in the operation and maintenance manual for the specific machine model (e.g., D65EX-12). The exact capacity varies by configuration and series. The maintenance schedule includes intervals for replacing fuel filters, oil filters, and oils, ranging from 500 to 2000 hours depending on the component. Use Komatsu EO, TO, AXO, or HO fluids as specified in the machine's operation and maintenance manual. Have your dealer verify the exact fluid capacities for your specific machine configuration.
What are the key specifications and performance characteristics of the S6D125-1JJ-FA engine?
The S6D125-1JJ-FA is a turbocharged and aftercooled diesel engine. Torque output varies depending on the application and configuration, generally ranging from 920 Nm (678 lb-ft) to 1100 Nm (811 lb-ft). The engine is part of the 125 Series, which includes models like 6D125-1, S6D125, and SA6D125. The S6D125-1JJ-FA is used in various Komatsu machines, including dozers and excavators. The engine is known for its reliability, durability, and power. The specific power rating and other performance characteristics depend on the machine application and regional emissions package. The engine serial number is stamped on the engine block, typically on the left side near the injection pump. Have your dealer verify the exact power rating and emissions tier for your specific machine.
What should be checked when buying a used machine with the S6D125-1JJ-FA engine?
When buying a used machine with the S6D125-1JJ-FA engine, verify the engine serial number against the machine plate to ensure it matches the S/N 10001-UP range. Check for signs of coolant contamination or water in the crankcase, a known issue for the S6D125-1 series. Inspect the turbocharger and cooling system components for wear or damage. Review the Komtrax history if available, as it provides independent records of running hours, fault codes, and location. Compare the Komtrax hours against the dashboard reading and dealer-stamped service records; a gap of more than 50 hours may indicate hour-meter rollback. Check the TVC setting and pump flow calibration, as these differ from earlier Cummins-equipped models. Verify the undercarriage condition, especially if the machine is a P/PX low-ground-pressure variant. Have your dealer verify the engine and machine condition before purchase.
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
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