Komatsuengine(no series)

Komatsu SA6D125-1Q(S/N 28389-UP)

Maintenance schedule, common problems & OEM parts breakdown

The Komatsu SA6D125-1Q is a turbocharged, aftercooled diesel engine belonging to the 125 Series, manufactured from approximately 2011 onward. It powers mid-to-heavy class construction equipment, including the PC400-6 and WA470-3, with operating weights ranging from 34,000 to 52,000 lb (15,422 to 23,587 kg). The engine delivers 275 hp (205 kW) and 1,010 lb-ft (1,370 Nm) of torque. It succeeded the naturally aspirated 6D125-1 and was later replaced by the SAA6D125E-2 series to meet Tier 4 Final emissions standards.

The SA6D125-1Q remains critical in the used and parts market due to its widespread installation in the PC400-6 and WA470-3 platforms. Its robust block design and hardened liners allow for extended service life, making it a preferred choice for remanufacturing. The engine's compatibility with Komatsu's KOWA fluid analysis program and KOMTRAX telematics ensures predictable maintenance, sustaining high residual value for machines equipped with this powertrain.

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 SA6D125-1Q(S/N 28389-UP) specifications

Engine

ModelSA6D125-1Q
Series125 Series (125-1)
ConfigurationTurbocharged, Aftercooled Diesel
Displacement11 L (672 cu in)
Cylinders6
Gross Power275 hp (205 kW)
Torque1,010 lbf·ft (1,370 N·m)
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
Dig/Dump/LiftNot documented for this exact serial range — verify with your dealer

Service capacities (summary)

Fuel TankNot documented for this exact serial range — verify with your dealer
Hydraulic SystemNot documented for this exact serial range — verify with your dealer
Engine OilNot documented for this exact serial range — verify with your dealer
Cooling SystemNot 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 SA6D125-1Q(S/N 28389-UP) maintenance schedule

Service intervalTasks
Every 10 h
  • Check engine oil level.
  • Check coolant level.
  • Inspect for fuel, oil, and coolant leaks.
  • Drain water separator from fuel tank.
Every 250 h
  • Change engine oil.
  • Replace engine oil filter.
  • Replace fuel filter.
  • Replace air cleaner element.
Every 500 h
  • Inspect hydraulic oil level.
  • Inspect hydraulic return filter.
  • Inspect swing bearing grease.
  • Inspect undercarriage tension.
Every 1,000 h
  • Change hydraulic oil.
  • Replace hydraulic return filter.
  • Inspect turbocharger hoses.
  • Inspect exhaust manifold bolts.
Every 2,000 h
  • Change coolant.
  • Replace coolant filter.
  • Inspect injector lines.
  • Inspect fuel injection pump.
Every 4,000 h
  • Inspect valve clearance.
  • Inspect piston rings.
  • Inspect cylinder liner wear.
  • Inspect crankshaft bearings.

Servicing the SA6D125-1Q(S/N 28389-UP) beyond the schedule

Predictive Maintenance & Fluid Analysis

Utilize Komatsu Oil/Wear Analysis (KOWA) at every 500-hour interval to monitor engine wear metals and coolant condition. The SA6D125-1Q's hardened cylinder liners and high-pressure Bosch-style fuel system require strict adherence to Komatsu EO/TO diesel engine oil specifications. Analyze fuel dilution levels to detect piston ring wear early. Track coolant pH and inhibitor levels to prevent cavitation erosion in the SA6D125-1Q's wet liner design. Use KOMTRAX telematics to correlate load frequency with fluid degradation rates for optimized change intervals.

Corrective & Common Repairs

Address intermittent starting or random shutdowns by inspecting the engine controller power supply and sensor wiring harnesses. Replace faulty coolant temperature or intake air temperature sensors if fault codes CA144, CA153, or CA154 appear. Repair fuel leaks at injector lines by replacing copper sealing washers and tightening to factory torque. Inspect the turbocharger compressor wheel for shaft play and replace if excessive. Clean the aftercooler core to restore airflow and prevent overheating under heavy load.

Overhaul & Rebuild Points

Perform an in-frame overhaul at 10,000 hours or when compression drops below specification. Replace piston rings, cylinder liners, and bearings using the Komatsu SA6D125 overhaul kit. Inspect the crankshaft for journal wear and grind if necessary. Replace the fuel injection pump if fuel delivery pressure fails to meet standards. Rebuild the turbocharger with new bearings and seals. Verify valve clearance and adjust tappets to specification during the overhaul process.

Seasonal & Environment Servicing

In cold climates, use Komatsu Super-coolant AF-NAC rated for -35°C to prevent freezing and ensure proper heat transfer. Install block heaters and oil pan heaters for temperatures below -10°C. In dusty environments, inspect the air cleaner indicator more frequently and replace the primary and secondary elements as needed. Drain the fuel water separator daily to prevent microbial growth in humid conditions. Inspect the radiator and aftercooler fins for debris buildup to maintain optimal cooling efficiency.

SA6D125-1Q(S/N 28389-UP) common service parts

Part numberPart
07281-00197Clamp,(With Pre-Fuel Filter)Check fitment →
600-311-8291Cartridge,Fuel FilterCheck fitment →
6114-71-6200Fuel Filter Ass'YCheck fitment →
6114-71-6210Head, Fuel FilterCheck fitment →
6125-81-7032Element Ass'Y,Air CleanerCheck fitment →

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SA6D125-1Q(S/N 28389-UP) fault codes & troubleshooting

CodeMeaningLikely causeWhat to do
CA115Engine crankshaft speed sensor failureBroken sensor, wiring issue, or connector corrosionReplace the speed sensor and verify the voltage at the pin connector
CA111Internal engine controller faultECM internal abnormalityReplace or reprogram the ECM
CA441Battery voltage too lowAlternator or battery failureReplace the alternator or battery and check the voltage regulator
CA442Battery voltage too highAlternator or voltage regulator failureReplace the alternator or battery and check the voltage regulator
CA122Intake air pressure sensor high voltageSensor malfunction or wiring issueVerify the intake pressure sensor and wiring
CA123Intake air pressure sensor low voltageSensor short or airflow restrictionCheck for a sensor short or an airflow restriction
CA153Intake air temperature sensor high voltageSensor malfunctionReplace or test the IAT sensor
CA154Intake air temperature sensor low voltageSensor malfunctionReplace or test the IAT sensor
CA451Common rail pressure sensor feedback value too highFuel rail sensor malfunction or actual overpressure conditionDiagnose the fuel rail pressure sensor or pump lines
CA452Common rail pressure sensor feedback value too lowFuel rail sensor malfunction or low pressure conditionDiagnose the fuel rail pressure sensor or pump lines

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

SA6D125-1Q(S/N 28389-UP) attachments & work tools

Bulldozer Blade Configurations

The SA6D125-1Q engine (S/N 28389-UP) is factory-equipped in the D135A-2 dozer series. Typical blade options for this class include semi-U (SU) and universal (U) configurations, with capacities varying by configuration/series based on the specific dozer model assignment.

Excavator Bucket Families

This engine powers the PC400LC-3 series excavators. Standard work tools include heavy-duty rock buckets and general-purpose earthmoving buckets. Capacities vary by configuration/series depending on the specific bucket width and depth selected for the PC400LC-3 frame.

Wheel Loader Bucket Types

The SA6D125-1Q is associated with the WA470-3 wheel loader model. Primary work tools include general-purpose (GP) buckets for earthmoving and rock buckets for heavy excavation. Bucket capacities vary by configuration/series to match the loader's lift arm geometry and hydraulic flow.

Hydraulic Coupler/Mounting Systems

Excavator and loader attachments utilize Komatsu’s standard quick coupler systems designed for the PC400 and WA470 frame mounting points. Dozer blades are mounted via the dozer’s proprietary lift arm and blade pin interfaces, requiring specific guarding for the hydraulic lines.

Hydraulic Kit Requirements

High-flow attachments such as heavy-duty breakers or large-diameter augers require auxiliary hydraulic kits. These kits typically include high-flow solenoid valves and reinforced hose assemblies to match the engine’s hydraulic pump output specifications.

Factory Guarding Options

Factory configurations often include heavy-duty undercarriage guards for dozers and rock shields for loader buckets. Excavator models may offer factory-installed rock guards for the boom and stick to protect hydraulic cylinders and hoses in abrasive environments.

All SA6D125-1Q(S/N 28389-UP) assemblies by section

Every catalogued assembly group for the Komatsu SA6D125-1Q(S/N 28389-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Cooling System
Komatsu : Sa6d125-1q(S/N 28389-Up) : Cooling System : Cooling Fan And V-Belt
04***78V-Belt Set,(Ec. Noise Suppression Spec.)1
60***60Fan,Cooling1
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cooling System : Corrosion Resistor And Piping
01***20Bolt,(For Quick Shift) (Mitsubishi)1
01***25Bolt,(For Canvas Canopy?Head Guard)4
01***08Nut,(For Canvas Canopy?Head Guard)1
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cooling System : Tension Pulley
01***16Bolt (Welded)4
01***25Bolt,(For Canvas Canopy?Head Guard)2
01***95Bolt,(For 2nd Travel Speed) (Op)2
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cooling System : Water Bypass Piping
01***20Bolt,(For Quick Shift) (Mitsubishi)1
01***25Bolt,(For Canvas Canopy?Head Guard)1
01***30Bolt,(For Quick Shift) (Mitsubishi)2
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cooling System : Water Pump
01***16Bolt (With Air Heater & Conditioner)6
01***30Bolt,(For Quick Shift) (Mitsubishi)4
01***10Bolt, Fan Mounting3
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Cylinder Block
Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Block : Camshaft
01***22Bolt2
04***25Key, Plain Woodruff1
04***12Ring,Snap (For Ripper)12
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Block : Crankshaft
01***45Bolt6
01***80Screw1
01***85Screw5
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Block : Cylinder Block
01***12Bolt,(Without Air Compressor Type)2
01***45Washer,(For Travel Motor) (Not Show)14
04***14Pin, Dowel2
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Block : Cylinder Block Cover
01***16Bolt (With Air Heater & Conditioner)1
01***25Bolt,(For Canvas Canopy?Head Guard)2
01***00Bolt, Mount Back-Up Alarm2
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Block : Flywheel And Flywheel Housing
01***50Bolt2
01***50Bolt, Radiator To Frame4
01***50Bolt8
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Block : Front Cover And Gear
Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Block : Oil Pan
01***25Bolt,(For Canvas Canopy?Head Guard)31
01***30Bolt,(For Quick Shift) (Mitsubishi)7
01***16Washer,Radio Controlled Slag Handling37
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Block : Piston And Connecting Rod
02***13Pin, Dowel2
04***18Ring, Snap12
61***32Piston Ring Ass'Y6
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Block : Power Take Off
01***30Bolt,(For France Noise Suppression)5
01***35Bolt, Mounting - Flywheel Housing End2
01***30Bolt,Radio Controlled Slag Handling12
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Cylinder Head
Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Head : After Cooler Piping
01***20Bolt,(For Quick Shift) (Mitsubishi)2
01***25Bolt,(For Canvas Canopy?Head Guard)1
01***35Bolt,(For Quick Shift) (Mitsubishi)4
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Head : Air Cleaner
01***25Bolt,(For Canvas Canopy?Head Guard)4
01***40Bolt, Mount Master Brake Cylinder4
01***35Bolt, Mount Bracket To Floor2
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Head : Air Intake Manifold And After Cooler
01***10Bolt,(With Auto Emergency Steering)2
01***90Bolt, Priority Valve Mounting2
01***25Bolt,(For Canvas Canopy?Head Guard)2
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Head : Cylinder Head
04***20Pin,Dowel (Welded)2
61***30Sleeve,Holder1
61***20Cotter, Valve48
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Head : Exhaust Manifold And Turbocharger
01***80Bolt, Mount Strainer Flange2
01***00Bolt (M10-1.50x100)16
01***45Screw4
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Head : Muffler
01***40Bolt,(Dust And Dirt Protection)4
01***55Bolt,(For Suction? Reversible Fan)4
01***30Bolt,Radio Controlled Slag Handling4
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Head : Rocker Arm And Housing
01***95Bolt,(For 2nd Travel Speed) (Op)2
01***08Nut,R.H. Thread12
01***16Washer,(With Shoe Slip Control)34
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Head : Rocker Arm Housing Cover
01***16Washer,Radio Controlled Slag Handling24
61***11Cover,Head? No.2?3?4?5?66
61***10Gasket,Cylinder Head Cover6
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Head : Turbocharger
61***00Turbocharger Ass'Y,(Tv7705)1
GA***07Rotor Ass'Y1
GA***85V-Band1
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Cylinder Head : Water Manifold And Thermostat
02***43O-Ring,Water Manifold6
07***12Washer, Gasket,(Without Thermo Sensor) (K1)1
07***15Plug,(Used When Without Heater)1
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Electrical System
Komatsu : Sa6d125-1q(S/N 28389-Up) : Electrical System : Alternator (35a)
60***60Alternator A. (35a)1
KD***57Bearing,Ball? Front1
KD***60Pulley,Non Hardening1
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Electrical System : Alternator And Mounting
01***35Bolt,(For Quick Shift) (Mitsubishi)1
01***30Bolt1
01***23Washer,(A)(W/After Cooler)(S6d155-4b)2
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Electrical System : Starting Motor (7.5kw)
60***10Starting Motor Ass'Y,(7.5kw)1
KD***20Magnetic Switch Assembly1
KD***40Spring,Spring4
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Electrical System : Starting Motor And Mounting
01***45Bolt,(For Travel Motor) (Not Show)3
01***45Washer, Spring3
60***20Clip,(Large Capacity Type)1
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Fuel System
Komatsu : Sa6d125-1q(S/N 28389-Up) : Fuel System : Fuel Filter And Piping
01***16Bolt - Starting Motor Ground Cable1
01***25Bolt, Mount Engine Oil Drain To Fuel Tank5
01***08Nut,See Fig. K4010-04a01
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Fuel System : Fuel Injection Pump (Coupling)
DK***00Coupling,Cross1
DK***60Coupling Ass'Y1
DK***00Nut2
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Fuel System : Fuel Injection Pump (Feed Pump)
DK***20Bolt, Joint1
DK***00Valve,Check2
DK***30Eye,Joint1
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)
DK***20Flyweight Ass'Y1
DK***00Shim? 2.00mm,(High Altitude Spec.)0
DK***00Nut,Lock1
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)
DK***80Shim? 0.5mm0
DK***00Washer,Spring1
DK***00Nut,Cap1
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Fuel System : Fuel Injection Pump (Pump)
61***30Injection Pump A1
DK***30Bearing,Roller2
DK***00Bearing, Center1
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Fuel System : Fuel Injection Pump And Piping
01***30Bolt4
01***25Bolt,(For Canvas Canopy?Head Guard)6
01***30Bolt,(For Quick Shift) (Mitsubishi)4
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Fuel System : Fuel Nozzle And Spill Pipe
01***45Bolt, Divider Valve Mounting12
07***65O-Ring,Cylinder Block6
07***12Gasket,Mechanical Pump Piping2
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Lubricating Oil System
Komatsu : Sa6d125-1q(S/N 28389-Up) : Lubricating Oil System : Lubricating Oil Cooler
01***35Bolt,(For Quick Shift) (Mitsubishi)12
01***40Bolt, Mount Master Brake Cylinder1
01***75Bolt,(For Adjusting)2
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Lubricating Oil System : Lubricating Oil Filter
01***30Bolt - Lower Oil Cooler Outlet Tubemounting4
02***16Plug1
04***12Ring, Snap1
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Lubricating Oil System : Lubricating Oil Piping
01***50Bolt,(With Service Valve R.H.)4
01***16Washer,Radio Controlled Slag Handling7
04***12Ring, Snap1
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Lubricating Oil System : Lubricating Oil Pump And Suction Pipe
01***25Bolt,(Without Auto Priming System)4
01***20Bolt,(Large Capacity Type) (Std)2
01***25Bolt,(Sandy? Dusty Terrain Spec.)5
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Lubricating Oil System : Pto Lubricating Oil Piping
01***25Bolt,(For Canvas Canopy?Head Guard)2
07***12O-Ring, Between Valve And Pump1
07***12Gasket,(Without Air Compressor Type) (K2)6
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Komatsu : Sa6d125-1q(S/N 28389-Up) : Lubricating Oil System : Turbocharger Lubricating Oil Piping
01***20Bolt,(For Quick Shift) (Mitsubishi)4
01***30Bolt,(For Quick Shift) (Mitsubishi)2
01***55Bolt, Mount Tube To Switch Pump1
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Tool And Kit
Komatsu : Sa6d125-1q(S/N 28389-Up) : Tool And Kit : Gasket Kit
01***23Washer,(Not Shown)1
02***43O-Ring,Water Manifold6
07***12O-Ring, Between Valve And Pump1
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SA6D125-1Q(S/N 28389-UP) serial number reference

The engine serial number plate is located on the left side of the engine block, typically near the injection pump or on a metal plate affixed to the valve cover. Read the prefix to identify the engine model (SA6D125-1Q) and the subsequent digits to confirm the serial number falls within the 28389-UP range for correct parts identification.

PrefixIdentifies
SA6D125-1QEngine Model

Frequently asked questions

What is the engine model for the Komatsu SA6D125-1Q(S/N 28389-UP)?

The engine model is the Komatsu SA6D125-1Q, a turbocharged, aftercooled diesel engine from the 125 Series.

What is the operating weight of the machine powered by this engine?

Operating weight varies by configuration and series, typically ranging from 34,000 to 52,000 lb (15,422 to 23,587 kg) for equipment like the PC400-6 and WA470-3.

What engine replaced the SA6D125-1Q?

The SA6D125-1Q was replaced by the SAA6D125E-2 series to meet Tier 4 Final emissions standards.

What SA6D125-1Q(S/N 28389-UP) owners discuss

How does the SA6D125-1Q engine compare to the Cummins L10 in terms of torque and durability?
The SA6D125-1Q provides significantly higher torque than the Cummins L10, allowing it to pull hydraulic pump loads without stalling. The SA6D125-1Q uses hardened liners, high-alloy piston rings, and a Bosch-style fuel system with injection pressures of 3,200 PSI. In contrast, the Cummins L10 used soft liners and a PT fuel system with injection pressures of only 2,100 PSI. Cummins L10 engines in this application class are prone to piston ring failure around 4,000 hours, whereas the Komatsu design is considered more robust for heavy hydraulic loads. Have your dealer verify the specific engine model plate to confirm the SA6D125-1Q designation before comparing performance specs.
What are the typical powertrain and hydraulic behaviors associated with this engine series?
The SA6D125-1Q is a turbocharged, aftercooled diesel engine with 11 liters of displacement and six cylinders. It delivers approximately 275 horsepower (205 kilowatts) and 1,370 Newton meters (1,010 pound-feet) of torque. Fuel consumption at rated power is approximately 70 liters per hour (18.5 gallons per hour). The engine is designed to drive high-capacity hydraulic pumps; if the hydraulic pump fails or becomes overloaded, the engine is at high risk of subsequent damage. The machine operates smoothly and efficiently, but hydraulic weakness when hot often indicates internal pump or valve leakage rather than engine failure.
What undercarriage and wear patterns are typical for machines powered by this engine?
Machines equipped with the SA6D125-1Q (such as the D135A-2 dozer) are heavy earthmoving units subject to significant undercarriage stress. Common wear patterns include rapid degradation of track pads, bushings, and bearings due to continuous load and environmental debris. Track tensioners frequently require adjustment due to mud packing or component stretch. Worn bushings lead to increased vibration and noise. The line is often described as wearing out complete machines simultaneously; therefore, undercarriage inspection should be paired with hydraulic and engine health checks, as failure in one area often precedes failure in others.
What are the common electrical and sensor issues for this engine series?
Komatsu excavators and dozers with this engine rely on electronic control systems. Common issues include intermittent starting, dashboard display failures, and random shutdowns triggered by faulty sensors or unstable power supplies. Multiple fault codes often point to battery issues, poor chassis grounds, or connector corrosion rather than engine mechanical failure. Owners report that a single faulty sensor can trigger cascading warning signals. Always check battery state of charge and main starter cables before assuming electronic control unit failure.
What is the most common cause of engine overheating in this configuration?
Overheating is typically caused by restricted airflow through the cooling package rather than internal engine failure. The primary suspects are debris packed between the radiator, hydraulic oil cooler, charge-air cooler, and air-conditioning condenser. Coolant level drops or system pressurization shortly after a cold start may indicate a deeper engine issue, but marginal cooling capacity is more common. If temperature rises during heavy work but falls at idle, the cooling system is likely restricted. Clean the spaces between heat exchangers regularly.
What should be checked first if the engine loses power under digging load?
Check air filters, fuel filters, fuel tank venting, and intake hoses for restrictions. Verify that the engine RPM remains stable when hydraulics are engaged. If engine speed drops heavily when hydraulic functions are used, the hydraulic system is placing excessive load on the engine or the engine cannot produce expected power. If engine speed remains normal but movements are weak, the hydraulic system is the primary suspect. Do not replace the hydraulic pump immediately; diagnose whether the engine is dragging down the hydraulics or vice versa.
What to check when buying a used machine with the SA6D125-1Q engine (S/N 28389-UP)?
Verify the engine serial number plate on the left side of the engine to confirm the SA6D125-1Q designation (S/N 28389-UP) and distinguish it from earlier 6D125 or S6D125 variants. Inspect the breather for excessive oil blow-by, which may indicate piston ring wear. Check for hydraulic weakness when hot, which signals internal pump or valve leakage. Inspect the undercarriage for worn track pads and bushings. Test the machine under load to ensure the engine does not stall or lose RPM excessively. Have your dealer verify the exact serial range specifications and installed attachment package before purchase.

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

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