Cummins/Onan C Series troubleshooting: 59 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan C Series — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Code | Meaning |
|---|---|
| 31 | Engine will not shut off |
| 38 | Excessive engine moisture |
| 86 | Excessive fuel consumption |
| 387 | Excessive vibration |
| 80 | Exhaust smoke excessive under load |
| 338 | Knock |
| 29 | Fuel or oil leaking from exhaust manifold |
| 35 | Low power |
| Symptom | Cause | Remedy |
|---|---|---|
| Warm Engine | Injection Pump Set too low idle screw setting. | Replace pump. Check/adjust low idle speed screw. |
| Air in Fuel System | Bleed fuel system. See Authorized Repair Facility and check for suction leaks. | |
| Injection Timing incorrect | Check/correct injection timing. | |
| Injector Nozzles Plugged or Inoperative | Replace injectors. | |
| Broken Engine Mounts | Replace mounts. | |
| Wrong High Pressure Lines | Install correct lines. | |
| Engine Surges at Idle | Low Fuel Level in the supply tank. | Fill supply tank. Check/adjust low idle speed screw. |
| Air in the Fuel System | Bleed fuel system and check for suction leaks. | |
| Restricted Fuel Supply | Clean or replace pre-filters and screens and check fuel lines for restriction. | |
| Injection Pump Malfunctioning or Worn | Remove pump. Have pump recalibrated or replace pump. | |
| Lubricating Oil Pressure LOW | External leak at rear & cylinder head, along fuel pump side of block, oil coder cover and gear house. | Add or drain engine oil. Check for external leak. |
| Incorrect Oil Level | Viscosity Low | Refer to coolant temperature above normal range. Change oil if necessary. |
| Oil Filter Plugged | Change oil and replace filter. | |
| Oil Diluted with Coolant (anti-Freezé) | Air in the crankcase, cylinder block freed gasket, cracked block and bad torque leaks. | Change oil. Inspect Turbocharger, leaking oil from outlet. |
| Lubricating Oil Pressure Too High | Malfunctioning pressure switch/gage. | Verify the pressure switch/gage is functioning correctly. |
| Engine Running Too Cold | Check/replace thermostat. Check fan sensor. | |
| Oil Viscosity Too Thick | Make sure the correct oil is being used. | |
| Relief Valve Stuck Closed or Broken Spring | Check/replace valve. | |
| Lube Oil Loss | Visually inspect for oil if equipped, air compressor pumping oil. | Check/replace air compressor. Check the breather tube area for signs of oil loss. Measure blowby and perform required repairs. |
| Crankcase Overfilled | Incorrect oil level is marked on dipstick. | Check if correct. OK |
| Incorrect Oil Specifications or Viscosity | Make sure the correct oil specifications are being used. | |
| Coolant Temperature Above Normal | Low coolant level. | Add coolant. Check fan sensor. |
| Radiator or Cab Heater Leaking | Visually inspect the radiator, heater, hoses and connections to locate the leak. | |
| External Engine Leak | Visually inspect the engine and components for seal or gasket leaks. | |
| Overheating or Leaking Compression Gases Resulting in Loss Through the Radiator Overflow | Review operation for overheating and low power. Refer to troubleshooting logic for coolant temperature above normal. | |
| Coolant Temperature Below Normal | - | Authorized Repair | Radiator Shutters Stuck Inspect the shutters —p| See iz i iti eos repair or replace if Facility in Open Position penecessary. |
| Fan Malfunction | Check/clean sensor and Tempettincion [=~] eodant passage OK | |
| Temperature Gauge Malfunction | Test/replace sensor. Test the gauge - Temperature Gauge |. .- 4 repair or replace Malfunction ff necessary. | |
| Thermostats Incorrect or Malfunctioning | Check thermostats | Thermostats Incorrect or |. - . 4 and replace if 6 Malfunctioning necessary. | |
| Contaminated Coolant | Drain and Flush the Witod Corics tree |__| Cooling System. Fill with of Antifreeze and Water Correct Mixture of Anti- freeze and Water. OK | |
| Oil Leaks from Oil Cooler, Head Gasket, or Head | Check/Replace Oil Cooler. If Equipped, Leaking }---4 Refer to Equipment Transmission Oil Cooler Manufacturer's Procedures) OK | |
| Coolant in the Oil | See Troubleshooting Logic for Coolant Loss Contaminated Coolant Cause Correction ‘ Drain and Flush the Witod Corics tree |__| Cooling System. Fill with of Antifreeze and Water Correct Mixture of Anti- freeze and Water. OK | |
| Excessive Oil Sludge | Review Oil and Filter Change Intervals. OK | |
| Worn Injection Pump Plunger | Replace the Pump. OK | |
| Fuel in the Oil, Engine Operating Too Cold Resulting in Excessive Idling | See Troubleshooting Logic for Coolant Loss Contaminated Coolant Cause Correction ‘ Drain and Flush the Witod Corics tree |__| Cooling System. Fill with of Antifreeze and Water Correct Mixture of Anti- freeze and Water. OK | |
| Lift Pump Seal Leaking | Replace Lift Pump. OK | |
| Malfunctioning Injector | Locate and Replace Malfunctioning Injector. OK | |
| Intake Air Restriction | Check/Replace Filter OK | |
| Excessive Idling | Review Operation for Injector Needle Valve Stuck Open Locate and Replace Malfunctioning Injector. OK | |
| Obstructed Turbocharger Drain Line | Check/Clean Line. OK | |
| Turbocharger Seals Leaking Oil | Check/Replace Turbocharger. OK | |
| Exhaust Smoke Excessive Under Load | More Than One Seal Remove extra i i lower gear. ——pl Washer Under Injector [~~ + washers. Lugging Engine aad Use lower g Under OK | |
| Fuel Quality Poor | OK | |
| Fuel Supply Restricted | Change the fuel filter and check fuel line, pre-filter and screens for restrictions. OK | |
| Injection Fume Timing Incorrectly Adjusted High Speed Screw | Check/adjust high speed screw. OK | |
| Low Power (Vehicle Overloaded) | Reduce load or use pes lower gears. OK | |
| Lubricating Oil Level Too High | Drain oil to proper level. OK | |
| Throttle Linkage Adjustment Wrong Travel of the Fuel Control Lever | Check and adjust throttle linkage for full travel of the fuel control lever. OK | |
| Intake or Exhaust System Restricted | Check intake and exhaust systems for restrictions. Inspect air filter and replace as necessary. Turbocharger and Intake Manifold OK | |
| Air Fuel Control Tube Leaking and/or Restricted | Tighten fittings. and/or ---4 Replace tube if Restricted necessary. OK | |
| Air Leak Between Turbocharger and Exhaust Manifold | Correct leak. OK |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Injection Pump Set too low idle screw setting.. See the table for the matching fixes.
Documented causes: Low Fuel Level in the supply tank.. See the table for the matching fixes.
Documented causes: External leak at rear & cylinder head, along fuel pump side of block, oil coder cover and gear house.. See the table for the matching fixes.