Cummins/Onan 2.5 EGHAA troubleshooting: 150 symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan 2.5 EGHAA — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Symptom | Cause | Remedy |
|---|---|---|
| FAILS TO CRANK | 1. Low battery. 2. Bad battery connection. | 1. Check battery electrolyte level. 2. Clean and tighten all battery and cable connections. |
| CRANKS SLOWLY | 1. Low battery. 2. Bad battery connection. | 1. Check battery electrolyte level. 2. Clean and tighten all battery and cable connections. |
| ENGINE WON’T START | 1. Fuel below genset pickup level in tank. 2. Fuel supply shutoff valve closed. 3. Remove spark plug and clean. 4. Add oil if necessary. | 1. Add fuel. 2. Fully open fuel supply valve. 3. Replace with recommended oil. 4. Disconnect load while starting. |
| EXHAUSTING BLACK SMOKE | 1. Choke stuck. 2. Dirty air filter. 3. Rich fuel mixture. | 1. Open choke 2. Clean or replace air filter. 3. Contact an Onan service center. |
| UNIT RUNS THEN STOPS | 1. Out of fuel. 2. Low oil level. | 1. Add fuel. 2. Add oil. |
| UNIT RUNS THEN SURGES | 1. Loose or worn spark plug lead 2. Faulty spark plug. 3. Dirty fuel filter or generator set at too steep of an angle. 4. Governor out of adjustment or lean fuel mixture. | 1. Check spark plug lead connection. 2. Remove and clean or replace. 3. Check fuel filter and angle of generator set. 4. Contact an Onan service center. |
| NO AC OUTPUT VOLTAGE | 1. Open AC circuit breaker due to an overload. | 1. Remove all loads, reset breaker, check loads for defects. Do not exceed rated load specifications. |
| NO DC OUTPUT VOLTAGE | 1. Open DC circuit breaker due to an overload. | 1. Remove all loads, reset breaker, check for shorted battery or load defects. Do not exceed rated load specifications. |
| Engine misfires | Faulty ignition due to worn or fouled spark plug | Clean or replace spark plug. |
| Engine misfires | Faulty ignition due to faulty ignition system | See Ignition System section. |
| Engine misfires | Faulty ignition due to faulty plug wire | Check spark plug wire and replace if necessary. |
| Engine misfires | Lean fuel mixture due to incorrectly adjusted carburetor | See Carburetor Adjustment section. |
| Engine misfires | Lean fuel mixture due to incorrect float level | Check carburetor float. |
| Engine misfires | Lean fuel mixture due to dirt in carburetor | Disassemble carburetor and clean all passages. |
| Engine misfires | Lean fuel mixture due to vacuum leak | Locate leak, check for loose carburetor. |
| Engine misfires | Contaminated fuel | Drain fuel tank and refill with fresh fuel. |
| Engine misfires | Dirty air cleaner | Clean or replace air cleaner. |
| Engine backfires | Faulty ignition due to worn or fouled spark plug | Clean or replace spark plug. |
| Engine backfires | Faulty ignition due to faulty ignition system | See Ignition System section. |
| Engine backfires | Lean fuel mixture due to incorrectly adjusted carburetor | See Carburetor Adjustment section. |
| Engine backfires | Lean fuel mixture due to incorrect float level | Check carburetor float. |
| Engine backfires | Lean fuel mixture due to dirt in carburetor | Disassemble carburetor and clean all passages. |
| Engine backfires | Lean fuel mixture due to vacuum leak | Locate leak, check for loose carburetor. |
| Engine backfires | Excessive engine wear | E140H engine: See Onan Elite Horizontal engine manual 965-0758; GH170, GH280 engines: See Engine Block Assembly section |
| Engine lacks power | Faulty ignition due to worn or fouled spark plug | Clean or replace spark plug. |
| Engine lacks power | Faulty ignition due to faulty ignition system | See Ignition System section. |
| Engine lacks power | Dirty air cleaner | Clean or replace air cleaner. |
| Engine lacks power | Restricted fuel flow due to plugged | Clean or replace fuel filter. |
| Engine lacks power | Incorrect fuel mixture due to incorrectly adjusted carburetor | See Carburetor Adjustment section. |
| Engine lacks power | Incorrect fuel mixture due to incorrect float level | Check carburetor float. |
| Engine lacks power | Incorrect fuel mixture due to dirt in carburetor | Disassemble carburetor and clean all internal passages. |
| Engine lacks power | Exhaust system blocked or restricted | Locate and remove cause of blockage. |
| Engine lacks power | Incorrect valve clearance or defective valve(s) | Adjust valve clearance/inspect valves; E140H engine: See Onan Elite Horizontal engine manual 965-0758; GH170, GH280 engines: See Engine Block Assembly section |
| Engine lacks power | No load speed set too low | Adjust governor setting. |
| Engine lacks power | Excessive engine wear or damage to engine | E140H engine: See Onan Elite Horizontal engine manual 965-0758; GH170, GH280 engines: See Engine Block Assembly section |
| Engine lacks power | Choke valve blockage or choke lever set incorrectly | Open choke lever fully, if problem continues see Fuel System section. |
| Engine overheats | Restricted air flow due to dirt or debris blocking air inlet or outlet | Clear away any debris that may restrict airflow. |
| Engine overheats | Dirt or oil covering engine cooling fins | Clean away all dirt and oil from engine cooling fins. |
| Engine overheats | Cooling fan plugged or broken | Inspect cooling fan, see Generator Service section. |
| Engine overheats | Lean fuel mixture due to incorrectly adjusted carburetor | See Carburetor Adjustment section. |
| Engine overheats | Lean fuel mixture due to incorrect float level | Check carburetor float. |
| Engine overheats | Lean fuel mixture due to dirt in carburetor | Disassemble carburetor and clean all internal passages. |
| Black exhaust smoke | Rich fuel mixture due to dirty air cleaner | Clean or replace air cleaner. |
| Black exhaust smoke | Rich fuel mixture due to choke closed | Check choke setting. |
| Black exhaust smoke | Rich fuel mixture due to incorrectly adjusted carburetor | See Carburetor Adjustment section. |
| Black exhaust smoke | Rich fuel mixture due to dirt in the carburetor | Disassemble carburetor and clean all internal passages. |
| White or blue exhaust smoke | Lean fuel mixture due to dirty air cleaner | Clean or replace air cleaner. |
| White or blue exhaust smoke | Lean fuel mixture due to incorrect float level | Check carburetor float. |
| White or blue exhaust smoke | Lean fuel mixture due to incorrectly adjusted carburetor | See Carburetor Adjustment section. |
| White or blue exhaust smoke | Lean fuel mixture due to dirt in the carburetor | Disassemble carburetor and clean all internal passages. |
| White or blue exhaust smoke | Clogged or faulty breather | Clean or replace breather. |
| White or blue exhaust smoke | Contaminated fuel | Drain and replace fuel. |
| White or blue exhaust smoke | Excessive engine wear | E140H engine: See Onan Elite Horizontal engine manual 965-0758; GH170, GH280 engines: See Engine Block Assembly section |
| Engine hunts or surges | Sticking or binding governor linkage | Check linkage alignment and straighten or replace. Clean governor linkage. |
| Engine hunts or surges | Incorrect governor adjustment | See Governor section. Also: E140H engine: See Onan Elite Horizontal engine manual 965-0758; GH170, GH280 engines: See Engine Block Assembly section |
| Engine hunts or surges | Faulty governor spring | Replace governor spring. |
| Engine hunts or surges | Incorrect fuel mixture due to incorrectly adjusted carburetor | See Carburetor Adjustment section. |
| Engine hunts or surges | Incorrect fuel mixture due to incorrect float level | Check carburetor float. |
| Engine hunts or surges | Incorrect fuel mixture due to dirt in carburetor | Disassemble carburetor and clean all internal passages. |
| Engine hunts or surges | Governor mechanism worn excessively | E140H engine: See Onan Elite Horizontal engine manual 965-0758; GH170, GH280 engines: See Engine Block Assembly section |
| Engine hunts or surges | Fuel supply problem caused by dirty fuel filter | Clean or replace fuel filter. |
| Engine hunts or surges | Fuel supply problem caused by contaminated fuel supply | Drain and refill fuel supply. |
| Uses too much oil (Note: New engines sometimes use excess oil during break-in) | Oil viscosity is too light or oil is diluted | Drain oil and refill with correct viscosity oil. |
| Uses too much oil (Note: New engines sometimes use excess oil during break-in) | Crankcase breather valve is dirty or defective | Clean crankcase breather or replace if defective. |
| Uses too much oil (Note: New engines sometimes use excess oil during break-in) | Oil leaks | Locate source of leak and repair as required. |
| Uses too much oil (Note: New engines sometimes use excess oil during break-in) | Excessive engine wear | E140H engine: See Onan Elite Horizontal engine manual 965-0758; GH170, GH280 engines: See Engine Block Assembly section |
| Uses too much oil (Note: New engines sometimes use excess oil during break-in) | Light loading | Do not run set at no load for long periods of time. |
| Engine shuts down and will not restart | Low oil level | Add oil as required. |
| Engine shuts down and will not restart | Low oil level switch defective | Replace oil level switch. E140H engine: See Onan Elite Horizontal engine manual 965-0758; GH170, GH280 engines: See Engine Block Assembly section |
| Engine shuts down and will not restart | Fouled spark plug | Clean or replace spark plug. |
| Engine shuts down and will not restart | Faulty fuel system | See Fuel System section. |
| Engine does not crank (electric start models only) | Defective Start/On/Stop switch | Check switch for continuity and replace if defective. |
| Engine does not crank (electric start models only) | Open circuit in wiring between Start/On/Stop switch and starter solenoid or between battery and starter | Check wiring and connections for continuity and repair if defective. |
| Engine does not crank (electric start models only) | Insufficient voltage for cranking due to battery not charged | Check condition of battery and recharge or replace as needed. |
| Engine does not crank (electric start models only) | Insufficient voltage for cranking due to terminal connections loose or dirty | Clean and tighten battery cable connections, starter connections and ground connections. |
| Engine does not crank (electric start models only) | Insufficient voltage for cranking due to defective charge circuit | Check diode and replace if defective. |
| Engine does not crank (electric start models only) | Insufficient voltage for cranking due to defective Ignition Control Unit charge circuit | Refer to Section 6, Engine - Primary Systems for test procedures. |
| Engine does not crank (electric start models only) | Defective starter solenoid or starter | Refer to Section 6, Engine - Primary Systems for test procedures. |
| Engine does not start (recoil start models only) | Defective On/Stop or Engine On/Off switch | Check switch for continuity and replace if defective. |
| Engine does not start (recoil start models only) | Open circuit in wiring between On/Stop or Engine On/Off switch | Check wiring and connections for continuity and repair if defective. |
| Engine does not start (recoil start models only) | Defective Ignition Module | Refer to Section 6, Engine - Primary Systems for test procedures. |
| Engine does not start (recoil start models only) | Low oil level | Check oil level and fill if necessary. |
| Full power switch does not function properly | Defective Full Power switch | Check switch for continuity and replace if defective. |
| Full power switch does not function properly | Wire connections to Full Power switch are not making contact or are miswired | Check for good wire connections and compare connections with wiring diagram in Section 11. |
| Idlematic does not operate (only used on certain models) | Defective Idlematic switch | Check switch for continuity and replace if defective. |
| Idlematic does not operate (only used on certain models) | Wire connections to Idlematic switch, Idlematic Control, or Idlematic Solenoid are not making contact or are miswired | Check for good wire connections and compare connections with wiring diagram in Section 11. |
| Idlematic does not operate (only used on certain models) | Defective Idlematic Solenoid | Check Idlematic solenoid for a binding plunger movement. |
| Idlematic does not operate (only used on certain models) | Defective Idlematic Control | Check to see that the appropriate generator leads pass through the current transformer. Test Idlematic Control. |
| Engine cannot be turned off with switch | Defective Start/On/Stop switch, On/Start switch, or Engine On/Off switch | Check switch for continuity and replace if defective. |
| Engine cannot be turned off with switch | Open circuit in switch wiring | Check wire connections to switch. |
| No AC output voltage (models with automatic voltage regulator) | Open AC circuit breaker | Locate cause of overload and correct as required. Reset breaker. |
| No AC output voltage (models with automatic voltage regulator) | Open circuit between stator main coil and AC receptacle. Defective receptacle. | Check for continuity and correct if circuit is open. Check for defective receptacle. |
| No AC output voltage (models with automatic voltage regulator) | Defective stator main coil | Test stator main coil for open, shorted, or grounded windings and replace if defective. |
| AC output voltage only 6 to 18 VAC (models with automatic voltage regulator) | Defective rotor coil | Test rotor coil for open, shorted, grounded windings and replace if defective. |
| AC output voltage only 6 to 18 VAC (models with automatic voltage regulator) | Defective stator sub coil | Test stator sub coil for open, shorted, or grounded windings and replace if defective. |
| AC output voltage only 6 to 18 VAC (models with automatic voltage regulator) | Faulty brushes or slip rings | Check brushes and replace if defective. Inspect slip rings and clean if needed. |
| AC output voltage only 6 to 18 VAC (models with automatic voltage regulator) | Faulty Voltage Regulator (AVR) | If the rotor and stator test good, and the brush block and slip rings are good, replace the AVR module and recheck. |
| AC output voltage only 6 to 18 VAC (models with automatic voltage regulator) | Faulty permanent magnet in rotor | Replace rotor after checking other possible causes for 6 to 18 VAC. |
| AC output voltage too low or too high (models with automatic voltage regulator) | Engine governor incorrectly adjusted | Check engine speed. Refer to Engine Primary System section. |
| AC output voltage too low or too high (models with automatic voltage regulator) | Faulty voltage regulator (AVR) | Replace the AVR module and recheck. |
| Noisy generator (models with automatic voltage regulator) | Worn rotor shaft bearing | Replace end bearing. |
| Noisy generator (models with automatic voltage regulator) | Rotor and stator rubbing together due to varnish lumps | Check for varnish lumps between rotor and stator and remove as required. |
| Noisy generator (models with automatic voltage regulator) | Rotor and stator rubbing together due to rotor misaligned with crankshaft | Follow specified assembly procedures to correct rotor to crankshaft alignment. |
| Generator overheats (models with automatic voltage regulator) | Generator overloaded due to defective circuit breaker | Replace circuit breaker. Do not exceed specified load when operating set. |
| Generator overheats (models with automatic voltage regulator) | Airflow restricted due to dirt or debris covering vent openings in cover or adapter | Clean away all dirt or debris as required. |
| Generator overheats (models with automatic voltage regulator) | Stator windings covered with oil or dirt | Clean stator windings. |
| Generator overheats (models with automatic voltage regulator) | Defective windings in rotor or stator | Test each component for open, grounded, or shorted windings and replace if defective. |
| Low or no DC output (models with automatic voltage regulator) | Open DC circuit breaker | Locate cause of overload and correct as required. Reset breaker. |
| Low or no DC output (models with automatic voltage regulator) | Open circuit between stator DC coil and diode assembly or between diode assembly and receptacle | Check for continuity and correct if circuit is open. |
| Low or no DC output (models with automatic voltage regulator) | Defective stator DC coil | Test stator DC coil for open, grounded or shorted windings. |
| Low or no DC output (models with automatic voltage regulator) | Defective diode assembly | Test diode assembly for open or short. |
| No AC output voltage (models with capacitor-type voltage regulator) | Open AC circuit breaker | Locate cause of overload and correct as required. Reset breaker. |
| No AC output voltage (models with capacitor-type voltage regulator) | Open circuit between stator main coil and AC receptacle. Defective receptacle. | Check for continuity and correct if circuit is open. Check for defective receptacle. |
| No AC output voltage (models with capacitor-type voltage regulator) | Defective stator main coil | Test stator main coil for open, shorted, or grounded windings and replace if defective. |
| AC output voltage only 3 to 18 VAC (models with capacitor-type voltage regulator) | Defective stator sub coil | Test stator sub coil for open, shorted, or grounded windings and replace if defective. |
| AC output voltage only 3 to 18 VAC (models with capacitor-type voltage regulator) | Defective rotor coil or defective rotor winding diode | Test rotor coil for open, shorted, or grounded winding and defective diode. Replace rotor if defective. |
| AC output voltage only 3 to 18 VAC (models with capacitor-type voltage regulator) | Open or shorted capacitor | Test capacitor for open or short and replace if defective. |
| AC output voltage too low or too high (models with capacitor-type voltage regulator) | Engine governor incorrectly adjusted | Refer to Engine Primary System section. |
| Noisy generator (models with capacitor-type voltage regulator) | Worn rotor shaft bearing | Replace end bearing. |
| Noisy generator (models with capacitor-type voltage regulator) | Rotor and stator rubbing together due to varnish lumps | Check for varnish lumps between rotor and stator and remove as required. |
| Noisy generator (models with capacitor-type voltage regulator) | Rotor and stator rubbing together due to rotor misaligned with crankshaft | Follow specified assembly procedures to correct rotor to crankshaft alignment. |
| Generator overheats (models with capacitor-type voltage regulator) | Generator overloaded due to defective circuit breaker | Replace circuit breaker. Do not exceed specified load when operating set. |
| Generator overheats (models with capacitor-type voltage regulator) | Airflow restricted due to dirt or debris covering vent openings in cover or adapter | Clean away all dirt or debris as required. |
| Generator overheats (models with capacitor-type voltage regulator) | Stator windings covered with oil or dirt | Clean stator windings. |
| Generator overheats (models with capacitor-type voltage regulator) | Defective windings in rotor or stator | Test each component for open, grounded, or shorted windings and replace if defective. |
| Low or no DC output (models with capacitor-type voltage regulator) | Open DC circuit breaker | Locate cause of overload and correct as required. Reset breaker. |
| Low or no DC output (models with capacitor-type voltage regulator) | Open circuit between stator DC coil and diode assembly or between diode assembly and receptacle | Check for continuity and correct if circuit is open. |
| Low or no DC output (models with capacitor-type voltage regulator) | Defective stator DC coil | Test stator DC coil for open, grounded or shorted windings. |
| Low or no DC output (models with capacitor-type voltage regulator) | Defective diode assembly | Test diode assembly for open or short. |
| Engine cranks slowly (electric start models) | Low battery | Check battery electrolyte level and charge |
| Engine cranks slowly (electric start models) | Bad battery connection | Clean and tighten all battery and cable connections |
| Engine cranks slowly (electric start models) | Oil is too heavy | Replace with lighter oil |
| Engine cranks slowly (electric start models) | Load is connected | Always disconnect load while starting |
| Engine won't start | Out of fuel | Add fuel |
| Engine won't start | Fuel supply valve closed | Fully open fuel supply valve |
| Engine won't start | Carbon deposits on spark plug | Remove and clean or replace spark plug |
| Engine won't start | Low oil level | Add oil as necessary |
| Engine won't start | Loose or worn spark plug lead | Check spark plug lead connection |
| Engine won't start | Faulty spark plug | Remove and clean or replace spark plug |
| Engine won't start | Dirty fuel filter or generator set at too steep of an angle | Check fuel filter and generator set angle |
| Engine won't start | Governor out of adjustment or lean fuel mix | Contact an Onan service center |
| Exhausting black smoke | Choke closed | Open choke |
| Exhausting black smoke | Dirty air filter | Clean or replace air filter |
| Exhausting black smoke | Rich fuel mixture | Contact an Onan service center |
| Unit runs then stops | Open DC circuit breaker due to an overload | Remove all loads, reset circuit breaker, check for an overload or shorted battery. Do not exceed generator set rated load specifications |
| Unit runs but surges | Out of fuel | Add fuel |
| Unit runs but surges | Low oil level | Add oil |
| Unit runs but surges | Excess oil | Reduce oil level |
| No AC output voltage | Open AC circuit breaker due to an overload | Remove all loads, re-set circuit breaker, check tools or appliances being used for defects. Do not exceed generator set rated load specifications |
| No DC output voltage | Open DC circuit breaker due to an overload | Remove all loads, reset circuit breaker, check for an overload or shorted battery. Do not exceed generator set rated load specifications |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Faulty ignition due to worn or fouled spark plug; Faulty ignition due to faulty ignition system; Dirty air cleaner; Restricted fuel flow due to plugged. See the table for the matching fixes.
Documented causes: Faulty ignition due to worn or fouled spark plug; Faulty ignition due to faulty ignition system; Faulty ignition due to faulty plug wire; Lean fuel mixture due to incorrectly adjusted carburetor. See the table for the matching fixes.
Documented causes: Sticking or binding governor linkage; Incorrect governor adjustment; Faulty governor spring; Incorrect fuel mixture due to incorrectly adjusted carburetor. See the table for the matching fixes.