Cummins/Onan QG 4000 troubleshooting: 14 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan QG 4000 — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Symptom | Cause | Remedy |
|---|---|---|
| Crank but won’t start | 1. Fuel below generator pickup level in tank. 2. Fuel supply shutoff valve closed. 3. Carbon deposits on spark plug(s). 4. Low oil level. | |
| Exhausting black smoke | 1. Dirty air filter. 2. Choke stuck or misadjusted. | |
| Unit runs then stops, or stops when driving around a corner | 1. Low fuel level. 2. Low oil level. 3. Excess oil. | |
| Unit starts and runs, then stops when the start switch is released | 1. Low fluid levels. 2. Possible overheating. 3. Other functional problem. | |
| Unit runs then surges | 1. Loose or worn spark plug leads. 2. Defective ignition coil, wiring, or control components. 3. Faulty spark plug. 4. Governor out of adjustment. 5. Combustion air pre-heat malfunction. 6. Carburetor icing. 7. Carburetor varnishing. | |
| Circuit breaker trips | 1. Overloaded circuit. | |
| No electric output | 1. Tripped circuit breaker. 2. Other function problem. | |
| Fails To Crank | Low battery. | Check battery fluid level and charge or replace the battery if necessary. |
| Cranks slowly | Low battery. | Check battery voltage at generator. Bad battery connection. Clean and tighten all battery cable connections. Incorrect oil viscosity. Replace with recommended viscosity oil. |
| Cranks but won’t start | Fuel below generator pickup level in tank. | Add fuel. Carbon deposits on spark plug(s). Remove spark plug(s) and replace. Low oil level. Add oil. |
| Air conditioner thermal overload | Due to thermal overload | The air conditioner thermal overload will reset itself after the compressor cools. Some, but not all RV air conditioner thermostats have built-in time delays to prevent short-cycling. |
| Short-cycling of air conditioner | When the thermostat is mounted so that cold air blows directly on it | Direct the flow of air from the air conditioner away from the thermostat or relocate the thermostat. You can prevent air conditioner short-cycling by always ensuring the air conditioner rests for 3–4 minutes after the compressor shuts off before trying to restart it. |
| Generator overload | Shut down the generator due to overload; or trip the circuit breakers on the generator or the main electrical panel will stop the flow of power. Turn off all appliances before resetting the breaker. If the breaker trips again with all electrical loads off, you may have a short circuit in your wiring. | |
| Generator surging | Changes in generator engine speed (called surging) can damage appliances in your RV; caused by inadequate fuel supply, lack of exercise and poor maintenance. | Ensure adequate generator fuel supply. Follow the generator exercise recommendations or the out-of-service protection recommendations outlined in your operator’s manual. Contact your local Cummins authorized RV service and parts dealer to diagnose fuel supply problems. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Low battery.. See the table for the matching fixes.
Documented causes: Low battery.. See the table for the matching fixes.
Documented causes: Fuel below generator pickup level in tank.. See the table for the matching fixes.