The Onan QG 4000 is one of the most common built-in gasoline RV generators, but the exact spec letter still matters. Record the model/spec from the data tag before ordering parts or following a code chart.
If it will not crank
Check the battery source the RV uses for generator starting. Measure voltage while pressing START, not only at rest. Clean accessible battery terminals and grounds with power isolated. Check the generator fuse or breaker listed in the manual. Try the local start switch at the generator; if local works but remote does not, the remote panel or harness becomes suspect.
If it cranks but never fires
Confirm the motorhome fuel tank is above the generator pickup level. Many RV installations do not let the generator use the last portion of driving fuel. Prime exactly as the manual directs, then respect crank/rest limits. Check oil level on level ground, inspect the air inlet and exhaust outlet, and preserve any blink code before resetting.
If it catches then quits
Read Onan generator starts then dies. A short run can come from fuel starvation, low oil protection, overheating, control-board shutdown, carburetor trouble or load/output faults.
Do not do these things
- Do not spray starting fluid unless the generator manufacturer specifically allows it.
- Do not bypass low-oil, shutdown or start-control safeties.
- Do not keep cranking until the starter overheats.
- Do not adjust carburetor or governor settings to hide a no-start problem.
Related Onan pages
- Onan generator code 36
- Onan generator fuel pump symptoms
- Onan generator carburetor problems
- Onan fault-code guide
- RV generator won't start
Sources and review notes
Use the Onan QG 4000 operator manual matched to the model/spec on the data tag. Cummins lists QG 4000 manual families and model/spec guidance on its RV generator manuals page.
Use the generator decision tree
Choose no-crank, crank/no-start, shutdown or no-output and work from the safest checks first.
Diagnose generator problem