RV OWNER’S FIELD GUIDE
Generator Troubleshooting
A generator that won’t start, won’t stay running, or won’t produce power is one of the most common calls we get — and one of the most preventable. Here’s how to think through it.
Won’t Start
Generators that sit unused for months develop fuel system problems — varnish buildup, stale fuel, and gummed jets are the top causes of a no-start. Work through these first:
1. Check fuel level and fuel shutoff valve position
2. Verify the generator’s own start battery has charge — a separate issue from your house battery
3. Check for fault codes on the control panel if equipped, and don’t just clear them — note what they say first
4. If it cranks but won’t fire, suspect stale fuel or a stuck choke — both common after winter storage
5. If it won’t crank at all, check the main breaker and any safety interlocks (compartment door switches on some models)
PRO TIP
Ethanol-blended fuel breaks down faster than people expect. If your generator sits more than 30 days between uses, run it dry or add a fuel stabilizer before storage — it’s the single biggest thing you can do to prevent a no-start next time.
Starts But Won’t Stay Running
A generator that fires and then dies within seconds is telling you something specific — it’s rarely random.
— Low oil shutdown — many units won’t stay running if the oil level sensor trips, even if oil looks fine visually
— Fuel starvation after the initial fuel in the carburetor bowl burns off — points to a clogged fuel filter or fuel pump issue
— Carburetor gummed from old fuel — the engine runs on residual fuel then stalls
— A failing ignition module that works briefly under cranking RPM but drops out
Runs But Produces No Power (or Surges)
This is a generator head or governor problem, not a fuel problem — the engine side is fine, but the electrical output isn’t right.
— Surging or hunting RPM at idle or under load usually points to the governor or a fuel delivery inconsistency
— No output at all with the engine running normally suggests a failed AVR (automatic voltage regulator) or worn carbon brushes
— Shuts down specifically when a large load (AC unit) is applied — often an overload condition from low output voltage, not an actual overload
— Output voltage and frequency should be tested under actual load, not just at idle — a generator can look fine unloaded and fail the moment real current is drawn
⚠ Carbon Monoxide Warning
Generator exhaust contains carbon monoxide (CO), which you can’t see or smell and which can kill. Cummins Onan warns that walls, snow banks, high grass, brush and other vehicles can trap exhaust in and around the RV. Clear snow away from the tailpipe and the generator compartment before every start, and keep checking it while it runs.
Keep nearby windows, doors and roof vents closed on the exhaust side. Don’t run power vents or exhaust fans while parked with the generator running, because they can pull exhaust inside. Never run it with a damaged tailpipe or an exhaust leak.
Never sleep in or occupy the RV with the generator running unless it has a working, tested CO alarm. Test it before every trip and replace it by its expiration date. If anyone gets a headache, dizziness, nausea or drowsiness, get everyone into fresh air, shut the generator off and call 911.
Basic Maintenance That Prevents Most of This
— Exercise the generator at least 2 hours every month it’s not in regular use, at about half (50%+) of rated load. Cummins Onan says one 2-hour run beats several short ones
— Use a fuel stabilizer if the rig sits more than 30 days
— Change oil and filter per manufacturer interval — typically every 100–150 hours
— Keep the fuel tank at least half full to reduce condensation buildup
— Clean or replace the air filter regularly, especially in dusty conditions
When to Stop and Call a Professional
Both “starts but won’t stay running” and “runs but produces no power” are symptoms of specific, diagnosable problems — they get worse with continued operation, not better. If you’ve checked fuel, oil, and the basics and it’s still not right, stop cranking on it. Fault code reading, output testing under load, and carburetor service are all things worth having done properly rather than guessed at.
OUR TOOL KIT
Generator service parts
Cummins Onan 122-0645 oil filter — The OEM oil filter for most Onan RV gensets.
Cummins Onan 140-3280 air filter — The OEM air filter for Onan MicroQuiet 4000.
Klein RT250 GFCI outlet tester — Finds open grounds and reversed polarity in seconds at every outlet.
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