RV generator won’t start: cranks, clicks or does nothing

Common symptoms

• You press START and nothing happens: no crank, and the light on the switch stays dark.
• The generator just clicks, or the starter kicks in and drops out.
• It cranks slowly, like the battery is tired.
• It cranks strongly for about 30 seconds, stops, and the light blinks 4 times.
• It won’t start after sitting for a few months, or it starts and runs rough.
• It fires, runs a few seconds, then dies.

Quick checks before anything else

• The RV has fresh fuel well above the point where the generator last quit. Fill up if in doubt.
• You held the switch at STOP/PRIME for 30 seconds before cranking.
• The oil sits between the marks on the dipstick, checked on level ground.
• The battery cables are clean and tight at the battery and at the generator.
• The air conditioner and other big loads are off.
• You counted the blinks on the status light after the last failed try.
• No fuel smell and no wet spots under the generator.

Why won’t my RV generator start?

• Fuel below the generator pickup The gauge shows fuel, but the generator’s pickup tube sits higher in the shared tank, so it cranks and won’t fire.
• Empty fuel lines After running dry, a filter change or a long sit, the lines need priming before the engine can catch.
• Weak starting battery or loose cables No status light, a slow crank, or a starter that clicks in and out.
• Stale fuel Gas left without stabilizer forms gum and varnish that cause hard starting and rough running.
• Spark plug, air filter or thick oil A loose plug wire, worn plug, dirty filter or too-thick oil can all end in an over crank fault. On LP models, so can a low tank on a cold day.

Step-by-step: getting an Onan generator to start

If your RV generator won’t start, go in this order; the first steps cost nothing. Note what the status light does on each try, because it tells you which step you need.

1. Read the status light first A dark light when you press START points to battery power (step 4). Flashing while it cranks, then 4 blinks, is an over crank fault: it cranked the full time and never started, which points to fuel (steps 2 and 3). Three blinks means a stored service code: press STOP/PRIME once and count the two-digit code, then look it up in our Onan QG 4000 code list. Code 32 means it cranked too slowly, which is the battery again.
2. Fill the tank, then think about the pickup When the generator and the engine share a tank, Cummins says the pickups are usually set so the generator runs out first. Cummins’ inverter manual says most RVs cut off generator fuel well before the gauge reads empty. Fill up first, and mark the gauge where yours quits.
3. Prime for 30 seconds Hold the switch at STOP/PRIME for 30 seconds. The status light stays on while the fuel pump runs. Cummins says to prime after running out of fuel or changing the fuel filter, and the QG 2800i manual adds any time it has not run within 8 hours. Don’t hold it for minutes: on several models, priming longer than 3 minutes sets code 57.
4. Check the starting battery The generator’s control and starter run on a 12 volt battery. Clean and tighten both cables at the battery and at the generator, since loose or corroded connections make starting harder. Then charge the battery. A fully charged lead-acid battery reads about 12.6 volts at rest. Cummins sets a minimum battery size in cold cranking amps (CCA, how much current a battery can deliver in the cold): 450 CCA at 0°F for the QG 4000, QG 5500 and QG 7000, and 650 CCA for the QG 2800i. Check the label on yours.

   

5. If it just clicks, look at voltage under load A starter that engages and then drops out means cranking voltage is dipping below 6 volts, Cummins says. Its fixes, in order: run the motorhome’s engine while you try to start the generator so the engine’s alternator holds the voltage up, then clean, tighten and charge the battery, then fit bigger battery cables or run parallel ones. On the QG 4000, a status light that goes out while cranking can mean an internal short tripped a self-resetting protection device. Try once more. If it happens again, call a dealer.
6. Try the other switch Many RVs have a remote start switch inside and a second switch on the generator. If one does nothing, Cummins says to try the other.
7. Check the oil Park level and stop the generator. Pull the dipstick, wipe it, put it back in without screwing it down, then pull it again and read it. Keep the level between the marks. Cummins warns too little oil can cause severe engine damage, and models with an oil switch will shut down on it (code 2, or code 6 on inverter models). Oil that is too thick for the weather slows cranking. For cold weather, Cummins lists 5W-30 for about -20 to 50°F.

   

8. Clean up the ignition and air side Cummins’ over crank list goes on after fuel: push the spark plug wire on firmly, replace the spark plug, replace the air filter if it is dirty, tighten any leaking fuel fitting and prime again, and replace the fuel filter. On LP models, check the propane tank. On cold days Cummins says it may need to stay at least half full to make enough vapor.
9. Deal with stale fuel after storage If the generator sat for months with no stabilizer, Cummins warns the gas breaks down into gum and varnish that cause hard starting and rough running. Fill up with fresh gas, prime, and try again. If it still won’t start, or starts and runs rough for a long time, the fuel system likely needs cleaning by a dealer. If the engine was fogged for storage, Cummins says the fogger may have fouled the spark plug, so clean or replace it.
10. Respect the starter rest time After an over crank, wait 5 seconds for the control to reset. After 5 tries, let the starter cool for 30 seconds. Cummins warns the starter motor can be damaged by overheating.

Gas, diesel and inverter Onan models

QG gasoline (2800, 4000, 5500, 7000). These crank for about 30 seconds before an over crank fault. The QG 4000 has no low oil code in its fault list. The QG 2800, 5500 and 7000 shut down on low oil pressure with 2 blinks.

QD diesel (6000, 7500, 8000). The status light flashes during preheat as well as cranking. Cummins adds air in the fuel line from a loose fitting to the over crank causes. Its battery minimum is 450 CCA down to 0°F and 650 CCA down to -20°F.

Inverter models (QG 2800i, 4000i DF, 7000i DF). The 2800i manual’s advice for “cranks but does not start” is to let it crank until code 4 comes up. On the 4000i and 7000i DF, over crank comes after 15 seconds, and the 7000i manual says to hold START for more than 3 seconds, then release and wait. Code meanings differ from the older QG list, so read codes from the list for your exact model. If yours starts but quits a few minutes later, see Onan generator keeps shutting off.

Once it starts and runs, an RV with dead outlets is a different problem: see RV generator running but no power. Our RV generator repair guide lists the specs for each model.

When to call an RV tech

• Any fuel or exhaust leak, or a fuel smell you can’t trace.
• The status light goes out during cranking a second time.
• Fresh fuel, a full prime, a good battery and a new plug, and still no start.
• It shows a code the manual has no owner fix for, such as 12, 14, 35 or most codes in the 40s.
• The fuel system needs cleaning after storage.
• The starting battery keeps running down. Cummins says to install or service a charging system in the vehicle, and our battery not charging guide covers the house side.

Common questions