GENERATOR DEEP DIVE
Onan, Cummins & Honda Generator Troubleshooting & Service Guide
Manufacturer-specific fault codes, no-start diagnostics, and service intervals for the generators most RVers actually own — built-in Cummins Onan gensets and portable Honda inverter generators.
Onan & Cummins Built-In Gensets: No-Start Diagnostics
WORK THROUGH THIS BEFORE ASSUMING THE GENSET IS DEAD
Most “dead” Onan/Cummins RV generators aren’t actually dead — they’re starved of fuel, low on oil, or sitting on a weak start battery after months of storage. Check these in order:
1. Fuel level above 1/4 tank — many gas-genset no-starts on a “full” RV are really a fuel pickup tube that sits above the actual fuel line
2. Engine oil level — low oil trips a safety cutoff and will prevent the unit from cranking or running at all
3. Start battery voltage — slow cranking or no cranking after storage is almost always a weak or disconnected battery
4. Old or contaminated fuel — gas that’s sat unused for months gums up the carburetor and fuel filter
5. Automatic transfer switch and control board connections — a loose harness connector reads as “no start” even with a healthy engine
PRO TIP
If your genset sits unused for more than a month at a time, that’s exactly the condition that breeds fuel-gumming and battery drain problems. Exercise it at least 2 hours every month at about half (50%+) of rated load. Cummins Onan says one 2-hour run beats several short ones. Use a fuel stabilizer if it’s going to sit longer than 30 days.
⚠ 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.
Onan Fault Code Reference & How to Read Them
DECODING THE FLASHING LED
Most Onan/Cummins RV generator control panels report faults through a flashing LED rather than a text screen. After a fault shutdown, the status light blinks the code on its own: 3 blinks means a service fault, and 4 blinks means overcrank. Press Stop once to show the two-digit code, which is the tens digit, a short pause, then the ones digit. For example, blink-blink, pause, then seven blinks is Code 27. The code stops blinking after about five minutes. Press Stop three times within five seconds to bring it back (some diesel models say three seconds). The last fault logged keeps showing even after the cause is fixed.
Code 2 / 23 Low oil pressure — check oil level first, then the sending unit
Code 3 Service check — general fault, check other stored codes
Code 4 Over crank — engine cranked without starting, usually fuel or ignition
Code 12 / 13 Over/under voltage output
Code 14 / 15 Over/under frequency — often an engine speed or governor issue
Code 19 Governor actuator fault — controller senses an open or shorted actuator circuit
Code 22 Governor actuator overload — running at or near full-duty cycle too long
Code 27 Voltage sense error
Code 29 High battery voltage — check the charging system/converter
Code 31 Overspeed
Code 32 Low cranking speed — weak start battery or bad connection
Code 35 Control card failure
Code 36 Engine stopped — can range from empty fuel tank to a serious mechanical fault
Codes are a starting point, not a diagnosis. The same code can point to three or four different root causes depending on your model — if you’re not comfortable chasing it further, that’s exactly what a diagnostic call is for.
Onan/Cummins Service Intervals
MISSED SERVICE IS THE #1 CAUSE OF GENSET FAILURES WE SEE
Break-in oil change 50 hours on a brand-new unit, to clear break-in contaminants
Oil & filter (gas models) Every 100–150 hours, or annually, whichever comes first
Oil & filter (diesel models) Every 250 hours or one year
Spark plug (gas models) Every 450 hours to keep clean, reliable ignition
Air filter Inspect every 50 hours, replace at 500 hours or annually — sooner in dusty conditions
Fuel filter Every 500 hours or two years
Spark arrestor Clean once a season
Exact intervals vary by model — these are the general Onan/Cummins RV genset ranges. If you don’t know your engine hours or last service date, that’s worth figuring out before your next long trip, not after a failure at the campsite.
Honda Portable Generators (EU2200i / EU3000iS)
THE MOST COMMON PORTABLE FOR BOONDOCKERS & TOWABLE OWNERS
The three most common reasons a Honda portable won’t start are stale fuel (gas can start breaking down in as little as 30 days), a carburetor gummed up from that stale fuel, and a fouled spark plug. All three are DIY-fixable, and all three are prevented by simply not letting the unit sit full of gas for months at a time.
Oil type 10W-30 in both the EU2200i and EU3000iS
First oil change 20 hours (break-in)
EU2200i oil change interval Every 100 hours, or every 6 months, whichever comes first
EU3000iS oil change interval Every 100 hours, or every 6 months, whichever comes first
Air filter Foam element — wash in warm soapy water, dry, and lightly oil before reinstalling
Oil drain EU2200i: no drain plug. Oil drains only through the filler neck, so remove the maintenance panel first. EU3000iS: has an oil drain bolt, so drain it there per the owner’s manual
PRO TIP
Don’t let a portable generator sit for a full season with fuel in the tank and carburetor. Either run it dry before storage or use a stabilizer — a gummed carburetor is the single most common reason we see a “dead” Honda that’s actually a $20 fix.
OUR GENERATOR PICKS
Generators & genset service parts
Quiet 2,200W inverter generator; the common pick for trailers and vans
2,200W inverter with fuel gauge and CO shutoff
Gas or propane, with a TT-30 RV outlet built in
4,500W portable from the same maker as most built-in RV gensets
OEM air filter for Onan QG 4000-series gensets
OEM oil filter for Onan RV gensets
Cuts A/C startup surge so a smaller generator can run it
Want it installed? We do that. Request an Appointment · Remote consult · All our generator picks →
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Stuck on a Fault Code, or Want Us to Just Handle It?
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