Overcrank: Cranked Over 30 Seconds Without Starting (4 Blinks)
The ONAN-4 (Cummins Onan) diesel fault code means: Overcrank: Cranked Over 30 Seconds Without Starting (4 Blinks). This is a serious severity code.
- Keep running?
- No — shut it down
- DIY difficulty
- moderate
A $30 car code reader can't do diesel. The HD7000 reads full-system codes and does parked DPF regen, idle/speed-limit, and service resets from the cab — on everything from a 6.7 Cummins/Power Stroke/Duramax pickup to Class-8 trucks (Detroit, Paccar, CAT, Volvo, Mack, International).
Full-system 6/9/16-pin diesel scan tool for Cummins, Paccar, CAT, Detroit and more — plug-and-play, no subscription. A cheaper way to read heavy-duty codes a basic OBD2 scanner skips entirely.
Affiliate links — we earn a commission at no extra cost to you.
What Are the Symptoms of ONAN-4?
- The generator cranks but never starts, then stops cranking
- The status light blinks four times, pauses, and repeats
What Causes ONAN-4? (Most Likely First)
- The engine did not start: Cummins defines four blinks as cranking that exceeded 30 seconds without the engine starting Very Likely
- No fuel reaching the engine (empty supply, closed valve, clogged filter or hose) Likely
Can I Keep Running It with ONAN-4?
No — shut it down. ONAN-4 is rated serious severity. Continuing to run the unit in this state risks further damage — get it looked at before putting it back in service.
Common Fixes by Vehicle
What techs usually find when diagnosing ONAN-4 on specific platforms — tap a platform for the fix and the exact part:
Onan QG / RV gensets (gasoline) Easy DIY
Onan blink-4 (Overcrank) on RV gensets after sitting all winter is almost always stale fuel. Drain and refill with fresh fuel, replace the fuel filter ($15-$25), and consider adding stabilizer for next storage. If the fuel is fresh, suspect the fuel pump (electric, mounted near the tank, $60-$120) -- they fail with age. As a last resort, pull a plug and check for spark.
Labor: 30-90 minFrequently Asked Questions
How long does an Onan RV generator crank before code 4?
Cummins' handbook says four blinks means cranking exceeded 30 seconds without the engine starting.
Is four blinks the same as code 44?
No. Cummins notes that 44 has not been assigned as a fault code; four blinks on its own is the first-level overcrank code.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose ONAN-4?
Check that the generator has fuel: on many RVs it draws from the vehicle's own tank or LP supply.
Check the fuel filter and hoses for blockage or leaks.
The code stops blinking after five minutes (15 minutes on Series HGJAA). To see it again, press Stop three times within five seconds; the last logged fault blinks even if the condition has cleared.
If it still will not start, have a Cummins Onan dealer or service center check it rather than cranking repeatedly.
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
Which Vehicles Commonly Get ONAN-4?
- Cummins Onan RV generators with a status light on the Start/Stop switch (gasoline, LP and diesel models)
- Not the RV QD 3200, which shows text messages on its display panel
Explore More
Was this helpful?
Send this to whoever is fixing the truck — your tech, or the person asking what the fault means.