Low Oil Pressure Fault (2 Blinks)
The ONAN-2 (Cummins Onan) diesel fault code means: Low Oil Pressure Fault (2 Blinks). This is a critical severity code.
- Keep running?
- No — shut it down
- DIY difficulty
- easy
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-2?
- The generator shuts down, or will not keep running
- The status light on the Start/Stop switch blinks twice, pauses, and repeats
What Causes ONAN-2? (Most Likely First)
- Low engine oil pressure: Cummins defines two blinks as a low oil pressure fault Very Likely
- Low oil level; Cummins tells RV owners to check the oil level every 20 hours of running Likely
- A faulty oil pressure sensing switch or its wiring Possible
Can I Keep Running It with ONAN-2?
No — shut it down. ONAN-2 is rated critical 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-2 on specific platforms — tap a platform for the fix and the exact part:
Onan QG 4000/5500/7000 (gasoline RV gensets) Easy DIY
Onan blink-2 (Low Oil Pressure) on RV gensets is most often a low oil level rather than a pump or switch failure. RV gensets sit at angle when the rig is off-level and can shutdown long before the dipstick reads low. First check oil level on level ground. If level is correct, the pressure switch ($30-$50) on the side of the block is the next suspect -- they fail closed (always-on signal) more than open. Verify with a mechanical gauge before condemning the pump.
Labor: 20-40 minFrequently Asked Questions
What does two blinks mean on an Onan RV generator?
Cummins defines two blinks as a low oil pressure fault. It is not the overheating code: that is one blink.
How often should I check the oil?
Cummins' RV Generator Handbook says to check the oil level every 20 hours of running.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose ONAN-2?
Do not keep restarting the generator: running an engine without oil pressure damages it.
With the generator off and level, check the oil level and top up with the oil type in your operator's manual.
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 the oil level is correct and it still shuts down on two blinks, have a Cummins Onan dealer or service center check it.
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
Which Vehicles Commonly Get ONAN-2?
- 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.