High Engine Temperature Shutdown Triggered
The ONAN-2 (Cummins Onan) diesel fault code means: High Engine Temperature Shutdown Triggered. This is a critical severity code.
- Keep driving?
- No -- stop driving
- DIY difficulty
- easy
- Estimated cost
- DIY: $0-$80 (cleaning vents, replacing air filter, topping coolant or oil). Professional sensor or cooling system repair: $150-$600 depending on model and labor rates.
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).
Check Price on AmazonAffiliate link -- we earn a commission at no extra cost to you.
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.
Check Price on AmazonAffiliate link -- we earn a commission at no extra cost to you.
Common Symptoms
- Generator shuts down suddenly during use and will not restart
- Control panel LED flashes exactly 2 times repeatedly after shutdown
- Engine feels extremely hot to the touch near the exhaust or shroud
- Generator ran fine for a while then shut off without warning
- Air coming from the genset compartment vent is unusually hot
- Generator may restart briefly but shuts down again within minutes
- Burning or hot-plastic smell near the generator compartment
Probable Causes (Ranked by Likelihood)
- Blocked or restricted compartment ventilation, debris or insulation covering the intake or exhaust vents Very Likely
- Low coolant level or coolant leak on liquid-cooled models (QD series) Very Likely
- Failed or seized cooling fan or fan belt on the generator itself Likely
- Overloaded generator running at or above rated wattage for extended time in hot ambient conditions Likely
- Faulty engine temperature sensor sending a false high-temp signal to the controller Possible
- Clogged air filter restricting airflow to the engine on air-cooled models Possible
- Low oil level causing increased internal friction and heat buildup Less Likely
Step-by-Step Diagnostic Procedure
Let the generator cool completely, at least 30 minutes, before touching any components. A hot shutdown means surfaces may be hot enough to cause burns.
Check all compartment vents on the exterior of the RV or vehicle. Remove any debris, leaves, mud-dauber nests, or objects blocking the intake and exhaust openings. This is the single most common cause of Code 2 on RV gensets.
On air-cooled models (QG 4000, QG 5500, Microlite, MicroQuiet), remove the generator access panel and inspect the cooling shroud and fan. Spin the fan by hand. It should rotate freely with no grinding. Look for broken fan blades.
Check the engine oil level using the dipstick. Oil should be between the MIN and MAX marks. Low oil causes heat. If it is low, top it off with the correct viscosity before restarting.
On liquid-cooled models (QD 6000, QD 8000, QD 10000), check the coolant reservoir and radiator level when the engine is cold. A low coolant level on any QD series unit will trigger Code 2 very quickly under load.
Inspect the air filter element. A heavily clogged filter starves the engine of combustion air, which raises operating temperature. Replace the filter if it is gray, oily, or visibly clogged.
After clearing any obvious blockage and confirming fluid levels, restart the generator with a light load (no AC, no electric water heater). If it runs cool for 15+ minutes and Code 2 does not return, the root cause was likely airflow or overload.
If the generator still shuts down on Code 2 after all the above checks, the temperature sensor itself may be faulty. Testing the sensor requires an ohmmeter and the specific resistance-versus-temperature chart from the Onan service manual for your model. At that point, contact a Cummins Onan authorized service dealer.
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 / Microquiet RV gensets Easy DIY
Onan blink-2 (High Engine Temperature) on RV gensets is nearly always blocked compartment airflow. Check the genset compartment intake and exhaust louvers for blockage (mud daubers, debris, even storage items packed against the vent). Clean the cooling fins on the engine itself with compressed air. If it still trips after cleanup, the temperature switch ($25-$60) on the cylinder head is the next part. On Quiet Diesel models (Kubota-powered) check coolant level and the radiator fan belt.
Labor: 30-60 minFrequently Asked Questions
What does Onan Code 2 mean on my RV generator?
Code 2 means the engine got too hot and the controller shut it down to prevent serious engine damage. The controller detected that the engine temperature exceeded its safe limit, so it killed the engine. The LED on your control panel will flash 2 times, pause, and repeat until you clear it.
Can my generator still run with a Code 2 fault?
No. Code 2 is a hard shutdown. The generator will not produce power and will not stay running. It may crank and start briefly after it cools down, but it will shut off again quickly if you have not fixed the underlying cause.
How much does it cost to fix Onan Code 2?
If the cause is blocked vents or a dirty air filter, the fix costs nothing or just a few dollars for a new filter element. If you need a new temperature sensor, expect to pay $20-$60 for the part plus $100-$400 in labor at a shop. A cooling fan replacement on a QD series diesel can run $300-$600 total.
Will my generator start the next time the power goes out after a Code 2?
Possibly, but only if the engine has cooled down. Once it cools, many units will attempt to start again. However, if you have not fixed the cause, it will overheat and shut down again within minutes. Do not rely on this generator for emergency power until the Code 2 root cause is resolved.