Thursday, December 8, 2022


Troubleshooting Onan genset “won’t-starts”



By Chris Dougherty
Chris Dougherty is a certified RV technician. Here is a letter he received from a reader while he was serving as’s technical editor.

Dear Chris,
frustrated-womanI’m having a dilemma with my Onan generator. It won’t stay running and it quits when I take my finger off the START button, or cuts out and dies if it decides to run at all. It has been professionally tuned, has a new control panel, fuel pump is fine, etc., etc. No one can figure out the problem. HELP! It’s limiting the use of our RV. —Deb

Hi Deb,
It looks as though you’ve had this thing looked at professionally, but there are a couple of possibilities that are easy. First, how much fuel do you have in the coach? The generator uses a separate pick-up tube in the fuel tank which is higher than the engine tube. So, once your tank gets down to about 1/4, the genset will stop working so as not to use up all the fuel and stranding the coach. Second, make sure the oil is full. Onan gensets have a low oil cut-off that can affect the unit’s operation.

The newer Onan gensets will flash a code on the start switch light if they encounter a problem. If you go to they have a manual section which should give you additional troubleshooting options and a guide to deciphering the codes.

There are additional causes of these symptoms, which require specific testing of the system. I would recommend seeking out a Cummins Onan service center to have it looked at.


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Eldon Rhodes
6 years ago

I had the same experience with the Onan generator in my truck camper and will try to describe what I found to resolve the problem. I was trouble shooting the problem and saw an electrical spark (arc) as I was wiggling some wires while holding the start button on the generator. The insulation was worn through the black wire where a bundle of about 5 white wires and a single black wire run under the metal housing that the air filter mounts to. I stuck a piece of plastic between the wire and metal housing and problem solved. This is in an area that is not easy to see or to get to and I was lucky to see the spark. If not for that I probably would not have found it and I can understand that even an experienced technician could easily miss it.

Paul Lindstrom
6 years ago

The writer did not say if his onan has autogen start. I have had this problem that had me pulling my hair out (senior moments) until the the light bulb finally lit. Batteries were full and AGS was programmed to kick in at 12.2Volts. So therefore the the generator immediately shut down. Reprogramming the auto start solved the problem. An item easily overlooked even by the sharpest of technicians.