Onan RV Generator Turns Off Right After Starting [Fixed!]


We all expect our home away from home to provide us with reliable power for the necessities, but what do we need to do when our Onan RV generator won’t stay running after we’ve let our fingers off of the start switch?

This problem is most likely to occur in the spring when you go to start up your generator for the first time, or after a year or more of not using it.

As a general rule, an Onan RV generator will fail to stay running after the starter switch is released when the oil level is low or the oil pressure sensor switch is clogged or defective because it will not close oil pressure circuit. Filling with oil or replacing the switch will fix this problem and are simple procedures that can be performed at home with basic tools.

Don’t worry, if you’re not mechanically inclined, you’ll still be able to tackle this process and get your generator up and running for the summer season ahead!

Why an Onan RV Generator Won’t Stay Running After You Release the Start Switch

Generally, an Onan RV generator will turn off when you release the start switch if the oil level is low or if the oil pressure sensor switch is dirty or bad.

Luckily, this is a relatively easy fix even for someone who isn’t too mechanically inclined.

Before you do anything, check the oil level on your dipstick. If it is below the minimum level on the dipstick, or if you don’t see it touching the dipstick at all, then you will need to add oil (and change the oil, preferably if it’s been a while).

If your oil level is low, the solution is to simply make sure you add enough to raise the level to the appropriate marks on the dipstick.

If the oil level is fine, then we will need to proceed with checking the oil pressure sensor switch.

The oil filter and the wire leading to the oil pressure sensor switch are circled. The oil filter is below.

Before we get into this fix, we will want to confirm that a faulty oil pressure sensor switch is indeed the issue.

In order to test to see if the oil pressure sensor switch is the problem, do the following:

  • Remove the metal cover (with the “Onan” brand name on it) that is held on with 3-4 screws
  • Disconnect the single wire that leads to it
  • Ground that wire to the case or frame of the generator with either an alligator clip jumper or by pulling back the protective sheath on the wire-end and pressing it against the frame or case
  • With the wire grounded to the case or frame, start the generator

If the Onan RV generator stays running when this happens, then you know that the oil pressure sensor is your problem since you’ve closed the circuit that is required for operation by bypassing the switch.

image showing how to troubleshoot an Onan RV generator by grounding out the oil pressure sensor switch wire.
Grounding out the wire that was connected to the oil pressure sensor switch to the case of the generator to bypass the sensor and see if it was indeed the problem.

How to Repair or Replace the Oil Pressure Sensor on an Onan RV Generator

With the metal cover removed so that the oil filter and oil pressure sensor are exposed, go ahead and unscrew the oil pressure sensor from the generator.

The end of it will have a metal face at the end with a small hole in it.

You can attempt to salvage a dirty oil pressure sensor by spraying inside of that small hole with carburetor cleaner, CRC cleaner, or brake cleaner. Make sure to wear safety glasses to keep any from spraying back in your eyes.

Inside of the sensor is a diaphragm that can get gummed up with sludge and deposits from years of use and from sitting for a long time unused.

Do not poke around inside the hole with a wire, as you will puncture the diaphragm.

When working properly, the diaphragm will be pushed up into the sensor as oil pressures and cause a contact between the two points in the circuit and tell your generator that there is proper pressure.

That’s why shorting the sensor’s wire against the case or frame when testing for the problem will bypass this process by completing the circuit without needing the sensor to do its job. You’re essentially tricking your generator’s electrical system into thinking that the oil sensor is functioning and that the oil pressure is fine.

If, after having sprayed cleaner in the sensor a few times, the generator will still not stay running after the sensor has been reinserted, then you will need to replace it.

While you are at it, you had might as well replace the oil filter, change the oil, and replace the air filter if needed. This problem doesn’t take long to fix, but it offers the perfect excuse to do a few routine maintenance checks on your unit.

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Robert Van Nuck

Robert lives in central Michigan and enjoys running, woodworking, and fixing up small engines.

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