Onan 5.5 EFI code 12 help

[Rich Biebel]

Remove the 1 10 mm bolt holding the black plastic cover/carrier that has the rocker switch and the breaker

Now you can clip a meter on the input side of the breaker but with it off.
Your just isolating the machine from anything downstream and trying to see what the voltage and frequency (HZ) is when it does run.

From all the things you said you did, I would plug in another known good control board to see if there is any change.

I fix them so I have lots of test boards.....

The high voltage fault code 12 says numerous things to check but most of them are not clear. Supposed to be 138 volts to trigger that fault code.

A Rotor or stator issue not out of the question...

Right now parts availability for many machines is very bad.

I just fixed a 5.5 with a seized upper rotor bearing and Onan does not sell those bearings separately....It is possible to replace them though and I did that repair a number of times.

Your machine should have ROM.....Run Only Mode.....allows you to run it even though it is not making AC output....

Starts, shuts down in a fault, you restart it within a minute and it will run with NO AC output and if it has a lighted rocker switch, it will be blinking rapidly telling you it's in Run Only Mode....

You can do things like artificially energize the field at the brushes with DC voltage to test the rotor and stators ability to produce AC voltage normally...

I use a variable power supply but a 12 volt battery will work....
Onan does list that procedure and what the AC output should be approximately.....with 12 volts in.......


A service manual would be real helpful and you can buy those online for maybe $20