Went to fire up my Onan 4000 generator for the 1st time this year. Held the Start/Prime switch down on Prime and the light came on and flashed like usual. After about 5 seconds I released the switch as usual and pushed the Start side of the switch. Nothing happened - - totally dead. Tried the Prime side of switch again - - nothing happened. Last time this happened (generator dead) 7 years ago the cause was a faulty circuit board that needed to be replaced.Anything else I should be checking before I order a new circuit board?

I had the same problem with my onan 6500. I cleaned the battery cable connection at the battery and all was good. What threw me off is all the coach lights worked but the gen was dead.

Do you have 12VDC at the generator?

Apparently I do have 12 VDC at the generator because the light came on when I 1st went to Prime the generator. But I will definitely check to make sure that there is 12VDC at the generator before I order a new circuit board. I just reconnected all the battery cables to the coach batteries before attempting to start the generator so the connections are all clean.

DouglasC wrote:Apparently I do have 12 VDC at the generator because the light came on when I 1st went to Prime the generator. But I will definitely check to make sure that there is 12VDC at the generator before I order a new circuit board. I just reconnected all the battery cables to the coach batteries before attempting to start the generator so the connections are all clean.The light may come on even if there is 10 or 11 volts. It will not turn over unless it sees a certain voltage or greater. Don’t assume by the light coming on . Measure it at terminals where it goes into generator. There is also a relay under the enclosure that is a start relay that goes bad. They can be purchased at an auto parts store. How do i know... been there done that

Yes, clean. Use a battery cleaning agent (do internet search for how to clean) on terminals and any electrical connection. It is amazing how two metals can touch, look clean, yet not conduct electricity. Start here, this is free.

Dead Onan 4000 generator | Good Sam Community

madjack60
Explorer
Mar 21, 2021
I had the same problem with my onan 6500. I cleaned the battery cable connection at the battery and all was good. What threw me off is all the coach lights worked but the gen was dead.
Old-Biscuit
Explorer III
Mar 21, 2021
Do you have 12VDC at the generator?
DouglasC
Explorer
Mar 21, 2021
Apparently I do have 12 VDC at the generator because the light came on when I 1st went to Prime the generator. But I will definitely check to make sure that there is 12VDC at the generator before I order a new circuit board.

I just reconnected all the battery cables to the coach batteries before attempting to start the generator so the connections are all clean.
Ranger_Smith
Explorer
Mar 21, 2021
DouglasC wrote:
Apparently I do have 12 VDC at the generator because the light came on when I 1st went to Prime the generator. But I will definitely check to make sure that there is 12VDC at the generator before I order a new circuit board.

I just reconnected all the battery cables to the coach batteries before attempting to start the generator so the connections are all clean.

The light may come on even if there is 10 or 11 volts. It will not turn over unless it sees a certain voltage or greater. Don’t assume by the light coming on . Measure it at terminals where it goes into generator. There is also a relay under the enclosure that is a start relay that goes bad. They can be purchased at an auto parts store. How do i know... been there done that
ajriding
Explorer II
Mar 22, 2021
Yes, clean. Use a battery cleaning agent (do internet search for how to clean) on terminals and any electrical connection. It is amazing how two metals can touch, look clean, yet not conduct electricity. Start here, this is free.
bukhrn
Explorer III
Mar 22, 2021
I assume you are trying the remote switch in the house, have you tried the switch on the generator it's self?
DouglasC
Explorer
Mar 22, 2021
bukhrn wrote:
I assume you are trying the remote switch in the house, have you tried the switch on the generator it's self?

Yes, I have been tried the switch on the generator after the remote switch failed to work in starting it. No luck there either.
DouglasC
Explorer
Mar 22, 2021
Ranger Smith wrote:
DouglasC wrote:
Apparently I do have 12 VDC at the generator because the light came on when I 1st went to Prime the generator. But I will definitely check to make sure that there is 12VDC at the generator before I order a new circuit board.

I just reconnected all the battery cables to the coach batteries before attempting to start the generator so the connections are all clean.

The light may come on even if there is 10 or 11 volts. It will not turn over unless it sees a certain voltage or greater. Don’t assume by the light coming on . Measure it at terminals where it goes into generator. There is also a relay under the enclosure that is a start relay that goes bad. They can be purchased at an auto parts store. How do i know... been there done that

OK - - I tested the voltage coming into the generator - - 12.9 VDC. If the problem was only a bad starter relay, why wouldn't the primer still work? I'm still leaning toward a bad circuit board since nothing works - - the generator appears to be dead!
DrewE
Explorer II
Mar 22, 2021
Have you checked the 12V fuse on the generator? It's an easy, low-hanging fruit sort of check. Checking that all the connectors in the guts of the generator (through the firewall) are clean and tight is also worth checking/trying.
Ranger_Smith
Explorer
Mar 22, 2021
Mine would prime then nothing. There are 3 separate relays in there. Search the internet for your model of generator and you will find a maintainence and troubleshooting manual.

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