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Old 02-16-2017, 08:06 PM   #1
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Brand: Thor Motor Coach
Model: Challenger 37TB
State: Kentucky
Posts: 1,027
THOR #1020
Onan Marquis 5.5 Generator Brush Replacement

First off a little background:

We dry camp for 2-3 months each winter in Florida and use our generator a lot. I routinely change the gennie oil, oil filter and air filter every 150 hours. Additionally, I change the plugs every 500 hours. (Note: if you haven't done a plug change, the first time is a real learning experience - take a look at http://www.thorforums.com/forums/f8/...00-a-5424.html for some help).

I also routinely use Sea Foam to keep the carburetor cleaned up.

This year I had a whole new problem.

1. Gennie would start and run for about 10 seconds then cut off. The 10 seconds is just about when the generator starts producing 110v.

2. Generator code (blinking lights) is 3 - 3. Then while in diagnostic mode shows a 15. Get the Onan manual and it has a section on these codes and diagnostic mode.

3. Leaving the gennie in diagnostic mode, restart the gennie without priming. Generator will again cut off and give you a 3 - 3 code. Go back into the diagnostic mode, cut off the circuit breakers on the generator and restart. If generator continues to run after 10 seconds, it is strictly an issue with the generator portion and not the gas engine portion.

Lots of post about gas, carburetor, etc. Nope if you follow the above fault logic, it is generator related. Most common root cause is the brush set.

Hats off to Cummins - they were great about servicing my gennie under warranty and pointed out the location of the problem.

Below is a pic of the location and cover of the brush set.

Also, found a video on brushes for a Onan 7000. One of the reason I didn't post more explicit information, this video is very useful. While the brushes for the Onan in the video are on the right hand side, the brushes for the Onan 5500 are on the left hand side. Thus the reason for posting the pic.

Here is a link to the video on brush replacement. https://youtu.be/kUvzwKJYB-g

PS: about a $60 part.
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