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Old 09-04-2014, 03:10 PM   #1
Join Date: May 2014
Posts: 30
Onan Generator Problem - code 37

Hi folks!
I have a 2011 Thor Hurricane Class A gas Motorhome with an Onan 5500 generator and 2 A/C units. The generator cranks and runs fine with the a/c units going for a few hours, but then would trip the 20 amp a/c breaker located on the side of the generator. After asking around, everyone said that it was probably a bad breaker. So, I ordered the new breaker and replaced it. Now the generator will run with the a/c units going for anywhere from 2 to 13 hours and then the generator will die (not trip the a/c breaker). The generator will not restart until it cools down a few hours. It will then start and repeats the whole process again.

(Point of note - the a/c units work fine when they are plugged up.)

Frustrated....I brought it to an Onan certified shop because I really need it fixed quickly for some upcoming tailgating events. (It will need to run from Friday thru Sunday for tailgating.)

The shop said it shows a fault code 37. When I asked what that means, I was told that it has something to do with the ignition or coil, but they said they need the generator to die while it is in the shop so they can narrow down the problem instead of just replacing parts that may or may not be the problem. Naturally as you may have that it is in the shop, the generator will not die. It has been there for 2 days.

I feel sure that unless it dies and the shop can find the real problem, I will get it out tailgating and she will bite the dust and leave me sweating in the 90 degree Louisiana heat.

Anybody have any suggestions for a code 37?
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Old 09-04-2014, 07:29 PM   #2
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Thor Owners Club
Freightliner Owners Club
Join Date: Sep 2013
Location: Youngsville, LA
Posts: 573
What shop did you bring it to?? if you are in lot 407 and it dies come find us.. we'll be soaking up some a/c and icy beverages..
Billy and Danielle
2013 Thor Palazzo 33.3
2019 Jeep Wrangler Unlimited Rubicon
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Old 09-05-2014, 05:45 AM   #3
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Join Date: Nov 2009
Posts: 2,043
I'll assume it's an HGJAB model generator.

An error 37 can be tricky, and it sounds as if the shop you have it at knows this. There are a wide range of items that can trigger this error, but in many cases I've repaired it's the drive belt slipping due to a seized tensioner pulley.

The only definitive way to find exactly what's wrong is for the service center to hookup a load bank to your generator while it's in the coach and tell-tale voltmeters on a break-out box. As it's running it's imperative to see the timing of events as the issue begins to occur. The load bank will allow them to bring the amp draw on the generator right up to it's limits - which will quickly show a slipping belt by the indicating a decline in HERTZ.

While on the load bank, running at max amperage, this will also cause the unit to build heat and become heat soaked quickly - no need to run for 12 hours! Once all the electronic components (control board, rotor, stator) are heat soaked if they are bad, they will fail quickly with the expansion/contraction from the heat.

Once the units fails and sets the 37 error it's imperative that they quickly do the ohm measurements on the rotor, stator and quad windings while it's still hot.

In some cases the 37 can be caused by a failing ignition magneto which causes the unit's ignition timing to become either retarded or advanced. BUT you would most likely hear the generator sputter, cough, perhaps even backfire a few times before it shuts itself down, so if you're not experiencing any of that then I would start troubleshooting elsewhere.

If all else checks ok then it's entirely possible the control board is at fault, but I've never replaced one on this error code.... From my experience it's always been the drive belt system....

Unfortunately, unless it is the control board, the generator will have to be removed from the coach and disassebled to get to either the drive belt or the magnetos..
94-Newmar Kountry Star 40-KSDP
Spartan/Cummins 8.3C-300HP/Allison 3060 WTEC-II/25yr RV Tech RVIA Certified/Onan-Cummins Certified
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