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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14411
Experience:  Certified on Onan and Generac generators
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Im trouble shooting my Onan 5500 HGJAB Spec B. The engine

Resolved Question:

I'm trouble shooting my Onan 5500 HGJAB Spec B. The engine runs as long as I engage the start button. When I release it the genset shuts down. Using the owner’s manual I ran a diagnostic and got a fault code 36. I'm getting good fuel flow thru the low pressure pump, I changed the fuel filters, I thought it could be a clogged carb jet so I purchased a new carb and replaced the old, changed the oil and filter, blew the fuel pick up line out and pressurized the main fuel tank and got good fuel flow, changed air filter. The new carb electric choke is operating, fuel sensor is ok, and exhaust is ok. When those things didn't solve my problem I purchased a Service Manual from Onan got my multi-meter out. In addition to the above test I check spark plugs, ok, governor, actuator, linkage and spring, ok, spark plug and cables, ok, kill leads harness connector, ok.
I tested the magnetos for continuity. I got continuity on P1-15 and NO continuity on P1-20. I also check T1 and T2 for AC voltage output. I got 29 VAC on T1 and none on T2. I didn't check T3 or T4. The brushes are ok and I was able to visually look at the slip rings and they seem to be okay. I haven't checked input or out puts from the PC control but all fuses and breakers are good and working properly.
My wife said that when the genset shut down it made a rattling sound and sound similar to a fan belt squealing, like you would hear from a slipping fan belt on an auto engine. According to the service manual the generator has a belt drive, but I don't know how the check the belt without pulling the generator out of the couch (which is a 2003 Bounder 36' Class A).
I ran another self diagnostic using the service manual and I no longer get a Fault 36 but I am getting a Fault 4. The service manual requests a measurement of the field; quadrature and main winding resistance but I don't know how to do that unless it has to be done by removing the genset from the coach.
Do I need to replace ignition module 2 since I'm not get continuity?
Should I also replace ignition module 1 if I replace module 2?
Can they be replaced without taking the genset out of the coach?
Is possible it's the VR or a PC control board problem?
Do I have to pull the genset out to check the drive belt (I didn't know the generators are belt driven)?
How do I check the quadrature and main winding resistance without taking the genset out of the coach and how is that test performed?
Any other suggestions or advise would sure help and be appreciated. Thanks San Antonio, FL
Submitted: 6 years ago.
Category: Small Engine
Expert:  Hank F. replied 6 years ago.


If you are getting no continuity from P1-20 to ground, either that wire is broken or the magneto is bad.


To check the belt drive, the genset must be removed from the coach to be able to remove the base cover. There is no way around it. The magneto is mounted under the flywheel, so it must also come out to replace the magneto.


You can test the windings without removing the set. To test the resistance of the field (rotor), look at the generator above the controller. You will see a small plastic 'plug' with one 10mm bolt and 2 wires. This is your brush holder. Simply remove the two wires, and ohm across the terminals the wires were attached to.

To test the main windings, remove the controller cover, disconnect the controller P1 plug, disconnect T1 and T3 from the circuit breaker, and T2 and T4 from the grounding post.


Main winding 1 is T1 to T2.

Main winding 2 is T3 to T4.

Quadrature winding is P1-3 to P1-9.


All of them should fall within the specifications in your manual, none should have continuity to each other or to ground.

Hank F., Technician
Category: Small Engine
Satisfied Customers: 14411
Experience: Certified on Onan and Generac generators
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