Community Forums

hypoxia · 06-12-2019, 05:48 AM

For the last year or two the Onan 12.5 HDKCB Spec B Intermittently shuts off with code 36. Sometimes it will restart immediately and sometimes it will start hours later but in the end it starts eventually - so far. I do not think it is a fuel issue as I have tested it and replaced the fuel pump and filter on principal, good flow and no air in the line that I saw.
Onan Service manual says after checking fuel, #7 is testing the 333-0707 Governor Actuator (haven't done that yet) and #8 is Replace the 300-5961 Control Board.

Anyone have experience with this problem?

I do have the current Manuals, Service, Parts, etc.

BigLar368 · 06-12-2019, 06:52 AM

Just curious what code 36 is?

WantAB · 06-12-2019, 06:59 AM

Below is a cut and paste from a Internet search...

"Fault #36 happens when the engine stops running due to a reason unseen by the controller /inverter unit.

The most common cause of this is running out of fuel , so you may want to replace the fuel filter as a first step.

The next thing I would do would be to run the genset with a shortest possible length of fuel hose drawing clean fuel from a fuel can. We need to try to isolate the problem from the coach. The fuel lines on the coach could be sucking air , or there could be a broken pickup tube inside the coach fuel tank.

The electric fuel pump could also be the problem. If the genset still quits running with the fuel container setup , I would suspect the electric fuel pump.

A defect in the controller/inverter could also cause this , but they are expensive to replace , and not the most likely."

hypoxia · 06-12-2019, 07:18 AM

Quote:

Originally Posted by BigLar368

Just curious what code 36 is?

"Genset Stopping Without Fault Condition - Code 36
(The Controller declared this fault because engine speed fell below 1000 RPM for 0.5 seconds, though not by controller action)"

znt1186 · 06-12-2019, 07:31 AM

Had a similar situation with my previous Allegro Bus. Tiffin installed an inline fuel filter on the coach that was not documented anywhere. Found it and removed it. Generator ran fine after that.

DegoRed · 06-12-2019, 07:50 AM

When I was younger and a lot dumber, I made the horrible mistake of buying a Thor MH, code 36 plagued me every single time I used the MH. Turned out my fuel was vaporizing in the fuel line due to heat. Thor had zero solutions to the problem. Thanks to this forum, about 10 of us who all had the same problem started trial & error solutions to solve the problem.

After a lot of work, we found a solution, adding a $25 in line fuel pump between the fuel tank and the generator to help push fuel to the generator. The basic issue was the fuel pump on the generator was sucking fuel from the fuel tank, but it really was not a strong pump, the heat generated running the generator and outside temp heat would vaporize the fuel in the line causing it to basically boil, the air bubbles would get into the line and the generator would stop.

Bottom line, after spending countless hours on phone with Onan, code 36 is 100% a fuel related problem. You either have a clogged fuel filter, your fuel pump is bad or going out, a crack in your fuel line, or your fuel is vaporizing due to heat. Trouble shoot your issue from fuel tank to engine and you will find your problem.

BigLar368 · 06-13-2019, 04:20 AM

Being that you have already changed out the pump and filter I would start looking at the pick up tube in the tank. It may have deteriorated or even broke off. Not sure about your RV but ours (2004 Camelot) has fairly easy access to the top of the tank. Would not take much time to look at that.

hypoxia · 07-02-2019, 07:04 PM

Update. I'm finally at a good place to work on the coach. I checked the fuel hoses which hold a vacuum and seem to be good but swapped the supply and return on principle. I also removed and checked the governor on the generator. It tests good electrically, mechanically and is smooth when pushed in by hand. I did not replace the fuel line from the inlet inside the generator to the fuel pump but did make a hose which can be installed quickly if the problem continues. I also have not removed the dip tube, it is extremely tight and I'm not willing to take the chance on breaking it off while on the road.

I should be dry camping this weekend to try it out.

NHRA225 · 07-02-2019, 07:28 PM

The Onan 12.5 HDKCB is notorious for for shutting down for no apparent reason except the control board and that's $800 from Onan and no guarantees it will fix the issue - From what I've been told from my local Onan guy is to wire up a separate switch to turn on the Fuel Pump off and on which bypasses the Board. Onan is aware of this issue and refuses to do a fix or recall.

hypoxia · 07-02-2019, 07:43 PM

Quote:

Originally Posted by NHRA225

The Onan 12.5 HDKCB is notorious for for shutting down for no apparent reason except the control board and that's $800 from Onan and no guarantees it will fix the issue - From what I've been told from my local Onan guy is to wire up a separate switch to turn on the Fuel Pump off and on which bypasses the Board. Onan is aware of this issue and refuses to do a fix or recall.

That is interesting and a switch would be an easy fix for normal operations. Is there a good way to power the fuel pump with an auto start when no one is home? I can see where a relay could be used to come on line after the start but not sure how to take it off line with the auto shutdown.

NHRA225 · 07-03-2019, 06:21 AM

Quote:

Originally Posted by hypoxia

That is interesting and a switch would be an easy fix for normal operations. Is there a good way to power the fuel pump with an auto start when no one is home? I can see where a relay could be used to come on line after the start but not sure how to take it off line with the auto shutdown.

Can't answer the Auto Start question. Friend of mine had the shut down issues with His, it would all of the sudden with a mild load seem like it ran out of fuel and shut off. after 2 trips to an out of town Onan shop with 2 -$800 boards replaced we visited our Onan shop here and reviewed the problem and that's when He was advised to wire an independent switch to control the Fuel pump. He hasn't had a Shutdown since. He wired a simple Lighted toggle switch with an inline 10 amp fuse directly to the fuel pump.

hypoxia · 08-11-2019, 05:58 AM

Quote:

Originally Posted by NHRA225

The Onan 12.5 HDKCB is notorious for for shutting down for no apparent reason except the control board and that's $800 from Onan and no guarantees it will fix the issue.

Winner winner chicken dinner!

I changed the control board and it appears to have fixed the problem.

Jamie65 · 08-12-2019, 05:08 AM

Some RV's have an external filter outside of the gen cabinet, on my Tiffin it was in the feed line where metal tube goes to hose a few feet from the gen, replaced the inline filter and problem went away. Any inline diesel filter will work.

hypoxia · 01-31-2020, 08:15 AM

Just an update. After changing the Onan Control Board the 12.5 generator has been running great for the last 6 months and 100 hours.

A side note; I was able to remove the generator governor with the top cover removed, no other disassembly required