Onan 12.5kw issues

Ed McLawhorn Jr. · 10-14-2024, 10:19 PM

Need help on issues with 12.5kw diesel onan on my toterhome. Purchased toterhome in 2022 and no issues other than running rich (black smoke). Installed vent stack and gen would randomly cut off once or twice a weekend. No issues starting back and runing remainder of weekend. I didnt install stack and left storage door open for a couple races and no issues with cutting off. Recently, it has gotten worse and now cuts off 5-6 times during the weekend regardless of stack installed or storage door opened. This past weekend it was cutting off every couple hours. Most times, this weekend once it cut off, it would only start back after 20-30 minutes. Found code 45 and checked brushes today and they seemed clean. Only issue was one was much shorter than the other....seemed odd. Ordered new replacement brushes, but not confident brushes are the issue. Code 45 also indicates problem could also be pcb board. Assuming worst case, is it possible to change board without going to a onan repair dealer? Has anyone else had experience with code 45? Thanks for any suggestions.

Ed

Bill Grubbs · 10-15-2024, 04:52 AM

Filter change?
Air?
Fuel?
Type of diesel (B20/no1/no2)

Jack Zimmerman · 10-15-2024, 04:46 PM

I've been told that a pretty common failure issue on the Onan QD generators is the fuel pump power supply on the main circuit board. The symptom is that the generator will shut off randomly and it may or may not restart. Our 10K unit did it when it got hot and as far as I know, the only permanent fix is to get a new circuit board. However, an easy work around and a way to diagnose if that is the problem is to run a jumper wire from the + battery connection on the side of the generator to the fuel pump power wire which is accessible through a small cover on the front right side of the generator. If that fixes the problem you'll know it's the circuit board. And if you use that method to run the generator until you get a new circuit board (like I did), you just need to make sure you disconnect the jumper wire when you shut off the generator or the fuel pump will keep running.

Mike Pearson · 10-15-2024, 06:33 PM

Mine has an 8k QD Onan. One time it would not start. I took the front cover off and the spade connector for the fuel pump had come apart probably from bumping down the highway. Plugged it back together and it start right up. I crimped the connection a bit tighter and it has been problem free. Replace the fuel and air filters. I change my fuel filter every other oil change. Change oil every 100 hours.
I would pull the front cover off and check all the connections before getting a new board.

Ed McLawhorn Jr. · 10-15-2024, 08:10 PM

Thanks everyone up to this point. Brushes came today, so I installed them. Not too bad to change and now I can rule them out as the issue. Gen started fine so I decided I would let it run all night. Hoping it helps as we?re getting ready to leave for Rockingham on Thursday.

10-14-2024, 10:19 PM	#1
Ed McLawhorn Jr. Member Join Date: Nov 2008 Posts: 291 Likes: 3 Liked 18 Times in 16 Posts	Onan 12.5kw issues Need help on issues with 12.5kw diesel onan on my toterhome. Purchased toterhome in 2022 and no issues other than running rich (black smoke). Installed vent stack and gen would randomly cut off once or twice a weekend. No issues starting back and runing remainder of weekend. I didnt install stack and left storage door open for a couple races and no issues with cutting off. Recently, it has gotten worse and now cuts off 5-6 times during the weekend regardless of stack installed or storage door opened. This past weekend it was cutting off every couple hours. Most times, this weekend once it cut off, it would only start back after 20-30 minutes. Found code 45 and checked brushes today and they seemed clean. Only issue was one was much shorter than the other....seemed odd. Ordered new replacement brushes, but not confident brushes are the issue. Code 45 also indicates problem could also be pcb board. Assuming worst case, is it possible to change board without going to a onan repair dealer? Has anyone else had experience with code 45? Thanks for any suggestions. Ed

10-15-2024, 04:52 AM	#2
Bill Grubbs Member Join Date: Oct 2002 Location: Magnolia, Texas Posts: 406 Likes: 1 Liked 464 Times in 62 Posts	Re: Onan 12.5kw issues Filter change? Air? Fuel? Type of diesel (B20/no1/no2)

10-15-2024, 04:46 PM	#3
Jack Zimmerman Junior Member Join Date: Dec 2001 Location: Clemmons, NC Posts: 34 Likes: 0 Liked 9 Times in 5 Posts	Re: Onan 12.5kw issues I've been told that a pretty common failure issue on the Onan QD generators is the fuel pump power supply on the main circuit board. The symptom is that the generator will shut off randomly and it may or may not restart. Our 10K unit did it when it got hot and as far as I know, the only permanent fix is to get a new circuit board. However, an easy work around and a way to diagnose if that is the problem is to run a jumper wire from the + battery connection on the side of the generator to the fuel pump power wire which is accessible through a small cover on the front right side of the generator. If that fixes the problem you'll know it's the circuit board. And if you use that method to run the generator until you get a new circuit board (like I did), you just need to make sure you disconnect the jumper wire when you shut off the generator or the fuel pump will keep running.

10-15-2024, 06:33 PM	#4
Mike Pearson VIP Member Join Date: Mar 2007 Posts: 2,365 Likes: 559 Liked 1,725 Times in 529 Posts	Re: Onan 12.5kw issues Mine has an 8k QD Onan. One time it would not start. I took the front cover off and the spade connector for the fuel pump had come apart probably from bumping down the highway. Plugged it back together and it start right up. I crimped the connection a bit tighter and it has been problem free. Replace the fuel and air filters. I change my fuel filter every other oil change. Change oil every 100 hours. I would pull the front cover off and check all the connections before getting a new board. __________________ Mike Pearson 2485 SS

10-15-2024, 08:10 PM	#5
Ed McLawhorn Jr. Member Join Date: Nov 2008 Posts: 291 Likes: 3 Liked 18 Times in 16 Posts	Re: Onan 12.5kw issues Thanks everyone up to this point. Brushes came today, so I installed them. Not too bad to change and now I can rule them out as the issue. Gen started fine so I decided I would let it run all night. Hoping it helps as we?re getting ready to leave for Rockingham on Thursday.