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#547 - 09/10/14 01:23 PM Dealing with Onan Generator Fault code 27!
Muniac Administrator Offline

Registered: 11/12/08
Posts: 247
Loc: Livingston, Texas
I usually run the generator about once every 1-2 months just to warm it up. I did so about 2 weeks ago without problems. One day we had a power outage and I went to start the generator only to be greeted with fault code 27 which means "PMA sense lost fault." PMA stands for permanent magnet alternator. Not usually a good condition as it means either the stator or the inverter/converter unit failed. Both are expensive and not easy to get at.

Luckily Lehighton, PA is near a lot of industry. I found Engines, Inc. in Northampton which is about 1/2 hour away. Given we live in the vehicle, it's somewhat of a hassle to drive it out for service. Engines, Inc. can easily do the work but they can't provide any hookups. Not even electricity. With some apprehension, I decided to tackle this repair myself. It's by far the most difficult repair I've done in the long laundry list of DIY repairs I've performed over the past 7 years. That said, it's manageable without special tools. I decided the inconvenience of relocating and shutting down the refrigerator clearly offset the DIY repair efforts. John Burger at Engines, Inc. was delightful to deal with. I've documented this in the above hyperlink.

Just getting into the repair.

I was able to obtain the diagnostic procedure for fault code 27. It basically requires you to do a simple load test to clear the fault. Failing that you check the stator output voltages. Should be 20VAC RMS across each phase while cranking. Don't crank the generator for more than 30 seconds. Too much cranking will damage it from heat. If the phase voltages are fine, you need to replace the inverter/converter unit which is a $2K part. Not much choice in the matter as the unit isn't serviceable.

The slide out tray makes getting at the generator reasonably easy. On some vehicles, the generator is buried behind a small access door which means all 420 Lb of it needs to be removed completely for inside repairs. And anything in its way needs to be removed first. Luckily I didn't need to go down this road. Also the out of level site we're parked in required me to put blocks under the front wheels. That helped increase clearance under the generator.

My permanent magnet rotor is in good shape.

My stator is also in good shape.

A bad inverter/converter unit was the problem. A $2K part!

Anyway I took a deep breath and started taking things apart. Driven partially by wanting to visually inspect the generator just to gain some confidence. The breakdown could have happened at a much worse time and place. Like cold weather and/or in a remote area with difficult access to a good parts/service place. I performed both the Service Manual diagnostic tests and visual inspections to my satisfaction. That culminated in a confident diagnosis of a bad inverter/converter unit. At $2K one wants to be sure that's the problem.

I also found a cracked coolant expansion tank. I took care of this along the way. The oil fill line runs through the expansion tank which means that needs to be removed. I also changed the engine oil and replaced the coolant with new diesel rated antifreeze. The expansion tank coolant return hose was badly crimped so I replaced that too. It isn't within the main coolant circulation loop. Just the same, I didn't want to put the generator back together with a crimped hose. The hose clamps are all crimped so they need to be cut and replaced with combo-hex band clamps. Use a pair of heavy duty wire cutters to make the cuts. BE VERY CAREFUL to not let any of the pieces land in the generator. The magnets in the rotor are very strong. Same can be said for any screws you'll remove taking things apart. I keep count of all these to make sure nothing is missing. Handle them carefully. If something lands in the generator you'll have a hell of a time getting it out.

The parts were here in 24 hours. While I was waiting, I vacuumed out all the dust, leaves and debris from inside the cabinet. Just a good housekeeping measure.

Crimped coolant return hose. Not serious.

New inverter/converter unit installed.

I worked on this over a number of days totalling up about 10-12 hours of labor. My pace is slow given this kind of work places me in unfamiliar waters. The photo above was taken just before my first attempt at a no load test startup (generator breaker open). My stomach dropped when I got back fault codes 17 (Fuel pump fault) then 19 (Actuator shorted or open). It turns out the connectors on the inverter/converter require a really hard push to seat them. I hadn't pushed them in hard enough so some of the pins weren't connected. Once I seated the connectors properly, the generator fired up without problems.

The generator produces two 120 VAC circuits rated at about 33 amps each. I measured the output voltage between each of these outputs back to neutral. Unlike utility power that comes from a transformer, the "outside" legs of the generator are in phase. Meaning the sum of the currents from both circuits (red and black wires) are pulled through the neutral leg (white wire). So it's impossible to get 240 volts from the generator as would be the case on the outside legs of a utility transformer or 50A hookup.

Some people have had problems with their fuel lines leaking owing to the rubber drying out and cracking. Mine seems in good shape. They claim this can create erroneous fault codes. There is a fault code 36 which is an "Unknown shutdown fault". This means the generator just stopped without any command from the controller. The diagnostic says to check the fuel supply since fuel supply line leaks are covered by fault code 36. Connections to Silver Leaf monitoring devices have also been reported to cause erroneous fault codes. I've not had any experience with these.

In my case, I simply removed everything from the generator before performing any testing. Essentially disconnecting it from anything in the vehicle. I couldn't get the 27 code to clear. So I was 99% sure the inverter/converter was bad. And this turned out to be the case.

So I'm back up and running at this point. I did about 1 hour of load testing to include hair dryers, A/C units and heaters. All seems fine. I rate this repair as advanced and not for those that aren't handy with tools and mechanical devices. I was glad to be able to follow this one through. At times I felt way in over my head but I hung in there and moved through the steps slowly and carefully. I didn't need any special tools either other than a set of Torx wrenches which I already have.

If you can get a copy of the parts and service manuals they are a BIG help. The generator issues fault codes by blinking the light within the start/stop switch. A crude system but effective. I've documented how the blinking works HERE. The codes are documented in the Service Manual. Feel free to email with any questions, suggestions and/or comments. I hope this article is helpful. Safe travels and keep the lights on! smile

Complete slide show HERE. (15 frames w/captions)

My genset is: Onan 8K Quiet Diesel (circa 2005)

Model: 8HDKAK-1046J
S/N: H050823805

The first character of the serial number is the month it was made. The second two numbers are the year it was made. So my unit goes back to August 2005.
Evolve and simplify!
Scott Bridgman, Why not join and post your own comments??
scott@muniac.com (email me)

#552 - 09/21/14 05:54 PM Re: Dealing with Onan Generator Fault code 27! [Re: Muniac]
Muniac Administrator Offline

Registered: 11/12/08
Posts: 247
Loc: Livingston, Texas
I noticed my hours meter froze at 739.2 hours. So I needed to replace that as the last thing to wrap up the generator repairs. I have no idea when this failed so the exact hours on the generator aren't known. I don't think it's too far off since we don't use the generator that much.

I was able to replace the hours meter by taking the top cover off only. There is a plastic retention ring that has a ratchet step in it similar to a wire tie wrap. It let go pretty easily when I pushed the meter out through the back. I carefully connected the new meter's wires making sure to get the polarity right. Reaching in through the back I could push on the retention ring to secure the meter. So now I've got service interval information once again. Albeit starting from 0.
Evolve and simplify!
Scott Bridgman, Why not join and post your own comments??
scott@muniac.com (email me)


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