kohler 17RES OS overspeed fault

[electrofelon]

Probably a long shot, but anyone have experience with this fault on this or similar unit? Its a circa 2007 unit. It cranks for about 4 seconds, just starts to fire then stops with a overspeed fault. I am nearly certain that it is not actually overspeeding. I tested the speed sensor and both tests pass with the 1.3-1.9 k ohms and 1.75 VAC minimum while cranking. I am leaning toward it being the controller, because when I disconnect the gas so the unit does fire at all, it cranks for about the same 4 seconds then stops with an OC (overcrank) fault and does not try again. According to the service manual it is suppose to crank for 15 seconds, stop for 15 seconds and do that 3 times. Apparently that is built into the controller and is not adjustable.

 

[Birken Vogt]

Your logic sounds about right. The only thing I would do differently is to use a spare controller I have, but you do not have that luxury.

 

[qcroanoke]

Your logic sounds about right. The only thing I would do differently is to use a spare controller I have, but you do not have that luxury.

We did that with Onans. Usually we would have 2 or 3 to start in our facility and if we had a problem with one we would go get the card out of one we had already tested and see if the problem went away. If it did a card was ordered and we tested the generator when it came in.

 

[electrofelon]

Your logic sounds about right. The only thing I would do differently is to use a spare controller I have, but you do not have that luxury.

LOL, you actually replied to a thread on a different forum back in 2015 on this same issue on a 12RES. In that case it was the magnetic pickup. IT seems he got the 1.75 AC min voltage but got open with the ohm test..... so unless they do something weird like calculate the 15 second cranking time off the magnetic pickup, then seems like the controller.

 

[Birken Vogt]

You made me go read the manual, and it is true that a dead MPU would result in 4 seconds of cranking and then OC.

So I would use needle probes to make sure that the MPU signal is making it all the way to the pins on the controller before condemning it.

 

[electrofelon]

You made me go read the manual, and it is true that a dead MPU would result in 4 seconds of cranking and then OC.

So I would use needle probes to make sure that the MPU signal is making it all the way to the pins on the controller before condemning it.

Yes I stumbled across that too. There is one set of connectors betwixt the MPU and the board. I did the electrical tests at the connectors. Then I unplugged the connector from the board and tested continuity between that and the midway connectors. They tested fine. Perhaps I could try getting it at the board connector just as a double check. That would be hard without the right small probes though.

I wonder if the MPU could pass the resistance and voltage tests but still be bad?

 

[OldBroadcastTech]

LP fired ?? If so check for sticky throttle shaft......LP tends to gum up the works

 

[Birken Vogt]

LP fired ?? If so check for sticky throttle shaft......LP tends to gum up the works

That would not give the symptoms listed.

 

[electrofelon]

LP fired ?? If so check for sticky throttle shaft......LP tends to gum up the works

Shaft moves freely and the stepper moves it from closed to fully open as it should