Onan Code 27 diagnosis help.

Cummins/Onan Air Cooled & Liquid Cooled standby generator troubleshooting and repair questions
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Joined: Tue Mar 24, 2020 10:04 am

I have an Onan Quiet Diesel 10k - Model 10HDCKA11608C. It is 12 years old. Tries to start it the other day and its started but quit right away. It is giving me code 27 which is VAC Sense Loss. The service manual states the issue is with the control board or the voltage sense transformer. The service manual states to disconnect the harness from the controller and check resistance at pins 33 & 34, does not state if I should be doing this check on the harness side or the controller side so I did both. Manual states I should be looking for an ohm reading of 586. On the harness side I get nothing. on the controller side, my autoranging multimeter is telling me 8.95 miliohms. I do not understand this well enough to know if this is grossly out of range or not?

The manual goes on to say to test the two windings of the voltage sense transformer, one side is to have 2045 ohms and the other side to have 586 ohms. I get open loop on both sides. This makes me think I am not doing this right. Seems strange to me that both sides could be toast.

If anyone has any insight they could provide it would be much appreciated. Best regards, Aaron.
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Joined: Thu Nov 15, 2018 4:19 pm

8.95 milliohms is 0.00895 ohms. Another description of that is a short circuit.

It is 65,475 times lower than it should be. (586/0.00895)

Are you sure the probes weren't touching each other?
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