voltage spike - JKowners.com : Jeep Wrangler JK Forum
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post #1 of 4 Old 01-09-2020, 04:28 AM Thread Starter
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Thumbs down voltage spike

I have a 2008 jk.. When I start the jeep its idle is at 12.7 volts and when I accelerate from a stop or rev the engine in park the volts go to 15+. Its causing the sub to cut out. I bought a new sub and a new head unit and the problem is still there. I have had the sub reinstalled 3 times and makes no difference. One thing I have noticed is when the dealer flashed the pcm the volts went back to normal. Same thing when i disconnect the battery. They drop back to the 13.8 to 14.3 range, but after it sits overnight the high voltage comes back... I replaced the alternator and the battery. no error codes to speak of. Any ideas? There is not a single thing grounded to the battery. All to the chassis like its suppose to be. The battery is full at start up too. I took it to the dealership and naturally they want me to spend 1200 on a new pcm. I dont think thats it because its never flashed an error code. I even contacted jeep and they had no solutions either.
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post #2 of 4 Old 01-09-2020, 05:23 PM
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I would double check all connections, grounds and the battery terminals, as well as the cable connections at both ends.

The voltage regulator for the alternator is built into the PCM, so there is a possibility that is the issue.
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post #3 of 4 Old 02-17-2020, 10:54 PM
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Check for loose connection in the relay box.
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post #4 of 4 Old 02-18-2020, 05:01 AM
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x2 on the PCM... although you can get a reman one and swap it yourself.

I got one from these guys after numerous issues with O2 codes.


'76 CJ-7, '43 CJ-2a, '78 Bronco,'78 CJ-7, '75 CJ-5, '78 CJ-7, '80 CJ-7, '78 SJ, '79 SJ, '78 and a '76 FJ-40 , '90 XJ, '91 XJ, '86 CJ-7, '95 ZJ, '68 CJ-101 Commando, '00 TJ, '68 M-715, 2 '86 Military Blazers, '96 LR Discovery, '86 CJ-7, '91 YJ, '99 TJ, 07' JKU Rubi, 1988 YJ, 1973 Commando, 3 Diesel Excursions....
Now back to a 2013 JKU Rubicon with "stuff", planning 37's with minimal lift.

I've tried them all... Jeeps are still the best. (0||||0)
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