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Short in PCM Constant Power Circuit

Old Jan 6, 2009 | 02:28 AM
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Default Short in PCM Constant Power Circuit

My PCM constant power keeps shorting but all switched power sources show no issue.

I pulled the wires from the harness and attempted wiring it directly to the battery with an inline fuse. It still shorted.

I am completely lost as to what could be causing this other than a bad PCM.

Any ideas or suggestions as to how to diagnose the problem.
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Old Jan 6, 2009 | 01:14 PM
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Is it blowing the fuse and what size fuse are you using?
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Old Jan 6, 2009 | 01:17 PM
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Yes the fuse is blowing.

I had a 5 amp fuse for safeties sake, but it was then replaced with a 20 amp just like in the OEM fuse box.

They both blew.
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Old Jan 6, 2009 | 06:04 PM
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Have you tried unplugging both PCM connectors and then hooking the power up to it to see if the fuse blows. If it blows without the PCM it has to be in the wiring, if it still blows then I would try another PCM. Never heard of this before, but stranger thing have been known to happen. Good luck.
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Old Jan 6, 2009 | 07:05 PM
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you would probably get some better advice from the pcm diagnostics section. there are alot of tuners that visit that section. id post this problem there also.
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Old Jan 6, 2009 | 07:13 PM
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I did not try powering the harness without the PCM.

However, I know the 12+ constant wires are not grounding to any others. I pulled them out of the harness all the way back to the PCM connector.

When the PCM arrived after being programmed it package was pretty badly damaged. It sounds like something is shifting inside the housing when I shake it slightly. I called my tuner about this and was told the sound from inside the housing was normal.

The PCM is on its way back to get checked out and the harness is now out of the car.

I am hoping the PCM is the problem, but to be safe I am bringing the harness back with me to school. My roommate (EE major) and I are going to give it a thorough once over. I guess we are just going to have to go wire by wire checking for shorts, and confirming the grounds are good.
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Old Jan 6, 2009 | 10:06 PM
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It sounds like there's something loose inside the PCM? I've never heard anything 'loose' sounding in any of mine. Might have been damaged in shipping?
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Old Jan 7, 2009 | 04:44 AM
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Hearing something loose/shifting inside the pcm IS NOT normal. Try another pcm.
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