Mechanics

WON'T START DUE TO CRAZY ELECTRICAL PROBLEM

2001 Chevrolet Express • 250,000 miles

Put key in, turn to (2) position and everything sounds normal. When I try to start it just a loud click then everything goes dead. I move key back to (2) position. Then the instrument cluster/interior light module clicks loud sometimes and sometimes not loud, the reminder buzzer will fluctuate in sound, headlights, tail lights, brake light will not work, no lights on the inside will work, I move the brake light sensor around and it changes the sound of the clicking and buzzer. I then can move the main wiring harness around going into the pcm under the hood and it sometimes make the2 noises change and the lights work. I can pull the pcm large fuse out of the fuse box next to pcm and everything will go back to normal until I try to start it again. There is a strange power drain on battery while this is happening. Battery holds 12.8V normally. While this is happening the voltage will fluctuate 10.8-11.5. While it's acting normal voltage will stay about 12.8. I have plugged in a computer scanner. While key in (2) position it reads everything normal. When I try to start it the scanner goes dead. This started after the hydroboost was replaced. A lot of fluid had leaked onto pcm before hydroboost was replaced. It ran for about 5 minutes after hydroboost was replaced. I need any and all ideas anyone may have. I think it might be the pcm but scanner didn't show any P0600 codes.
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Futant
May 1, 2013.



I forgot to say it is a 3500 series with a 5.7L engine
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Tiny
Futant
May 1, 2013.
Everything you described sounds typical of a bad connection on a battery cable or where the smaller positive wire bolts to the under-hood fuse box. Finding this should be easier since you can get it to go to the bad condition. Turn the headlights on so some current is always trying to flow, then start right on the battery bolts and measure the voltage. If you find 12.6 volts, move one meter probe from the negative post to a paint-free point on the body. You should find the same voltage. Move the probe from the positive bolt to the stud on the fuse box. You're looking for the first place the voltage is considerably lower. That will be the point of the bad connection.

Caradiodoc
May 1, 2013.
Thank you for the advice. I will do that when it slows down raining here.

Tiny
Futant
May 4, 2013.

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