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I did a search on here for replacing the engine computer and was surprised for not finding much !

We have an 05 Silverado with a 5.3 in it. The other evening, my wife went to see a friend and when it began to storm, she decided to leave. She went out and the truck was dead, no click, no crank. I went to get her and tried to jump start it (while it was still storming) and arcs came off of the negative terminal when the cable touched it. I stopped and decided to disconnect the battery till morning. Next day I go over there and reconnect the battery and the engine fans start running with no key in the ignition (probable reason why the battery arced the night before)! Battery voltage was down to under 11 volts so I took it to get checked since it was 5 years old. Got a new one, connected it, the truck fired up, and all seemed well. Took the truck home, parked it and 2 hours later I go to leave in it and the engine fans are running again ! When I drove away, I got about a mile from the house and the check engine light started flashing. Codes that came up were P0300 and P0480, random misfire and engine cooling fan code error.

So..... I checked what I could, but then on Monday took it to an automotive electrical guy. He ran his diagnostics and while it was there, the fans came on by themselves again with no key on. He check his schematics, ran his checks and suspects the computer has some kind of fault. He said to get a salvage computer and he would re-flash it for my VIN.

I checked around and found one local, but also looked online and came across "All Computer Resources" in Miami FL that sells reprogramed ECM / ECU / PCM automotive computers.

I wasn't sure what to do, so called another electrical repair guy for another opinion. He said it could well be the computer, but would run his own checks before just replacing it. He was adamant about not using a salvage or reconditioned computer. Said he has been there, done that, and will now ONLY install new OEM replacement GM computers and flash them.

Anybody out there have good or bad luck with a reconditioned computer ? Any thoughts or suggestions ?

Edited by T-Town-Z
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Yeah, I'm not crazy about the thought (or price) of changing out the computer. The main issue is the engine fans coming on randomly with no key turned on. Its hard to find a really good electrical guy.....

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CB's and fuses for the fans are good. Looking for any shorts is the harder part. The first guy I took it to had it on his scope and didn't find anything.

Any idea where or how many grounds there may be ?

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  • 2 weeks later...

I found another shop that someone recommended to me. They finally diagnosed it as the computer being bad. It had moisture inside it and he also showed me about 8 of the wire connectors that were coated white with corrosion.

They cut out, then soldered in some new wires with connectors and replaced the computer with a new unit from GM. $800 later the truck is running and behaving properly again !

In discussing it with him, he said that of all the (GM) computers he has changed out over the years, only 2 were not trucks. His thinking was that with GM placing some of these computers low (below the battery) and just fwd of the drivers tire, it gets enough water spray up there to corrode the terminals and for water to get into the unit.

My thinking is "Brilliance in Engineering" on GM's part to put computer down there on a 4WD truck !!!

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