PCM Bat Fuse - what does it do?
Thread Starter
Joined: Nov 2001
Posts: 32,987
Likes: 58
From: Houston, TX
PCM Bat Fuse - what does it do? I remember in the old days, prior to having custom tuning available, we used to pull the "PCM Bat" fuse under the hood and it would 'reset' things, sometimes causing us to run quicker on the next pass down the dragstrip.
Anyone know off hand what that fuse is for? Also, should I still be able to read/flash a PCM if it is removed? I'm having some quirky wiring issue with a car, all of my lights stay on if I leave that fuse in, and my ignition switch doesn't do anything. I pull the fuse, and my lights go off and the ign switch works again, and I can turn the lights on/off like normal. I even could read and flash the PCM with that fuse removed.
weird stuff.
Anyone know off hand what that fuse is for? Also, should I still be able to read/flash a PCM if it is removed? I'm having some quirky wiring issue with a car, all of my lights stay on if I leave that fuse in, and my ignition switch doesn't do anything. I pull the fuse, and my lights go off and the ign switch works again, and I can turn the lights on/off like normal. I even could read and flash the PCM with that fuse removed.
weird stuff.
when I disected the harness in my car, the PCM Bat fuse was a direct constant 12v supply to the PCM. Unfortunately, other than that I don't know too much about it... there were a couple of constant 12v wires that went to different pins of the PCM, and several ignition 12v wires that went to the PCM.
Thread Starter
Joined: Nov 2001
Posts: 32,987
Likes: 58
From: Houston, TX
does anyone know if the car will start/run with the PCM bat fuse pulled? I can't check that right now because I have the exhaust system and headers off the car
The bat fuse is like the backup battery in your alarm clock. I've never tried to run or flash it while removed.
It almost sounds like you have a wiring/grounding issue. I've seen loose grounds cause all sorts of issues. Low batteries can also cause odd faults.
It almost sounds like you have a wiring/grounding issue. I've seen loose grounds cause all sorts of issues. Low batteries can also cause odd faults.
Staging Lane
Joined: Aug 2005
Posts: 94
Likes: 0
Originally Posted by SmokingWS6
The bat fuse is like the backup battery in your alarm clock. I've never tried to run or flash it while removed.
It almost sounds like you have a wiring/grounding issue. I've seen loose grounds cause all sorts of issues. Low batteries can also cause odd faults.
It almost sounds like you have a wiring/grounding issue. I've seen loose grounds cause all sorts of issues. Low batteries can also cause odd faults.
Will it start up and run?
You're not using LS1edit, are you ??
If it's the '98, the PCM can get a checksum error stored, and , even though it will seem to program normally, it won't ever work again. That's what happened to mine. I even sent it Jesse Bub to have the PCM recovered, it still would not work.
Thread Starter
Joined: Nov 2001
Posts: 32,987
Likes: 58
From: Houston, TX
The car flashed and started up just fine yesterday, with the PCM bat fuse removed. Not sure what the fuse is for, but the car runs like normal without it. weird 
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Originally Posted by Nine Ball
The car flashed and started up just fine yesterday, with the PCM bat fuse removed. Not sure what the fuse is for, but the car runs like normal without it. weird
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