Fried pcm?

psduser1 · Oct 31, 2016

So I started with a nostart condition, on this late 99/00 pickup. 260k miles, zf6.
Replaced the starter, the relay on the fender, and the clutch interlock switch, mostly due to their age, and relative cost. Throwing parts at it, in other words.
When I go to mount the starter-with wires attached-the starter engages, i.e it's powered. That's what led to the relay, and clutch interlock switch replacement, BTW.
After talking to a buddy, he suggested a failed gem. Possible, as I did have a leaky windshield a few years ago. So I pulled the fuse panel/gem, absolutely pristine.
I put the fuseblock/gem back together, and reassembled everything under the dash, and now I have no power anywhere in the fuseblock, or at the fuseblock under the hood.:cursing:
Everything went together easily, no problems.
Unfortunately, halfway thru putting everything together, I realized the batteries were connected.
Is it possible or probable that I fried the pcm?
No power at key on, no power at any fuse, tested with a multimeter.

co04cobra · Oct 31, 2016

I have took GEMs in and out before with batteries hooked up with no problems.

Not saying it couldn't cause a issue, but I don't think it would cause no power anywhere.

Also, the truck will still have power on most everything with a bad pcm, or even the PCM completly removed.

The fuse box under the hood is powered from straight 12V iirc. You should have power in that box as long as you have batteries hooked up.

psduser1 · Oct 31, 2016

Just double checked, all the connections appear tight, and no power anywhere.
I am at a loss.

mikeeg02 · Oct 31, 2016

Do you have power under the hood at the solenoid on the fender next to the vacuum pump? I know if the one terminal comes lose at that solenoid the dash goes dark, and motor shuts down.

psduser1 · Oct 31, 2016

:cursing:
:lookaround::doh:
Man I feel dumb, had that unhooked while trying to isolate my starter problem.
Hooked it up, power is back on to the dash.
Thank you for pointing me to the simple problem.:toast:

mikeeg02 · Oct 31, 2016

:blitzed:

It happened to me once while driving down the road. After a motor swap. haha Ill take an easy fix any day!

psduser1 · Oct 31, 2016

Yeah, me too.
I'm still working on the starter issue. Pulled the positive wire, and no obvious problems. Continuity checks out good, but it's getting a new one, regardless.
Can't find any reason why both posts are hot at the starter, yet.

Arisley · Nov 1, 2016

Ignition switch?

mikeeg02 · Nov 1, 2016

I re-read your OP, when you touched the starter to the frame and it spun the starter, I am assuming you also checked the small wire for voltage? (which is probably why you replaced the other parts but I just want to make sure there was voltage on the small signal wire) If there was no voltage there, and the there was still power on both large posts, the solenoid on the starter could be stuck on.

psduser1 · Nov 1, 2016

Arisley said:
Ignition switch?

I pulled the column apart, and everything appeared to move freely.

mikeeg02 said:
I re-read your OP, when you touched the starter to the frame and it spun the starter, I am assuming you also checked the small wire for voltage? (which is probably why you replaced the other parts but I just want to make sure there was voltage on the small signal wire) If there was no voltage there, and the there was still power on both large posts, the solenoid on the starter could be stuck on.

Had the starter checked on the bench, it seemed to be a-OK.
I'm going to put the new positive cable on and start rechecking everything.

mikeeg02 · Nov 1, 2016

psduser1 said:
I pulled the column apart, and everything appeared to move freely.

Had the starter checked on the bench, it seemed to be a-OK.
I'm going to put the new positive cable on and start rechecking everything.

Your starter should have a big wire and a little wire right?

Also, there are two large posts. You cannot use the one that has an existing wire going to it(that goes to the starter motor), as that will put battery power directly to the starter motor. You must use the empty large post for the battery connection. Not trying to be cynical or malicious, just re-emphasizing.

psduser1 · Nov 1, 2016

mikeeg02 said:
Your starter should have a big wire and a little wire right?

Also, there are two large posts. You cannot use the one that has an existing wire going to it(that goes to the starter motor), as that will put battery power directly to the starter motor. You must use the empty large post for the battery connection. Not trying to be cynical or malicious, just re-emphasizing.

Lol, I know that, and I assume you meant that as gentle reminder.

Having said that, I actually had this all together last night, and everything seemed as it should. Since I already had the pos cable on the way, I might as well change it. And did.
Bam. No start.
All the wiring is correct after another double check, no power anywhere.
Arisley called it. Ignition switch, and everything is happy again. Never would have thought that, as the lock cylinder mechanism moved freely. Two experienced mechanics called "not likely" on the ignition switch, and in fact one said he'd replaced more gems than switches-leaky windshield problems.
The intermittent part got me, also, as one time the switch worked, or three times, then it didn't.
I believe I have it fixed now, with approximately 10x the actual cost, lol. On the other hand, I learned something.