PCM Troubles. Anybody run into this issue before?

Sooooo I swapped my battery out because, well, it sucked. Then, I went and reduced the sensitivity of my shock sensors because I grew tired of my stock alarm system going off for no reason.

A couple days later, I enter my car and everything is dead. Power locks won't work, interior lights won't come on, and worse yet, nothing happens when I turn the key. Even though it's a brand new battery, I measure the voltage anyway and get an even 12.5 V with no jumping around. My friend suggests I leave the + terminal disconnected for 10 min. to reset the PCM. I do this, and sure enough it starts up no problem.

This morning as I'm leaving, my stereo pops, everything cuts out, and my engine stalls. I restarted it and made it to work. Then at work when I get in at lunch, the power locks work, dash lights come on, but when I try to start it, the starter starts to engage for a split second then everything cuts out. Again, I disconnect the battery and she starts up a little later, though a little rougher than normal.

On the way home I monitored my running voltage, which hung around 13.9 and dropped very briefly to 13.7 when stopped.

Back at home, I go to start my car. Everything works. Try to turn over the engine and EVERYTHING cuts out. No lights or anything come back on. Everything is dead. Disconnected the battery yet again, and she's sitting like that til morning.

I'm thinking my PCM is screwed. Which is a good excuse to get a tuned one.

If you don't think it's my PCM, let me know so I can put the money towards resolving this issue.

If you think it is my PCM, what version is the best bang for your buck? I don't plan on getting too fancy - intake, smaller pulley, and exhaust is all I want at the moment. So ZZP? Wbodystore? Overkill? Other? I'm leaning towards Overkill since I am in Canada.

Thanks.

I doubt its your PCM.

You have some sort of wire issue going on here, I like to blame aftermarket alarms.

Don't have an aftermarket alarm. Completely stock. Did put in a new stereo, but I checked the wiring today. It's all fine. Plus this issue started before I put in the new stereo.

Another thing I forgot to mention. After the first day it happened, I unlocked my car. The factory alarm disarmed, I started it and the %$%#% factory alarm started going off. i hit the unlock button on the key fob and it stopped honking.

Security light flashing?

Wasn't when I opened the door. As for after it was running, I didn't look. But it was doing the honks that I know so well from when it would go off in the middle of the night.

What are you driving?

i would check for a grounded lead wire to rule out a wiring job.

More info please. Year make n model. Any aftermarket installs, such as autostart etc. Any work done recently...

1998 Pontiac Grand Prix GTP. Nothing aftermarket at all. All this happened after I switched out the battery and reduced the sensitivity of the alarm using the method outlined in the owner's manual.

Most recent work would be front rocker gasket, supercharger oil change, and wheel alignment.

Threw a code for the EGR valve recently.

Car is completely dead today.

Oh also new halo headlights.

Ok, power for locks, seats, headlights.. none of that goes through the pcm. Pretty sure we can rule it out. All this power and control of these various things does go through the BCM or body control module.

However...you appear to have a draw or other issue if you are finding the battery dead. I would double check that the the power cable from the alt is snug. Check the voltage etc of the battery, is it dead or is it just not supplying power to the car.

my guess would be corroded battery cables or bad terminals in the new battery. I also guess that unhooking the batt cables isnt resetting anything its just getting a working connection to the battery again when you reconnect them. Try to wiggle the cables when its acting up and see if it works or try a different battery.

Battery is not dead. I cleaned the terminal out and the bolt off as well because it was corroded. I have tried wiggling the cables but I will try again more thoroughly.

If you had enough corrosion to have needed to clean it. Next time you pull the cables. Take the bolt out and slide the rubber boot off. Is the crimp from the connector to the cable green and in questionable shape? it might be time for fresh cables.

Didn't need to clean it, I decided to while I had it disconnected. But I will check the cables because it doesn't hurt to look.

Originally Posted by BillBoost37

If you had enough corrosion to have needed to clean it. Next time you pull the cables. Take the bolt out and slide the rubber boot off. Is the crimp from the connector to the cable green and in questionable shape? it might be time for fresh cables.

I would like to let you know, sir, that you were 100% correct on this. The old battery was leaking acid everywhere and it corroded the connection to ****. A good cleaning and some baking soda and water seems to have resolved the issue.

My friend took one look and diagnosed it before I even mentioned it to him. Looks like I learned something new today.

Thanks for your help everybody. <-- That's me, embarrassed.

Glad to hear you found it and got it straightened out.

You realize..we only know this one, because it's likely happened to us.

Originally Posted by BillBoost37

You realize..we only know this one, because it's likely happened to us.

+1,000! Lol...