Truck wont start after unhooking PCM [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: Truck wont start after unhooking PCM


hardtrailz400
10-21-2009, 09:28 PM
I picked up an extra PCM off ebay to run while I sent mine in to PCMforless, but when I took mine out and installed it, I couldnt get it to run the truck. I did the security relearn procedure with 6 attempts and decided to just put mine back in until I could leave my truck down for a couple days and send it later.

However, after reinstalling my PCM, the truck will not start. I tried the security relearn, but the security light has not been on. It justs cranks and cranks, but will not run. I am at a loss, I even tried hooked up the fiances car with jumpers cables to make sure the battery had plenty of juice, but nope, no start.

Help. I am at a loss. I do have the codes 0122 and 0223 showing up on my scanguage, but do not understand why the truck will not run.

MAY03LT
10-21-2009, 09:43 PM
Did you do anything to the throttle body today? Do you have any freeze frame data for the codes?

The pcm can, under certain circumstances, prevent the engine from running with either of those codes active.

hardtrailz400
10-21-2009, 09:48 PM
Now the codes show 0412 and 2432 and the others stayed gone after I cleared them

hardtrailz400
10-21-2009, 09:49 PM
Did nothing other than install a new cd player before messing with the pcm, but truck was fine after the cd install. Cleaned Throttle body a couple months ago.

the roadie
10-21-2009, 10:29 PM
Was it guaranteed working when you bought it? Junkyard or private seller? Part number and year match?

WOOLUF1952
10-22-2009, 02:55 AM
The first thing that comes to mind; check all the pins in both of the PCM's. There may be a bent pin.:m2:

hardtrailz400
10-22-2009, 10:44 AM
The first thing that comes to mind; check all the pins in both of the PCM's. There may be a bent pin.:m2:

I glanced, but will double check.

I unhooked the battery overnight with the stock PCM in it. After work I will hook up the battery and try it out.

n0kfb
10-22-2009, 11:06 AM
If it's cranking, check the basics.

Make sure all connections to the PCM are tight. Remove and reconnect the connections to the PCM. Then if it still doesn't start, I'd check for spark. If spark was good I'd check for fuel.

Do you have a scan tool? Are there any codes pending?

-- Dan Meyer :steer

hardtrailz400
10-22-2009, 11:49 AM
If it's cranking, check the basics.

Make sure all connections to the PCM are tight. Remove and reconnect the connections to the PCM. Then if it still doesn't start, I'd check for spark. If spark was good I'd check for fuel.

Do you have a scan tool? Are there any codes pending?

-- Dan Meyer :steer

I posted the codes, but everytime I clear them, they come back different.

I checked the connections, but will again. I killed the battery trying the security relearn, but the security light is not even on.

n0kfb
10-22-2009, 02:12 PM
Once again, check the basics. Do you have spark? Are the fuel injectors metering fuel?

One thought that occurred to me is since you get seemingly random trouble codes, you have poor electrical connections somewhere. Since you were working on the PCM, check those connections again (yes, I know you say you've done that...). Check your connections at the battery also. One other thing that is a longshot is you have a bad ignition switch.

-- Dan Meyer :coffee

hardtrailz400
10-22-2009, 02:24 PM
I will try the connections again tonight and make sure the battery has good connections. They are the only two places I touched.

I did decide to go ahead and do the core program at pcmforless.com so I can get a tuned pcm this weekend and know that the pcm is not the issue. Cost a bit more, but they are trying to help me out.

If the security light is not on....Is there any reason to do the security relearn or just look for another problem. I would really like to have it running with the stock pcm before the other one gets ere so i can see the difference back to back.

I do know i will need a case relearn now, but I got it lined up to be done Monday at the Chevy dealership.

Thanks to those trying to help me.

hatchet669
10-22-2009, 02:25 PM
random multiple codes... sounds PCM to me... doesnt fit the characters of a ignition switch... did u disconnect the battery while taking it out? lol

check list i would do...

check every single pin on the connector... check the ports on the pcm... check to make sure they are seating properly...

i started my truck before when one of the connector wasnt seated correcly... man that was a scary moment...

and as roadie said.. did the pcm come out of same year set?

hardtrailz400
10-22-2009, 02:35 PM
random multiple codes... sounds PCM to me... doesnt fit the characters of a ignition switch... did u disconnect the battery while taking it out? lol Yes I did

check list i would do...

check every single pin on the connector... check the ports on the pcm... check to make sure they are seating properly... Will do after work

i started my truck before when one of the connector wasnt seated correcly... man that was a scary moment... Please explain

and as roadie said.. did the pcm come out of same year set? I am not using the other one. I am trying to use the factory one, so it doesnt matter about the one I had bought. It is out of the picture now

hatchet669
10-22-2009, 06:20 PM
no it is still in the pic... if u bought from a different set year... the pins do go to different parts.. just a random example... on one year model a pin may go for starting.. but on another year set.. the pin mite be AC... it could be possible that screwed up somethign along the line... the pcms changed (someone correct me if i'm wrong) 02-03, 04-05, 06-07, 08-09.... i could be wrong but i think every 2 years there was a change to the pcm...

what happened was one was plugged in all the way.. it started but ran like a dog.. made horrible noises, bunch of dash lights...

ylab
10-22-2009, 06:40 PM
Couple of thoughts come to mind:

First, are you sure the connectors are in the corect order? - There's a White one, a Gray one and a Blue one. At least in '02-'03 that's the order they connect in from left to right when looking directly at the PCM. (Not sure if the color order changed in later years).

Second, the connectors are sometimes a real PITA to install. You need to push strait in the connectors as you snug the retaining screw. If they're not in all the way OR you bend the ground spike at the center of each one, you end up with a no start (or lumpy running) with all sorts of random codes.

Hope this helps, as it sounds like either they're on on correctly or out of order.

Edit: Even after a security code relearn of the new/purchased PCM, the original would still have the correct values to allow a crank/start. So unless the security light illuminates, its absolutely not that.

hardtrailz400
10-22-2009, 07:32 PM
Ebay one out of pic, because i will not use it. I may just toss it in trash.

The stock one I will check the pins as soon as rain lets up. Seems to be the most likely issue is a pin is bent or not connected all the way.

hardtrailz400
10-23-2009, 07:37 PM
I had broke the little plastic tabs off the center plug, so I wasnt getting a good connection. I got w pcmforless and got a new tuned pcm that is about to go in, so it should fix my problems.

FYI--If i run a ziptie around to hold the plug tight or hold it by hand it will run with the stock pcm.

dsvietro
02-05-2011, 03:17 AM
how did u fix it? i left for work this morning and tried to put the truck in drive from reverse but shifter kinda lost responsiveness so i turned it off then tried to restart but no luck.. at first like i was stuck in gear but i can remove the key and now cannot move shifter im wondering if it could be linked to the radio i installed, even know i spent 150 bucks on the wire harness it self?. batt charging right now and can hear pins moving in the pcm but will have to wait to check since its late... really wishing i wouldnt have bought this truck even tho its so nice..

the4biddendonut
02-05-2011, 10:44 AM
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