Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner
1 - 14 of 14 Posts

·
Registered
2003 chevy trailblazer_ltz
Joined
·
43 Posts
Discussion Starter · #1 ·
I have a 2003 LTZ 4,2. I thought I had read somewhere that the car should have power at all times or it will ruin the PCM. Is this true? I've had the car since it was new. I have had some strange things happen when there's just the slightest bit of corrosion on the battery cables. I have had to replace the transmission 5 times. Could the PCM be bad? How would I know if it needs to be replaced.
 

·
Premium Member
2004 chevy trailblazer_lt
Joined
·
3,229 Posts
Well, that's a new one for me. As far as I know, the PCM (or ECM if one cares), will be wired from the factory such that it will be connected to battery voltage at all times if that is what is needed.

Yes, corrosion on battery terminals or on ground connections to the frame and body will cause all kinds of strange things to occur. This is well known. Also, a battery that is not fully charged can create havoc as well. Keep in mind that an alternator is not for charging a battery; it is for maintaining a charged battery. In other words, if a battery is discharged, do not expect the alternator to completely charge the battery - one needs to use a dedicated battery charger.

As far as the transmission goes, what were the reasons for the 5 replacements?

If you had a bad PCM I would expect there would be communication Diagnostic Trouble Codes present, and that there would be multiple other problems or the engine just would not start.
 

·
Registered
Joined
·
207 Posts
Loss of battery power can case various kinds of problems, but ruining a PCM isn't one of them.

Five transmission replacement? And "strange things"? A fuller "story" would help people help you. (Including reporting error codes, if known, as chem_man said.
 

·
Registered
2003 chevy trailblazer_ltz
Joined
·
43 Posts
Discussion Starter · #6 ·
NOT AMMCO x5

1. 26,000 mi. It had a clunk in Drive and reverse the transmission was replaced tranny under warranty.
2. 148,000 mi Lost reverse
3. 161,860 mi. Internal fault, pan full of metal
4. 225,000 mi. Installed new shift cable. Transmission would not shift correctly. On the way to have the cable replaced the transmission light came on. I scanned it. I don't remember what code came up. I think it was something to do with the torque converter solenoid stuck open. Another transmission? I asked it they replaced the shift cable. He said it was fine.
5. Didn't even make it home (18mi) when car would not go at a stoplight. Fan clutch really loud. Again no info on shifting that i reported. does not shift to D1. Repair shop had it towed back to shop. I told them it didn't shift correctly Mechanic did not change some kind of fluid when replacing tranny. Warrantee voided. Mechanic replaced tranny. I made it home, drove it a few days later and it barely made it home again. The car does not feel like it shifts correctly.
I'm not even driving it. Mechanic doesn't respond.
I bought the car new. I've towed a 16ft tri hull boat with it. that's the heaviest thing i've towed. It had no trouble towing. Other than towing the boat it's been my every day car. I have most all problems and repairs noted with milage in my book.. It gives me grief if it even has a speck of corrosion on the battery terminals. ie: dumped a bunch of tranny fluid for no reason, completely locks up car in gear and can't get keys out of ignition, lights go crazy, radio changes stations and there's more I can't remember. All were "fixed by cleaning battery terminals.
I will try to find the post stating the car should have power at all times and share what it says.
 

·
Premium Member
2004 chevy trailblazer_lt
Joined
·
3,229 Posts
I'm going to assume that a GM dealer replaced the first transmission because it was under warranty as you stated.

My question is this - for replacements 2 - 5, did you use the same shop/mechanic?
 

·
Registered
Joined
·
207 Posts
Holycowitsreallyhardtoreadgiantblocksofcrammedtogethertextinabbreviatedinformationlikethat.

Your issues are not related to having power loss to the PCM - which doesn't mean that you don't have a PCM problem. Just that it's the wrong tree. Forget the transmission stuff for a while and say more about "the slightest bit of corrosion on the battery cables."
 

·
Registered
2003 chevy trailblazer_ltz
Joined
·
43 Posts
Discussion Starter · #9 ·
The dealership did the second transmission, 3rd was aamco(which lasted the longest), and 4th & 5th were replaced by a private transmission business. Do you think the shifting cable not working correctly could be causing the tabby to fail? Not much more to tell about the corrosion on the battery. How can I tell if the pcm is bad?
 

·
Registered
2003 chevy trailblazer_ltz
Joined
·
43 Posts
Discussion Starter · #11 ·
I'm going to assume that a GM dealer replaced the first transmission because it was under warranty as you stated.

My question is this - for replacements 2 - 5, did you use the same shop/mechanic?
NO NOT ALL THE SAME SHOP
#2 WAS ALSO UNDER WARRANTY
#3 AAMCO
#4 LOCAL MECHANIC
#5 SAME AS 4
 

·
Premium Member
2004 chevy trailblazer_lt
Joined
·
3,229 Posts
Thanks. I'll let our resident transmission experts comment on this information.
 
  • Like
Reactions: Ravalli Surfer
1 - 14 of 14 Posts
Top