jimmydean

I just bought an 05 Cobalt with the 2.2, automatic, 124k miles. I never heard it run, the guy I bought it from told me it had a TCM issue. Had it towed to my mechanic and he tried grounding the TCM to the body like everyone suggests, but the car will only run for about 8 seconds before shutting off.

There are no codes coming up for the engine or trans. The tcm is very hot to the touch.

When he unplugs the tcm, the security light comes on. When he unplugged the fuse for the ecm/tcm, the car ran for 3 minutes but ran like crap, then stalled out.

Can the tcm being bad cause the security system to come on?

I wanted to buy a used tcm but I've read it needs to be programmed by the dealer. I called my local chevy stealership and they said they have about a 30% success rate of reprogramming used tcm modules. It's like $95 per reprogram, so I don't want to go this route if it's not going to work. Can the dealer TEST my current tcm to see if it's bad... not going to tow it there, but if I bring them the module?

My mechanic found a company that make a security bypass module for the Cobalt and other cars for $179, but I'm not sure if this will solve my problems. The tcm is very hot to the touch, so obviously something is going on there. Assuming the security bypass works, who knows what problems I'll have with the tcm... I've never even driven the car so I don't know what to expect.

Any input or suggestions on this?

jimmydean

bump... anyone??? i've heard this was a really common issue with these cars, i was hoping to get some feedback on this

jimmydean

any other good cobalt forums out there? i really need to get this figured out...

dsmnutz

There is no way for the dealer to test the module by itself. Sounds like it could be a wiring issue...or tcm internally shorted. Probably would have been better off towing to dealer than your 'mechanic'.

jimmydean

thanks for the reply. going to order a used tcm and try that route. the numbers on mine are 24268631284... do the last 4 numbers matter? can't seem to find any with the complete numbers matching(none on ebay, car-part.com, or even in a google search), but many with the first 7 digits matching. i am guessing the last 4 digits don't need to be matched up but would like some type of confirmation.

dsmnutz

I would buy one from dealer if I were you. They are going to have to program it anyway, unless your 'mechanic' has a tech 2 or mdi as well as access to tis2web...being a 'stealership' technician as you say, I have alot of experience with module replacement and programming.

jimmydean

i dont want to spend whatever it costs for a new one! how much are they... $$400? $600? come on... just want to get this done as cheap as possible. i'm sure you can understand where i am coming from.

DC02

I say buy the new one. If it is that hot there is a clear issue, it will throw the security light since it is (I believe) used for a major communication port for much of the ECU data.

$400 for a new one vs. chasing it with old parts.... You do the math.

turbosmart4

iTrader: (18)

Buy a new one..... Cheapest route is not always the best....

jimmydean

my mechanic installed the used TCM, all codes are gone now, but the car is still turning on for 2 seconds and shutting right off, security light is coming on. this is what it was doing before, even with the original TCM. but, all the codes are GONE from the TCM. so, my question now is this... does a used TCM cause the car to go into security mode if it isn't reprogrammed to the car? because if it doesn't, then i am going to buy this and bypass the security system altogether: NEWROCKIES Inc | Bypass, disable and remove VATS, PASSKey and Passlock Security Systems in GM cars

so basically, i need to know what the typical reaction is to a used TCM being installed on the car without it being reprogrammed. does this trip the security system or would it just run/shift poorly?

dsmnutz

You should have bought the new module and had it programmed at the dealer. Modules that use class 2 data link communication look for whats called a SOH or state of health message. An incorrect VIN number programmed in one of these modules will cause the PCM to recieve an invalid SOH message, triggering the VTD or vehicle theft deterrent system. The VTD shuts off the fuel pump, which is why your car runs for a few seconds and shuts off. A VTD relearn procedure is part of the programming procedure. BTW, we charge one hour labor for programming, which is cheaper than that bs bypass kit you mentioned. Your 'mechanic' obviously doesn't know GM vehicles and is in over his head.

jimmydean

thanks for the continual smart ass remarks. a simple "yes, the security system is triggered because of the non programmed module" would have been sufficient. i love how you keep putting mechanic in quotes to insinuate he's inferior to you... real classy.

jimmydean

I don't need the car back fast, I need to get it repaired cheaply. I am a used car dealer... can't afford to make a profit when you pay 3x the labor at the dealer. If it was my own car and I didn't know a thing about cars, I might take my car to the dealership then. Even then, I don't like overpaying for anything and always seek out the best deals, that's just my nature. Sometimes you have to bite the bullet though and take your car to the dealer for an issue like this, but if you don't try to save some money first then you're a sucker in my opinion.

dsmnutz

I was trying to make the point that you could have had it fixed already. I wasnt trying to say im superior to anyone, some things are next to impossible without the equipment we have at the dealership...

dsmnutz

You could try finding someone local that has a mdi or tech 2 and access to tis2web, someone that works at a dealer, maybe a friend of a friend, or maybe even run a craigslist ad for someone to do it on the side and save a few bucks...again wasnt trying to **** you off, just know how expensive throwing parts at one can get.

DC02

I feel reminded of why I don't like buying used cars now either....

A computer issue on a newer type car is almost always going to be a dealer item. Unless you have a friend or a friend of a friend that works at a dealer and has the equipment to do it for you on the side, you're almost always better off fixing it that way. Since you found the issue, doing a reflash of that TCM for that car should be a fairly simple process since you know exactly what you need.

I do agree, going to a dealer on a blind whim sucks and I would never do it as a first step. But IF I can figure out the issue first and know what has to be done to fix it and a dealer is the fastest/best qualified option, then I'm going that route.

Mechanical stuff = mechanic.

Computer stuff = dealer

Cobalts&Peaveys

I really think he wasn't being a smart ass, just trying to share the brutal truth of it. The more systems get integrated, the more I want to learn how to do them myself. I would like to know however. My cars shift cable was disconnected and pushed out of the way for someone who was just too lazy to walk around it to load tires. The car was already in the process of having other work and waiting for parts. The linkage was reconnected. I'm getting no codes no heat issues, and the car won't start because of the other issues. If the TCM needs this relearn procedure, how would I know. I'm not locked out of the car in any way shape or form. Would this very minute linkage issue cause me to have to relearn? The car ran for 30 minutes without issue before I shut it down and locked it up so I could focus on the other issues. Considering the 30% success rate, which worries me far more than the cost. I do not want to security bypass anything. That is a absolute last resort.