Bad PCM/ECU?

GM has figured out yet another way to separate you from your money and that is by building computers that will not work in any other vehicle. You must buy a replacement from the dealer and have it programmed to your car. Got'cha! They started this nonsense with the 2002 models.

Also, you should be aware that when a mechanic has a scanner connected to your truck, he has the choice to press the "lock" button. You will never know that was done but it ties every computer on the truck electrically to the Body Computer which, to prevent you from replacing it, is built into the radio. No clue how this benefits the owner but it is a real good deal for GM. Once that is done, they can not be unlocked. If the high-failure radio needs to be replaced, you must also replace every other computer on the truck. Imagine, a truck that is not worth repair because the radio failed. This is just one of many reasons GM has lost so many of their repeat customers.

The safest thing you can do is to reinstall your old computer and take it to the dealer so they are responsible for anything that stops working. Most likely no one ever locked the computers so all you will need is the one Engine Computer, but I would have them do the diagnostic tests first and come up with their own conclusion. There are a number of more common things that cause stalling. In particular, GM fuel pumps often quit while they are running leaving you stranded somewhere. Many other brands fail to start up but once they are running, they continue to do so until the engine is stopped.

Did you do a Passlock relearn?


Thirty minute re-learn procedure:
1. Turn "on" the ignition, with the engine "off".
2. Attempt to start the engine, then release the key to "on" (vehicle will not start).
3. Observe the security telltale, after approximately ten minutes the telltale will turn "off".
4. Turn "off" the ignition, and wait 5 seconds.
5. Repeat steps 1 through 4 two more times for a total of 3 cycles/30 minutes ( the vehicle is now ready to relearn the Pass-lock™ Sensor Data Code and/or passwords on the next ignition switch transition from off to crank).
Important
The vehicle learns the Passlock™ Sensor Data Code and/or password on the next ignition switch transition from off to crank. You must turn the ignition off before attempting to start the vehicle.
6. Start the engine (the vehicle has now learned the Passlock™ Sensor Data Code and/or password).
7. With a scan tool, clear any DTCs if desired (history DTCs will self clear after one hundred ignition cycles).

Wrenchtech,
No, I have not done a pass-lock relearn (did not even know it existed) but will give it a shot. Thanks.

Caradiodoc,
Agree with your assessment of the car mfg "gotcha's". I had no idea they could or would lock all the computers together. Guess I am just a naive old man.

Thanks to both for your replies.

Ralph

The VIN numberis part of the programming for most modules in most vehicles these days.

You are not a naive old man. We expect manufacturers to have our best interest at heart and work to earn our repeat business. I worked for two TV repair shops many years ago. One fellow's motto was he had had to rip off the customer as much as possible the first time because they were not coming back a second time. He went out-of-business for lack of customers in an extended community of well over 100,000 people. That is the business practice of GM and Volkswagen.

My cousin made a nice living for him, his sister, and me on weekends in his tiny repair shop in a farming community of 2,000 people. He never had to advertise. All of his work came from word-of-mouth. He only quit business after thirty years because of failing eye sight and increasing taxes.

As far as locking the computers, we were warned about that numerous times by a very high-level Carquest trainer who ran into that on more than one occasion. In at least one of those the car was still under warranty so GM got to eat that one. We were told more than thirty computer modules were replaced and it took two days to install the software into them one at a time. With a second one, he did not know what the final outcome was after the customer towed it back home. This instructor owns a shop that specializes in driveability problems that no one else can figure out. Most of his customers are other shops. He is part of a network of similar shops and instructors all over the country and they are in constant contact with the engineers at the manufacturers. That is how we know we can believe what he tells us.

My biggest problem is I cannot remember everything he says because I miss so much while I am feverishly writing notes. In your case, I am very interested to hear why the salvage yard asked about the serial number. That implies Wrenchtech's procedure for simply programming the Pass-lock code is all that is needed. In spite of my sarcasm and disgust, I will be very happy to learn if that works. I have enough disdain for all of the unnecessary, unreliable computers on cars already. One less thing to be miffed over will not change that but it will sure be better for the owners.

I cannot tell you if the relearn is the only problem, but I can positively tell you that it will not run until the relearn is done.

Put the ECM in from the salvage yard and did the relearn procedure yesterday and the truck started right up. Now a few days of driving will tell if the ECM fixed the original problem.
I really appreciate the help. If it were not for Wrenchtech's relearn procedure I would be tearing my hair out (what there is left) and spending more money. Thanks Wrenchtech.
Regarding why the salvage yard was interested in serial numbers. He said that certain serial numbers will work as a replacement without having to be re-flashed (which costs about $150.00 here, outside Atlanta, GA. So, I gave him the serial number, VIN number and all the information about the vehicle so he could match them.
Thanks again.

Glad to hear it worked out for you.

Me too. Going to have to add that to my internal memory.

As a side note, I visited about a dozen Pull-A-Part salvage yards a couple of years ago including three in Atlanta. Met a lot of friendly people down there all over the place.

Latest and hopefully last feedback on this issue. The truck is and has been running fine the last four days, so I am assuming changing the ECM and relearning the pass-lock procedure fixed the problem. Thanks again for the help, could not have done it without help.

Ralph

Hi everyone, I have been searching the internet for help with my 2005 Colorado and this is the only site that I can see is legit! and even close to what I am going through with my truck. Okay, a few days ago my 2005 Colorado 3.5 liter just quit running on me in my driveway. Went to restart and nothing waited five minutes started right up. Engine light on I scanned it with obd2 got a code back po601 PCM, ECU failure? So I found on eBay a store that you send your VIN number they flash the used ECU send it to you plug it in and do the pass-lock and fire right up for $150.00 I guess I am asking for some help on what I should do? Is it worth it? After reading rwilley1 posts and what he went through makes me more comfortable doing this. Maybe I just answered my own question, haha! Thanks guys.

Hello,

Thanks for the compliment we do try to be a step above. Yes, it does sounds like you have a computer problem and I would go ahead and try the PCM you found on Ebay.

I would clear the codes and see if the car does it again first it could have been a voltage serge or a glitch.

Please let us know what happens.

Cheers, Ken

Thank you Ken for the advice I appreciate it! Okay, yes I will get the PCM/ECU and keep you updated.

Please let us know what happens.

Cheers, Ken

Hi everyone, I just got the new PCM from a reliable store on eBay. I emailed him my VIN number all the information he needed. Anyway I did the pass-lock procedure as instructed and motor did not start? So I disconnect the battery for twenty minutes. Now I am trying the pass-lock again. Now the pass-lock light on the dash is off? I am on the fourth time on trying to start the motor. I am at a loss here. Ia m going to try this a few more times then disconnect the battery for twenty minutes and try it again. I am thinking I might try to unplug the stock stereo as maybe something could be blocking the pass-lock procedure from working, just a thought. Anything will help, thanks.

If the security light is not flashing the pass lock is okay. Do you have spark and fuel pressure?

Here is a guide to help:

https://www.2carpros.com/articles/car-cranks-but-wont-start

Please let us know what happens.

Cheers, Ken

I am not sure? What is the easiest way to check for spark and fuel?

It is getting spark and tested for fuel, it is getting both. Anyway after we pulled the spark plug and put everything back together we tried to fire up the motor it started but it was missing bad. We let it run for about ten minutes then it just shut off?

Lets pull all of the spark plugs out to see if one looks different than the rest and lets do a compression test.

https://www.2carpros.com/articles/how-to-test-engine-compression

Look for one low cylinder.

Please let us know what happens.

Cheers, Ken

Hey Ken thanks for your help by far the best online mechanics I have seen and chatted with. Thanks guys. Okay, here is what is going on and updated. About a week ago my 2005 Colorado quit running on me so I scanned it got a code back po601. But otherwise the truck started and motor ran drove excellent. So I got a newer PCM on eBay they just needed the VIN number to flash got it Friday. I disconnected battery and removed old PCM and installed the new one. I did the thirty minutes relearn and motor never started? So I disconnect the battery for thirty minutes and the pass-lock dash light was off? Tried to start and nothing. I talked to Ken asked if engine was getting spark and gas. Yes it is I put the coil and plug back and motor back together went to start motor fired up but had a huge miss?

Turned off and let sit went to start and nothing. I got it to start maybe four times ran badly. Today Saturday put old PCM back in fired right up and ran like a champ! But then shut off five minutes later and got a code po601. Let the truck sit for two minutes then fired right up and I let it sit and idle for about twenty five minutes turned off came in the house for the night. Very confusing, haha! Okay, thanks again.

Oh man, it sounds like you have a bad flash or bad replacement computer. It is rare but it happens.

Okay, yeah, that is what I was thinking. I will get a hold of the seller and send it back for another or re-flash. I will keep you updated. Thanks again Ken.

Okay Ken, here is the latest update on my truck. I been through three PCM's first two did the relearn and motor would miss got the third PCM did the relearn and motor fired up ran good no miss but engine light was on and dash said oil change and reduced power. After fifteen minutes motor started missing. We checked for codes and got po107, po123, and po315. We tried to delete the codes and would not go away. Seller told me to check for bad sensors and I cannot do the idle relearn until all codes are off. I figured I would try new sensors anyway and hope for the best. So I went ahead and got a new map and crank shaft position sensor put them in today started motor ran fine but engine light and codes still there after fifteen minutes motor started missing. Tried to disconnect battery for twenty minutes put battery cables back on codes still there. Tried to delete and no still there. I emailed the seller I should say has been very helpful and willing to help. I have not heard back from him. More then likely probably wants me send this PCM back and he will send me another. But I have a feeling I am going to go through the same thing as I went through the first three times. I am at a loss here. I do not have the money to send to a shop trying to do this on my own with my good friend who is a mechanic. We are both at a loss. Okay, thanks guys.

This one looks like it is going to be tough. I think at this point we should do some wiring checks. Here is a guide and the engine /computer wiring diagrams so you can test for power grounds and continuity:

https://www.2carpros.com/articles/how-to-check-wiring

It could be the powertrain control relay as well.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Please let us know what you find.

Cheers, Ken

Hey thanks Ken for the information, I will take a look. I have to ask you can I take my original PCM in to a dealer and have them test it for codes like po601? I know code means faulty PCM, but can they rebuild it and flash it and how much? I am going on the fourth PCM from the seller and only one worked motor start, but fifteen minutes started missing. He is sending me out another PCM I have a feeling I will go through the same things like before. Also, do all the codes need to be gone before I do the crank cam relearn? Or the two codes that mean PCM needs to be relearned to crank okay? Also, can a good shop scanner do the crank and idle relearn? Sorry for all the questions but I know I will get the right answers from you. I tried asking the seller but he is not clear with me. Thanks ken.

Hey Ken here is the latest update on my truck. I got the fourth PCM did the relearn and motor ran great for about ten to fifteen minutes then miss. So I called are local shop and the mechanic did the crank and cam correlation he charged $50.00 for a five minute job but that is okay. mechanic called me about an hour later said my truck was ready. I picked it up drove it about forty miles went to a friends house turned motor off and visited for about fifteen minutes went to start the truck and fired right up then shut off. I started back up and engine light was on so I drove home and checked codes I got a po0014. I cleared the code and never came back. Since then I have driven my truck about four hundred miles and it runs great! Thanks ken for all the great advice!

Sometimes it takes a bit for the computer to fully relearn the engine.

Glad you could get it fixed, that kind of problem can be tough. Please use 2CarPros anytime we are here to help
.
Cheers, Ken

I had the exact same problem with my 2005 Chevy Colorado Z71. It would unexpectedly give me the Traction Fault and then "reduced power" announcement and then just shut off. It would restart most time a few minutes later, sometimes longer though. I was getting the P0601 OBDII code, internal memory problem with PCM/ECU. I ordered a PCM from eBay and replaced it. I went through the relearn process and it started on the third time and runs good. I am however getting a new code which is P0315 /Crankshaft Position not learned. I read where GM designed that to happen, so you have to get that one done with a Tech2 Scan tool. It does not affect how it runs but I heard it won't run as efficient, so I made an appointment to have it done at a local Chevrolet dealership. They said it will cost $135.00 plus tax. I only paid about $145.00 for the PCM, so it is a bummer I have to almost spend as much for that one code. Overall though, still much cheaper than it would have been if I had it all done at a dealership. By the way, I had to change the PCM about seven years ago as well, but I think it was for a different reason. It looks like it lasts about six or seven years each go!

Great addition to this thread and fix! Please feel free to help out whenever you are on the site. :)

Cheers, Ken

I ended up finding a local garage with a tech 2 scanner. They did it while I waited and only charged $70.00. That is about half the cost of the dealership.

Nice work and great information, the reprogramming is getting cheaper as it becomes more mainstream.