Bad PCM. how hard to replace?
 

The dealership and my mechanic have informed me that my pcm is bad in my 03. this is no shocker to me. ive had my superstitions for the past couple years now. buying the pcm is not an issue, having the dealership reprogram my car is only $75 and not an issue either. What i want to know is: how hard it will be to replace it on my own? is it difficult to get to? is it in a sealed location that only the dealership should probably mess with? has anyone done this on their own before? im looking to save some $$ by replacing it myself then ill have AAA tow it (free towing) to the dealership to reprogram it. im hoping that replacing it not only fixes my ac problem, and coolant fan issues, but also my never-ending-going-on-4-years of abs bullcrap. I dont even know where the pcm is located...so i dont even know where to start.:o

Its n ur airbox. Phtsially easy to change :)

PCM failures are not common (they happen, but very seldom). If you don't mind my asking, what is the dealer feeling points to the PCM being faulty??

You mentioned ABS issues, those are commonly bad speed sensors. I'm not sure I've ever heard an A/C problem tied to the PCM (but I know some of the A/C controls go through the PCM). And the fans, what are they doing or not doing??

The dealership said they are 85% positive the pcm is bad. the other 15% he would lean towards a bad ground wire. The fans would turn on only after the engine was up at over 240, then they would not shut off until after it was below 185. it was overheating anytime the car sat for more than 8 minutes without a speed of more than 30mph airflow to cool her off. My ac would intermittently work. i could be driving down the highway and then all of the sudden it would work, or it would sometimes work as soon as i started the car. the dealership mechanic told me there was no communication coming from the dash cluster unit. i still have yet to replace that to see if its true, however i did rip one out of a junk yard and plug it in to see if it would work and it did not. I assumed it was bad, or the unit itself was in fact not bad to begin with in my car.
When it comes to abs, i know lots of ppl with montes and impalas that have abs issues. stupid hubs going bad, wire harness becoming faulty, ground wires falling off ect ect. i had all of my stuff replace to solve the issue, but within 3 days of driving the damn lights all came back on. every time i would take my car to my mechanic the computer would read something else was wrong with the car (and this was within a matter of a cpl of months and me not even replacing anything) last time i had him check it he said the only thing it was bringing up was the abs pump itself was bad. im not paying over $900 to replace that and he said he has never replaced one before so its unfamiliar to him. dating back a few years ago i had ideas and feelings the my pcm was bad with all the weird stuff happening. had my whole theory wrote down and everything was connected, and even the dealership said that my theory was 50% possible. since then i had to rebuild trany, replace my whole front end, half my rear end, and tear my engine down 2x to replace intake gaskets, and then intake and head the 2nd time. now the overheating issue with no sign of any coolant leaks anywhere. so we put in a toggle switch so i can manual control my fans.

thanks :) at least i know where to begin. i plan on having this fixed with my government funded savings account (income tax return lol) which will be within the next cpl weeks. i pray this will fix the multiple issues because out of the 4 1/2 years of owning this car i only had 1 good year and the rest have been full of problems.

When it comes to the temp of when the fans come on and off, is that temp reading coming from a scan tool connected to the ODB-II diag port (so it's a true sensor read) or is it from the cluster? The reason for this is that I've seen a cluster fail and temp gauge read one thing, but the sensor data in the PCM does another.
As for the A/C, did anyone check how full your freon is? If you are right on the border, it's possible that is why it won't always activate. The system will not run if it's low on freon (it's a safety).

This is my opinion, take as you wish, but you would have to walk down a diagnostic for each one. The PCM is rarely the problem (so I am always skeptic of it). But there are times that it is the issue.

To my knowledge, your PCM must have your VIN programmed into it and you may have to perform a "security relearn" for it to work.

the temp readings came from an actual scanner after my i noticed my gauge was way over the limit several times while stuck in Boston traffic. the mechanic there said its usually due to air getting into the intake but there was no leaks found. my freon is completely full. thats the first thing i thought of and had checked. all my ac stuff is new as well. My mechanic has been right about things 95% of the time so just to be safe thats when i took it to the dealership to get their opinion and they said the same thing. so i have 2 mechanics telling me my pcm is bad and they are both 75-85% sure of it. ive had a gut feeling for the past cpl years its been bad, but like you said...they rarely go bad so i was blowing it off as over worrying. all i want to do is take the time to swap it out. i plan on having the car towed to the dealership to be reprogrammed once its in. ive never replaced one. ive torn a few engines the whole way down...but have never messed with a pcm

why don't you take the opportunity to get a tuned pcm from a vendor? doesn't even have to be a wild tune just a few tweaks like fan turn on temp.

btw what engine do you have?

X2. Repair needs are always a good excuse to upgrade :) Thats a lot of custom stuff was justified on my car :)

the engine is a 3.1....and up until today i was still planning on buying a new ecm (not called pcm anymore?) at auto zone for $150. pay dealership $75 to program it and be done. BUT the car has decided she didnt want that done and i lost cylinder number 5 today so my engine is now toast. my new route is to figure out if im replacing her, rebuilding the engine, or just dropping a *unknown-of-care* used engine in her