I came across this over on JF a couple years back, Ive posted it several times but it doesnt seem to catch on. If your PCM is already a paperweight why not give this a shot, you have nothing to lose? This came from a guy in Electrical and Computer Engineering...Granted--this is for a no start issue but it looks like it shows what to look for when something goes wrong within the PCM. I have no idea if it would be the same or not regarding the transmission issues but it would be nice to see someone take theirs apart and post pics. See below:
SUCCESS!
I found the problem - and it is in the PCM. What follows is how to fix it.
Symptoms: No fuel or volt meter when you initially turn the key on. Will not start. After several cycles of the key - or just leaving the key on for a few seconds - it will start right up after turning the key to off and immediately starting it. Runs fine otherwise.
I spoke with a co-worker last night about it (remember, I work in the Electrical and Computer Engineering Dept) and he said without hesitation, "Automotive computer problems are always capacitors. The computers are built like tanks, so open it up and look at the caps."
That's just what I did. Three plugs on the PCM and three bolts holding it to the firewall is all that's needed to take it off. The PCM is a clamshell style case with an aluminum divider that fits in the middle. Remove the Torx screws and use a couple of screw drivers to pry the case open. Don't put the screw driver in any more than just past the edge though - there's electrical components inside you don't want to screw up. Once the seal is broken all around, grunt, then open that puppy up like a book. Don't worry - all the circuits are on flexible material - you won't hurt it from opening the case.
The PCM once it is spread open and the inner aluminum block is removed.
What we're looking for are the capacitors. They look like tiny little soda cans. They are under the metal clamps shown here to isolate out any vibrations from the road.
Wait... what are those dark spots on the board where the capacitors are soldered on? That's the electrolyte from the capacitor that's leaked onto the circuit. Let's break out the USB microscope and take a look up close.
Those capacitors have obviously failed and leaked electrolyte onto the circuit. For reference, this is what a new capacitor looks like. The proper replacements are 220uf 25v. Very cheap parts - like $5 for 15 cheap.
I unclipped the capacitor mounts by prying with a finger to distort the clip so I could get a tiny screwdriver in there to open it.
Sorry there are no more progress photos, I kinda got focused from here on out. I didn't trust myself to desolder the capacitors from the board and resolder in place so I simply snipped the existing leads close to the capacitor, laid the new capacitors in place and soldered the new leads to the old leads. I would have called up a co-worker, but it's a Sunday morning during the holiday break. If nothing else, I can take it in to have it professionally soldered now that I know it was the problem. I'm not an electrical engineer - I just work there
After putting it all back together the Jeep fires up on the first try every time and has no issues on the road. Took me about 45 minutes from start to finish.
I'm fairly certain this is the fix to the problem, but I won't be able to say for sure until tomorrow morning when I try and start it after sitting overnight.
SUCCESS!
I found the problem - and it is in the PCM. What follows is how to fix it.
Symptoms: No fuel or volt meter when you initially turn the key on. Will not start. After several cycles of the key - or just leaving the key on for a few seconds - it will start right up after turning the key to off and immediately starting it. Runs fine otherwise.
I spoke with a co-worker last night about it (remember, I work in the Electrical and Computer Engineering Dept) and he said without hesitation, "Automotive computer problems are always capacitors. The computers are built like tanks, so open it up and look at the caps."
That's just what I did. Three plugs on the PCM and three bolts holding it to the firewall is all that's needed to take it off. The PCM is a clamshell style case with an aluminum divider that fits in the middle. Remove the Torx screws and use a couple of screw drivers to pry the case open. Don't put the screw driver in any more than just past the edge though - there's electrical components inside you don't want to screw up. Once the seal is broken all around, grunt, then open that puppy up like a book. Don't worry - all the circuits are on flexible material - you won't hurt it from opening the case.
The PCM once it is spread open and the inner aluminum block is removed.
What we're looking for are the capacitors. They look like tiny little soda cans. They are under the metal clamps shown here to isolate out any vibrations from the road.
Wait... what are those dark spots on the board where the capacitors are soldered on? That's the electrolyte from the capacitor that's leaked onto the circuit. Let's break out the USB microscope and take a look up close.
Those capacitors have obviously failed and leaked electrolyte onto the circuit. For reference, this is what a new capacitor looks like. The proper replacements are 220uf 25v. Very cheap parts - like $5 for 15 cheap.
I unclipped the capacitor mounts by prying with a finger to distort the clip so I could get a tiny screwdriver in there to open it.
Sorry there are no more progress photos, I kinda got focused from here on out. I didn't trust myself to desolder the capacitors from the board and resolder in place so I simply snipped the existing leads close to the capacitor, laid the new capacitors in place and soldered the new leads to the old leads. I would have called up a co-worker, but it's a Sunday morning during the holiday break. If nothing else, I can take it in to have it professionally soldered now that I know it was the problem. I'm not an electrical engineer - I just work there
After putting it all back together the Jeep fires up on the first try every time and has no issues on the road. Took me about 45 minutes from start to finish.
I'm fairly certain this is the fix to the problem, but I won't be able to say for sure until tomorrow morning when I try and start it after sitting overnight.
