Transmission electronics wiring diagram
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Joined: May 2025
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I got around to step #5 this evening, and the transmission worked fine, so I think I have a bad PCM.
As an aside, several of the tips I saw on the internet suggested to scrape back the coating on the pink wire (pin 30) of the PCM connector to be able to connect it to ground. I chose another method... Pin 30 connects to pin #2 of the transmission relay. I pulled the relay, wedged a wire into its contact receptacle, and then re-installed the relay. I then ohm'ed out the connection between the wire and pin 30 at the PCM harness to verify good contact was made. I then grounded this wire.
I started the truck up (did not bother to clear the codes), put in in Drive, and drove away (in 1st gear). The transmission then shifted normally through all gears up to and including overdrive. Nice.
It looks like the next step is to buy a new/used PCM computer. What a shame. For those electronics geeks out there... I am almost certain that the PCM computer has an Open Collector or Open Drain output circuit that is used to 'connect' pin 30 to ground to activate the relay. Open collector ICs are about $0.20. A rebuilt PCM is about $250.00.
As an aside, several of the tips I saw on the internet suggested to scrape back the coating on the pink wire (pin 30) of the PCM connector to be able to connect it to ground. I chose another method... Pin 30 connects to pin #2 of the transmission relay. I pulled the relay, wedged a wire into its contact receptacle, and then re-installed the relay. I then ohm'ed out the connection between the wire and pin 30 at the PCM harness to verify good contact was made. I then grounded this wire.
I started the truck up (did not bother to clear the codes), put in in Drive, and drove away (in 1st gear). The transmission then shifted normally through all gears up to and including overdrive. Nice.
It looks like the next step is to buy a new/used PCM computer. What a shame. For those electronics geeks out there... I am almost certain that the PCM computer has an Open Collector or Open Drain output circuit that is used to 'connect' pin 30 to ground to activate the relay. Open collector ICs are about $0.20. A rebuilt PCM is about $250.00.
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From: Clayton MI
15 year old thread...... are any of the participants even still here?
What do you mean by 'starts sluggish'? Is it trying to start in 2nd gear? Is the engine hard to start? Is the trans slipping?? What's going on??
What do you mean by 'starts sluggish'? Is it trying to start in 2nd gear? Is the engine hard to start? Is the trans slipping?? What's going on??
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It starts like on second gear and it has a hard time to start in the morning or if parked for a long time. Once it gets past 10 miles it works fine until I stop and it starts off the same way. Every once in a while if I stop or start it the problem is not there. So I think it is some sort of bad connection. Which is why I wanted to know if it needs a ground added. Thanks in advance
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It is something that I just have parked and work on it when I remember. I will take a look at any codes and see what it can be. Could grounding the pink wire hurt it at all? Thanks for replying.
