No Power to TCM Reason for No Shifting? - JeepForum.com
 
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post #1 of 6 Old 05-26-2020, 02:46 PM Thread Starter
riotgrrrrrl
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No Power to TCM Reason for No Shifting?

Hi all,

Returning again with some new info for an old problem stumping me. So...as background please reference this earlier thread I made: https://www.jeepforum.com/forum/f13/...fting-4395143/. TLDR: My Jeep is stuck in 3rd gear, the usual fixes of replacing the governor sensor/solenoid not working.

I had posted an update on the older forum with some new hints, but didn't get much response. I'm a pleb at this forum so I hope it is ok to start a new thread to get more input and visibility. Essentially, I tried replacing the transmission control module (TCM) thinking that might have got fried when my daytime running light module fried a long time ago. This also did nothing and I am still stuck in 3rd gear. I found some pin-out voltages for the TCM though on an older thread and started checking voltages (See the old post in the linked thread, but I also reproduced it below). I essentially found out that it was not getting its 12 V source on F16. From the wiring diagram (also in my update post in the linked thread and reproduced below) it seems like the wiring goes from the TCM, to the datalink connector, to the power distribution center (PDC). The fuses (3,6) are fine in the PDC, so where the heck is this break or disconnect? Could someone point me to where the ABS/TCM data-link connector is for a 1994 jeep grand cherokee? I know where the OBD1 L-shaped plug is in the engine compartment next to the power-train control module. Is this it? Is the TCM connected to the powertrain control module at all? Could that have got fried?





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post #2 of 6 Old 05-26-2020, 05:01 PM
jeepjeepster
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Its on the left side of the dash just in front of the 4wd lever. Pull the carpet back a bit and you should be able to see it.

1994 ZJ-I6 w/270,000 mi
1998 ZJ 5.9 w/66,000 mi Slate Black
2004 KJ w/108,000 mi
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post #3 of 6 Old 05-27-2020, 07:32 AM
LordHobbit
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Check those fuses again and then check to see if there is voltage on them. That will at least tell you there is power at the fuse.

93 red ZJ 196k 4.0. Spent more money than I should have ...
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post #4 of 6 Old 05-27-2020, 05:39 PM Thread Starter
riotgrrrrrl
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Quote:
Originally Posted by jeepjeepster View Post
Its on the left side of the dash just in front of the 4wd lever. Pull the carpet back a bit and you should be able to see it.
Awesome! I found that plug and tested for the voltage to the TCM on it as per this comment "You can verify +12v to the TCM on Pin#2 of the Data Link connector. Ground is on Pin#4." from this forum: https://www.jeepforum.com/forum/f13/...-mode-1450961/ and got a few hundred mV, not 12 V. So could this be from a bad PCM, or would a broken/bad circuit in my transmission pan potentially cause it?
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post #5 of 6 Old 05-27-2020, 07:42 PM
jeepjeepster
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To rule that out, you could unplug the TCM and see if you have 12v.

From looking at your drawing, the PCM has nothing to do with the 12v going to the TCM. Make 100% sure the fuse is getting 12v and it has 12v going out of it.

1994 ZJ-I6 w/270,000 mi
1998 ZJ 5.9 w/66,000 mi Slate Black
2004 KJ w/108,000 mi
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post #6 of 6 Old 05-28-2020, 07:09 AM
LordHobbit
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Correct, follow the 12V line and figure out where it is broken. May be as simple as bad connection/pin in a connector.

Or that nasty green death that plagues wiring ...

93 red ZJ 196k 4.0. Spent more money than I should have ...
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