6.5TD Codes / Not shifting

[pnwestern]

Hey all, picked up an automatic 92’ 2500 with the 6.5TD/4L80E a month ago after it sat untouched for 3 years (PO, a family friend, unfortunately passed). Ran and shifted great when I picked it up.. he took great care of this rig. I’m an 80s/90s euro car guy so new world but couldn’t pass it up when the family offered it for a good price

Anyways, 1 week ago I was getting off freeway and suddenly the truck won’t shift and tops around 45mph (redline). Codes it’s throwing:

22 - TPS Signal Low
28 - Trans pressure switch error
59 - Trans fluid temp sensor circuit error
85 - PROM error
87 - EPROM error (flash memory error)

Watched videos and tested TPS prior to codes, seemed to read 7-12 so way high but I feel I’m doing it correctly. Now seeing the other codes I feel it could be TCM? Thoughts and advice?

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[pressureangle]

First, verify the powertrain system grounds- Black/white and Tan/white on the passenger side engine block (manifold stud on mine) rear by the firewall. PCM, TPS, and trans temp all share those grounds.

 

[Schurkey]

Hey all, recently picked up an automatic 92’ 2500 with the 6.5TD/4L80E a month ago after it sat untouched for 3 years when the PO, a family friend, unfortunately passed. Ran shifted great when I picked it up - he took great care of this rig. I’m an 80/90s euro car guy so new world but couldn’t pass it up when the family offered a good price

Anyways, 1 week ago I was getting off freeway and suddenly the truck won’t shift and tops around 45mph (redline). Codes it’s throwing:

22 - TPS Signal Low
28 - Trans pressure switch error
59 - Trans fluid temp sensor circuit error
85 - PROM error
87 - EPROM error (flash memory error)

Clear the codes, see what comes back.

Watched videos and tested TPS prior to codes, seemed to read 7-12 so way high

7--12??? Volts? Percent? Something else?

Does the reading increase and decrease smoothly as you push and release the pedal?

Now seeing the other codes I feel it could be TCM?

I'm not familiar with Diesels. Does your vehicle even have a TCM?

 

[ChRoNo16]

My brother had a 96 with the 6.5TD and I believe he had issues with the electrical connection at the trans, he had to replace the pins as they has corroded out

 

[pressureangle]

I'm not familiar with Diesels. Does your vehicle even have a TCM?

The diesels have a TCM to '93 and a PCM from '94 on when they got the electronic fuel pumps. Located behind the glovebox per usual, nothing is the same as the gas motor in harness or box. PCM models are fly-by-wire with the TPS on the pedal.

 

[Schurkey]

The diesels have a TCM to '93 and a PCM from '94 on when they got the electronic fuel pumps. Located behind the glovebox per usual, nothing is the same as the gas motor in harness or box.

Since this is a '92, and doesn't have a PCM...would it have a PROM or EPROM? Kinda wondering if Codes 85 'n' 87 are false.

 

[pressureangle]

Kinda wondering if Codes 85 'n' 87 are false.

In my factory '94 diesel supplement, codes 83-87 are completely absent. I got nothin'. The only mechanical I had was a '85 with TH400.

 

[pnwestern]

Thanks everyone. I had checked those grounds and visually they looked great, someone had already put a new terminal on but hearing that ground relates to all will have me swap a new terminal on and trace back (at least without removing too much). While under I did notice the trans connection had some build up, nothing too wild but was not clean by any means so will pull that off and clean it up/test continuity.

Also will retest TPS one more time and report back voltage. At the moment I can't recall exact voltage from which wires as I had tested in a variety of pairs

 

[pnwestern]

Update - Still no shifting. TPS verified good. 5v and ranges from .7 with a steady climb as throttle opens. Tested ground at back of intake and was good but replaced anyways as well as cleaned the wiring connection at trans. One thing to add is reverse seems to be tight as well.. needs a little more throttle and doesn’t free roll (similar to what you’d feel with a little parking brake on)

 

[pnwestern]

Also adding that I didn’t clear codes today but the day this started I did reset it so all codes are pretty fresh from just a few short drives