WTECIII display shows “X” with mode light illum

[expeditionnw]

2000 M1079. Truck starts and runs great.
However, as soon as master switch is turned on, Trans controller displays “X”, and the mode light is illuminated. Diagnostic mode is inaccessible.

The controller is a known working unit.

It’s strange to not be able to access diagnostic mode, I am going to pin the plug next.

Any ideas?

 

[Ronmar]

What year truck? this is a WTEC3 controller.

This looks like it is missing something major for basic operation.

The system gets battery voltage all the time, and switched ignition power to activate. Are both these present(2 separate fuses/breakers).

Next would be to check interconnect cables. TCU(under pax dash) to controller in drivers dash, TCU thru bulkhead connector in the tunnel down to the transmission control module on the transmission passenger side...

 

[expeditionnw]

What year truck? this is a WTEC3 controller.

This looks like it is missing something major for basic operation.

The system gets battery voltage all the time, and switched ignition power to activate. Are both these present(2 separate fuses/breakers).

Next would be to check interconnect cables. TCU(under pax dash) to controller in drivers dash, TCU thru bulkhead connector in the tunnel down to the transmission control module on the transmission passenger side...

My edited post must not have shown up for you. When I first posted, it would not allow me to type, once I put the picture in. I had to go back and edit. Sorry.


It’s a 2000, yes, Tech three.

Had unplugged the TCM and checked for corrosion on the contacts before plugging it back in. No change.

 

[NDT]

X usually means “I am dead, send me to Transmissioninstruments.com”.

 

[Ronmar]

well if it won't even enter diag mode, it sounds as if the pushbutton controller and TCU are not communicating, so an issue with one or the other or the cables in between... i wonder if Allison doc or a scantool can talk to the TCU?

 

[expeditionnw]

X usually means “I am dead, send me to Transmissioninstruments.com”.

that was my thought also, however, I swapped in a brand, new controller and change nothing.

I also plugged that controller into a functioning truck and it works fine.

 

[Ronmar]

that was my thought also, however, I swapped in a brand, new controller and change nothing.

I also plugged that controller into a functioning truck and it works fine.

so TCU under the passenger dash or the wiring between the two?

 

[NDT]

If for sure the TCU is good, suggest you check out the VIM under the power panel for issues such as blown fuse.

 

[expeditionnw]

so TCU under the passenger dash or the wiring between the two?

I haven’t been tested the harness yet for continuity,

I’m going to quick swap in another TCM and see if that changes something.

 

[Ronmar]

If for sure the TCU is good, suggest you check out the VIM under the power panel for issues such as blown fuse.

No VIM on a wtec3, they separated the TCU from the controller on the 3 and put the TCU in that same place under the passenger dash… They moved the relay functions provided by the VIM up into the main power panel…