4l80e head scratcher.. need help

[Cluongo]

Initially the TCM gave me code 73 when I put it in diagnostic mode by jumping A and E on the 6 pin plug. Now, it does not throw any codes. I suspect that's because the TCM was unplugged.

 

[Cluongo]

You should be bypassing the TCM and using the snap on tool to act as the TCM, thus eliminating the transmission as the Culprit

Is this something a transmission shop would have? Or is that something the modus can do? Remember the only way I can read the tcm is through the obd1 port I wired up. I would imagine I can't do the normal things a modus could do with just that setup..

 

[Mogman]

I would definitely buy another TCM from ebay if I could find one cheap. The cheapest I've found are $600-$1000.

The TCM itself is the same as used in the civy vehicles, over 1000 for sale now on Flebay, again I would look for the hardware number as I showed in an example above to see if there are any with the same number first. (search for the number on your TCM, not the eprom)

 

[Cluongo]

Again what code/codes is the TCM throwing?

The tcm is not throwing any codes when using the modus.

 

[Mogman]

So if you drive it with the old TCM in it, it stays in limp mode and does not throw any codes when the pins are shorted together? I have no idea weather the modus is/can work properly with the setup you have and no ECM.

 

[Cluongo]

So if you drive it with the old TCM in it, it stays in limp mode and does not throw any codes when the pins are shorted together? I have no idea weather the modus is/can work properly with the setup you have and no ECM.

The only code it ever threw was 73 with the original TCM. That code is for the PCS (pressure control solenoid) circuit. Thats what led me to replace all of the internal solenoids and internal transmission harness. When that did not fix the issue, I found the troubleshooting manual online and began checking wiring. Couldn't find any issues there. Thats when I started looking at the TCM as a suspect.

 

[Mogman]

looking into this brings up the question about TCM compatibility, it would really help if some folks would give me the part number on their TCM itself so I can do more research.

 

[loosegravel]

What about the two external speed sensors. You mentioned replacing the internal harness and all of the internal sensors. Is there possibly a problem with the external speed sensors or the twisted pair wires to each?

 

[Mogman]

I am 100% wrong, yet almost right.
The most common 4L80E TCM, like 99.99% of them out there are not compatible, the same TCM was used on some early civi 4L80Es but they are scarcer than hens teeth.

 

[Cluongo]

I guess my next move would be to replace the speed sensors just to rule it out. If that doesn't make a difference I'll look into an aftermarket TCM and harness. I'll keep you guys posted.

 

[Dave2018]

This is the adapter I made to go from the 6pin cannon plug on the tcm housing to an OBD1 port.View attachment 896345

This is something that is important. If you wish to make up an extra and sell it I'm interested. Would be great to be able to have a regular shop connect. Just let me know if your interested. Dave 8325386328