I just bought a 1999 Grand Cherokee limited with 170k miles with the 4.7l engine. The over drive button will not turn off the over drive. I am getting one code which is p1698 which means Engine control Module (ECM) unable to communicate with Transmission Control Module (TCM). Before I go buy a new ecm or tcm I would like to trouble shoot this. The Jeep shifts fine. No problem there. Where should I start looking and how should I go about troubleshooting this. Thank you.

 

I believe there's a relay for the overdrive.. you might check into that

 

I know there is a fuse and it looked good. I changed the fuse and still the same problem. I checked all the fuses and they are all good. I went to a parts store to use their scanner. I asked about a relay or a switch and he said no not for my car.

 

So now my speedometer only works some of the time. Getting a p0500 code along with the tcm code. All the other gauges work fine including the tach. So I im guessing its either the ecm or tcm. Any ideas?

 

I disconnected and reconnected the tcm wire harness. Now the speedo works but still tcm code. Anyone?

 

I don't know why I keep updating whats going on. No one responds. Oh well. It turns out the overdrive does work but for some reason it will not light up on the dash. It will light up during its self test on startup. It is at the dealership now checking what is causing the code.

 

Its fixed. There was a pin not making contact with a connector. Dealership reseated the pin and it all works. Total cost $127. $115 for diagnostic and the rest for a rental. No charge to fix the pin.