2000 Nissan Sentra transmission issues- is the PCM/TCM toast?

This car I recently bought with a few minor issues but the transmission see med ok, shifted normally, had good power on acceleration, overdrive could b
e turned off and on, etc. Now the OD light won't come on, and the car seems to be pretty well stuck in limp mode. No matter what gear I select i won't downshift or upshift. Transmission fluid is pink and doesn't smell burned. I am able to connect an OBD reader to the port and read check engine codes which the only one I have is P1140 which I believe to be caused by a defec tive intake camshaft sensor which only really affects advancing the timing. I have tried in vain to get the OD light to respond to the button on the s ide of the gear selector. I have also tried getting the diagnostic mode to come on as detailed in the FSM but I have not had any success at all due to the fact that the OD light won't come on anymore. I know where the ECM is (passenger firewall) but I guess I am begging for help and experiences from others who have run into this issue. The fact that I can't get the OD ligh t on means there is a broken wire or a broken control module I am guessing? Just any advice please from people who I'm sure have more experience that I do. Thanks so much!
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