From google AI:
Yes, based on the multiple concurrent symptoms, it is highly likely that the PCM (Powertrain Control Module) is bad. The fact that you have no voltage reference to the TPS, no tachometer, the OD light is on, and the OBD1 code reader cannot communicate with the computer all point towards a central failure in the PCM or its main power/ground supply.
Sited evidence:
No 5-Volt Reference Voltage to the TPS: The PCM is responsible for supplying a consistent 5-volt reference signal to sensors like the TPS. The extremely low readings (<0.2V) you are getting, even after confirming good continuity in the wiring from the TPS to the PCM, indicate the PCM is not outputting the correct voltage.
No Communication with the OBD1 Reader: The inability of the diagnostic tool to communicate with the computer is a classic sign of internal PCM failure or a loss of power/ground to the module itself.
Multiple Unrelated System Failures: The PCM controls both engine and transmission functions (engine timing, fuel injection, shift points, etc.). Failures across multiple systems at once (tachometer, overdrive light, TPS, diagnostics) strongly suggest a core computer problem rather than separate individual sensor or wiring issues.
Flashing Overdrive (OD) Light and No Tach: These symptoms are often related to transmission control issues, which are managed by the PCM.
Just wanted to see what AI said. Search here might be more reliable information.
