I've been having problems with codes that keep popping in spite of the fact that I have changed all the sensors, checked connections, wiring, grounds, etc...

Code DTC P0643 SENSOR POWER SUPPLY - ECM detects a voltage of power source for sensor is excessively low or high. When the malfunction is detected, ECM enters fail-safe mode and the MIL lights up (the car goes limp and will not accelerate beyond 2000 RPM). ECM stops the electric throttle control actuator control, throttle valve is maintained at a fixed opening (approx. 5 degrees) by the return spring.

This code pops as a result of several sensors not working as intended. The sensors affected are : Accelerator position pedal sensor (1 and 2), refrigerant pressure sensor, power steering position sensor, EVAP control system (pressure sensor, control valve). Evap purge control valve...

Has anyone heard about this ???.. Is there a way to override the fail safe mode ??

 

So what sensors have you changed? Also what are using to log to see?

 

I've almost every sensor related to PO0643 to include throttle and acceleration pedal.. I have Osiris and can see the codes, but right now I'm having my brother in law check it with his Snapon diagnostic tool which is more accurate. He believes the problem seems to be electrical and is checking the wire harnesses for proper grounding.
Once I get this going, I will go back and resume with installing the built engine in. I didn't mention it, but last Jan I got the new engine in and had problems with it which caused me to put the original motor back.
I'll keep you posted with the progress.

 

We replaced the engine harness (1 of 3 and it costs an arm and a leg), the one that connects to the ECU and goes into the engine bay. There are no problems now (cross my fingers). The mechanic (my brother in law) was very assertive in diagnosing the problem.