I scanned my car with an OBD II and it displayed trouble code #42. How do you correct the EST signal did not change when the ECM applied bypass voltage to the ignition module. Any suggestions would be greatly appreciated.

A 42 is caused by an inoperative EST system. If the car is older, it might have been set in bypass to set the base ignition timing. If the car is newer, it might be a problem with the ICM, connections, or the ECM.

What year is the car? What engine?