Code 43 - ESC Error (Without ESC Module): Notes

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 1993 Pontiac Sunbird, 1993 Pontiac Grand Prix, 1993 Oldsmobile Cutlass Supreme, 1993 Chevrolet Lumina, and 1993 Chevrolet Corsica. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Test numbers refer to numbers on diagnostic chart. If an audible knock is heard from engine at idle, repair internal engine problems before proceeding.

If tapping on engine does not produce a knock signal on scan tester, try tapping engine closer to sensor before proceeding.
ECM supplies a 5-volt reference signal on knock sensor line. With knock sensor connected, this signal is pulled low to about 2.5 volts. Knock signal, which is an AC signal, rides on this 2.5-volt DC signal.
This test determines if knock sensor is faulty or if ESC portion of MEM-CAL is faulty.