Chart C-5, Electronic Spark Control (ESC) System Check: Notes

The knock sensor is used to detect engine detonation and ECM will retard the electronic spark timing based on signal being received. The circuitry, within the knock sensor, causes ECM's supplied 5-volt signal to be pulled down so that under a no knock condition, circuit No. 496 would measure about 2.5 volts. The knock sensor produces an AC signal, which rides on the 2.5 volts (DC voltage). The amplitude and frequency are dependent upon the knock level.

The MEM-CAL used with this engine, contains functions which were part of remotely mounted ESC modules used on other GM vehicles. The ESC portion of the MEM-CAL, sends a signal to other parts of the ECM which adjusts spark timing to retard spark and reduce detonation.

1. With engine idling, there should not be a knock signal present at ECM, because detonation is not likely to occur under no load condition.
2. Tapping engine lift hook should simulate a knock signal to determine if sensor is capable of detecting detonation. If no knock is detected, try tapping on engine block closer to sensor before replacing sensor.
3. If engine has an internal problem which is creating a knock, knock sensor may be responding to internal failure.
4. This test determines if knock sensor is faulty or if ESC portion of MEM-CAL is faulty. If it is determined that MEM-CAL is faulty, ensure that it is properly installed and latched into place. If not properly installed, repair and retest.