Electronic Spark Control (ESC) Check (All Engines)

The knock sensor is used to detect engine detonation and the ECM will retard the electronic spark timing based on the signal being received. The circuitry within the knock sensor causes the ECM's 5 volts 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 the functions which were part of remotely mounted ESC modules used on other General Motors vehicles. The ESC portion of the Mem-Cal sends a signal to other parts of the ECM which retards the spark timing and reduce detonation.

1. If a Code 43 is not set, but a knock signal is indicated while running at 1500 RPM, listen for an internal engine noise. Under a no load condition, there should be no detonation, and if knock is indicated, an internal engine problem may exist.
2. Usually a knock signal can be generated by tapping on the right exhaust manifold. This test can also be performed at idle. Test No. 1 was run at 1500 RPM to determine if a constant knock signal was present, which would affect engine performance.
3. This tests whether the knock signal is due to the sensor, a basic engine problem, or the ESC module.
4. If the module ground circuit is faulty, the ESC module will not function correctly. The test light should light indicating the ground circuits are okay.
5. Contacting circuit No. 496, with a test light to 12 volts, should generate a knock signal to determine if it is faulty, or if the ESC module can't recognize a knock signal.