Chart C5 - Electronic Spark Control: Notes

The Electronic Spark Control (ESC) system on these vehicles consists of a knock sensor and an ESC controller which sends a voltage signal to the ECM. As engine knock is detected by the knock sensor, a signal is sent to the ESC controller. The controller responds to this knock signal by cutting off current to ECM on circuit No. 485. The ECM will then retard timing if engine speed is greater than 850 RPM.

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. 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 the knock sensor is faulty, or if the ESC module can't recognize a knock signal.