Electronic Spark Control Module: Testing and Inspection

Chart C-5:

Wiring Diagram For ESC Circuit:

CIRCUIT DESCRIPTION:

Electronic Spark Control (ESC) is accomplished with a module that sends a voltage signal to the ECM. As the sensor detects engine knock, the voltage from the ESC module to the ECM is reduced. This signals the ECM to retard the timing, if engine speed is over approximately 900 rpm.


TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

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 not be any detonation, and if a knock is noticed, an internal engine problem may exist.

2. Usually a knock signal can be generated by tapping on right exhaust manifold. This test can also be performed at idle. Test number one 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 knock 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 illuminate indicating the ground circuit is OK.

5. Contacting circuit 496, with a test light to 12 volts, should generate a knock signal to determine whether the knock sensor is faulty, or the ESC module can not recognize a knock signal.



DIAGNOSTIC AIDS:

^ "Scan" tools have two positions to diagnose the ESC system. The Knock signal can be monitored to see if the knock sensor is detecting a knock condition, and if the ESC module is functioning. The knock signal should display "YES" whenever an engine detonation is present. The knock retard position on the "Scan" tool displays the amount of spark retard the ECM commands. The ECM can retard the timing up to 20 degrees.

^ If the ESC system checks OK, but detonation is the complaint, refer to Diagnosis By Symptom Testing and Inspection