Knock Sensor: Testing and Inspection

Fig. 026 - Wiring Diagram for Electronic Spark Control. VIN 8:

CHART C-5, ELECTRONIC SPARK CONTROL

Electronic spark control is accomplished with a module that sends a voltage signal to the ECM. As the knock sensor detects engine knock, the voltage from the ESC module to the ECM is shut off and this signals the ECM to retard timing.

Fig. 025 Chart C-5 - Electronic Spark Control System Check - No. Code 43:

1. This is the ESC functional check. Simulating an engine knock by tapping the engine block should normally cause an RPM drop (decrease timing). If it doesn't drop, either the timing is not retarding or is retarded all the time.
2. By disconnecting the ESC module, the ECM sees low voltage at terminal "4" and should retard timing. After approximately 4 seconds, "CHECK ENGINE" light will come "ON" and Code 43 will be stored.
3. Checks for proper voltage output (measure on A.C. scale) of knock sensor. Low or no voltage would indicate an open circuit to terminal "E" or faulty sensor.
4. Check engine light should be "on" and a Code 43 set because ESC system would be retarded too long. If no light comes on, the ECM is not retarding the spark because of a voltage on the circuit to terminal "4" or the ECM is faulty.
5. Checks to see if knock sensor is reason for retard signal. If engine knock is not present, and timing increases when knock sensor is disconnected, fault is an over sensitive knock sensor. Timing should not normally increase.
6. Checks to see if retard is due to "noise" on signal wire or faulty controller. If timing increases when wire is disconnected from controller, fault is due to knock sensor signal wire running too close to an ignition or charging system wire. Reroute wire to correct.