Chart C-5 Knock Sensor (KS) System Check

Knock Sensor (KS) System Check:

Knock Sensor Circuit:

CIRCUIT DESCRIPTION
The knock sensor (KS) system is used to detect engine detonation. The Powertrain Control Module (PCM) will retard the spark timing based on signals from the KS module. The knock sensor produces an AC voltage which is sent to the KS module. The amount of AC voltage produced by the sensor is determined by the amount of knock. The circuitry within the knock sensor causes the PCM's 5 volts to be pulled down so that under a no knock condition, CKT 496 would measure about 1.5 volts.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. With engine idling, there should not be a knock signal present at the PCM, because detonation is not likely under a no load condition.
2. Tapping on the engines right side exhaust manifold should simulate a knock signal to determine if the sensor is capable of detecting detonation. If no knock is detected, try tapping on engine block closer to the sensor before replacing the sensor.
3. If the engine has an internal problem which is creating a knock, the knock sensor may be responding to the internal failure.
4. This test determines if a knock sensor is faulty or if the problem is elsewhere in the circuit.
5. Replace KS module with a known good module. If the malfunction is not corrected, install a new PCM with the original KS module.

DIAGNOSTIC AIDS
While observing knock signal on the Tech 1 (or equivalent) Scanner, there should be an indication that knock is present when detonation can be heard. Detonation is most likely to occur under high engine load conditions.