Knock Sensor (KS) System Diagnosis

Knock Sensor (KS) System Diagnosis






Circuit Description

The Knock Sensor detects engine detonation. The Powertrain Control Module (PCM) retards the electronic spark timing based on the signal being received. The Knock Sensor produces an AC signal. The amplitude and frequency are dependent upon the knock level. The KS module sends a signal to the PCM. The PCM then retards the spark timing in order to reduce the detonation.

Diagnostic Aids

While observing the knock signal on the scan tool, there should be an indication that a knock is present whenever a knock can be heard. An engine knock is most likely to occur under high engine load conditions.

Test Description

The numbers below refer to the step numbers on the diagnostic table.
1. The OBD System Check prompts the technician to store the Freeze Frame Data in the scan tool. This will create an electronic copy of the Freeze Frame data taken when the fault occurred that can be referred to later.
2. If the engine has an internal problem which is creating a knock, the knock sensor may be responding to the mechanical noise.
3. The scan tool displays knock sensor activity in counts approximately 16-22 at idle. The counts should rise when the engine speed increases and the counts should decrease when the engine speed decreases.
5. This checks that the internal resistance of the knock sensor is within an acceptable range.
7. Inspect the knock sensor connections for loose terminals or corrosion.