Knock Sensor: Testing and Inspection

Knock Sensor Circuit:

CIRCUIT DESCRIPTION
The Knock Sensor (KS) is used to detect engine detonation. The Powertrain Control Module (PCM) will retard 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 will than retard the spark timing to reduce the detonation.

Knock Sensor (KS) Location:

DIAGNOSTIC AIDS
While observing the knock signal on the scan tool, there should be an indication that knock is present whenever knock can be heard. Engine knock is most likely to occur under high engine load conditions.
Use the following scan tool parameters when diagnosing this circuit.
- KS Noise Channel - This is used to monitor the input signal from the knock sensor. This position should display "YES" when knock is being detected and "NO" when no knock is being detected.
- KS Retard - This indicates how many degrees the PCM is retarding the spark timing.
- KS Active Cntr. - This displays the AC signal from the knock sensor. The scan tool will display KS activity in counts. The higher the counts the more knock that is being detected.

Knock Sensor (KS) System Check:

TEST DESCRIPTION
Test Description Number(s) below refer to the step number(s) 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 knock sensor is within an acceptable range.
7. Check the knock sensor connections for loose terminals or corrosion.