System Diagnosis - Knock Sensor (KS)

Diagnostic Chart:

Wiring Diagram:

Circuit Description
The Knock Sensor (KS) detects abnormal vibration (spark knocking) in the engine. The sensor is mounted in the engine block near the cylinders. The sensor produces an AC output voltage which increases with the severity of the knock. The amplitude and the frequency are dependent upon the knock level. The knock sensor sends this signal voltage to the Powertrain Control Module (PCM). The PCM will retard the electronic spark timing based on the signal the PCM receives in order to reduce the spark knock.

Diagnostic Aids

^ This table does not check for an open knock sensor signal circuit. If the knock sensor signal circuit is open, a DTC PO325 will be set.
^ While observing the knock signal on the scan tool, there should be an indication that knock is present whenever detonation can be heard. Detonation is most likely to occur under high engine load conditions.

Diagnosis
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.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. This information on the scan tool 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.
4. This checks that the internal resistance of the Knock Sensor is within an acceptable range.
6. Check the Knock Sensor connections for loose terminals or corrosion.