System Diagnosis - Knock Sensor (KS)

Diagnostic Chart:

Wiring Diagram:

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 (KS). 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.

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 P0325 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.

Test Description

Number(s) below refer to 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 and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference. If a DTC P0325 is set, do not use this table.

2. With the engine idling, there should be not be a knock signal present because detonation is not likely under a no load condition.

3. If the engine has an internal problem which is creating a knock, the knock sensor may be responding to the mechanical noise.

4. Tapping on the engine near the sensor simulates a knock. This step determines if the sensor can respond to an engine noise.

5. The sensor will not produce any voltage unless a knock is present. Voltage present at the sensor indicates that the sensor is malfunctioning.

6. This step will determine if the reason the knock sensor did not respond to the tapping was due to a malfunctioning sensor, KS module or PCM.

7. If the knock sensor signal circuit is routed to close to ignition circuitry, the circuit may be picking up induced electrical noise causing a false knock signal.

10. Reprogram the replacement PCM.