When the Knock Sensor (KS) detects a knock in one of the cylinders, it sends an input signal to the Powertrain Control Module (PCM). In response, the PCM retards ignition timing for all cylinders by a scheduled amount.
Knock sensors contain a piezoelectric material which constantly vibrates and sends an input voltage (signal) to the PCM while the engine operates. As the intensity of the crystal's vibration increases, the knock sensor output voltage also increases.
The voltage signal produced by the knock sensor increases with the amplitude of vibration. The PCM receives as an input the knock sensor voltage signal. If the signal rises above a predetermined level, the PCM will store that value in memory and retard ignition timing to reduce engine knock. If the knock sensor voltage exceeds a preset value, the PCM retards ignition timing for all cylinders. It is not a selective cylinder retard.
The PCM ignores knock sensor input during engine idle conditions. Once the engine speed exceeds a specified value, ignition timing retard is allowed.
Removal & Installation
- Disconnect the negative battery cable.
- Remove the bolt holding the Knock Sensor (KS)
- Remove the KS with the electrical connector attached.
- Disconnect the electrical connector from the KS.
- Attach the electrical connector to the KS.
Install the KS into the engine block. Tighten the bolt to 16 ft. lbs. (22 Nm).
WARNINGOver or under-tightening affects the knock sensor performance.
- Connect the negative battery cable.
- Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Knock Sensor and the Powertrain Control Module (PCM).
- Look for any chafed, pierced, pinched, or partially broken wires.
- Look for broken, bent, pushed out or corroded terminals.
- Monitor the scan tool data relative to this circuit and wiggle test the wiring and connectors.
- Look for the data to change or for the DTC to reset during the wiggle test.
- Refer to any Technical Service Bulletins that may apply.
- Review the scan tool Freeze Frame information. If possible, try to duplicate the conditions under which the DTC set.
- With the engine running at normal operating temperature, monitor the scan tool parameters related to the DTC while wiggling the wire harness. Look for parameter values to change and/or a DTC to set. Turn the ignition off.
Visually inspect the related wire harness. Disconnect all the related harness connectors. Look for any chafed, pierced, pinched, partially broken wires and broken, bent, pushed out, or corroded terminals.
Perform a voltage drop test on the related circuits between the suspected inoperative component and the PCM.
CAUTIONDo not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool no. 8815 to perform diagnosis.
- Inspect and clean all PCM, engine, and chassis grounds that are related to the most current DTC.
- If numerous trouble codes were set, use a wire schematic and look for any common ground or supply circuits.
- For any Relay DTCs, actuate the Relay with the scan tool and wiggle the related wire harness to try to interrupt the actuation.
- For intermittent Evaporative Emission trouble codes perform a visual and physical inspection of the related parts including hoses and the Fuel Filler cap.
- Use the scan tool to perform a System Test if one applies to failing component. A co-pilot, data recorder, and/or lab scope should be used to help diagnose intermittent conditions.