For a complete wiring diagram Refer to Section 8W.Knock is the spontaneous auto-ignition of the remaining fuel/air mixture in the engine combustion chamber that occurs after normal combustion has started. It can occur under extreme vehicle operating conditions such as high engine temperature, high MAP, low humidity, and heavy loads to the engine. Knock is caused by excessive spark advance for the given engine operating conditions. Severe, continuous knock may be caused by carbon deposits, bad gasoline, and/or low octane fuel. Avoiding light audible knock is important for customer satisfaction while preventing excessive knock is important to protect engine components. The output voltage from the knock circuit represents the strength of the engine knock and is read by the engine controller. The knock system output voltage is not zero due to engine background noise, even when knock is not present. When the engine is operated under high load conditions where knock is possible, the knock voltage is tested to decide if it exceeds the knock voltage threshold. Knock has occurred when the knock voltage is at or above this knock threshold. When knock is detected a calibrated short term knock spark retard to be subtracted from the spark advance is calculated. The amount of retarded spark advance is based off a calibrated severity of the knock event. This retarded spark advance is used in the next ignition event to prevent further knock events. If knock continues, an additional amount of short term spark advance retard is added. When knock stops, short term knock spark retard is eliminated, the long term knock spark retard is reduced by a calibrated amount to recover some previously retarded spark advance. This decreases spark retard to improve engine performance. When Monitored:This monitor runs above 2000 rpm, under open throttle conditions. The Knock diagnostic does not run at idle or during decelerations. The high voltage test runs all the times the engine is running.Set Condition:The High voltage fault will set at 4.8 volts. Two Trip Fault. Three good trips to turn off the MIL.Possible Causes(K42) KS SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE(K42) KS SIGNAL CIRCUIT OPEN(K942) KS RETURN CIRCUIT OPEN(K42) KS SIGNAL CIRCUIT SHORTED TO THE (K942) KS RETURN CIRCUIT(K42) KS SIGNAL CIRCUIT SHORTED TO GROUNDKNOCK SENSORPCMAlways perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).1. ACTIVE DTCStart the engine.Allow the engine to reach normal operating temperature.With a scan tool, select View DTCs.It may be necessary to drive the vehicle to meet the conditions to set this DTC, try to repeat the conditions in which the fault originally set by reviewing the Freeze Frame data.Is the DTC Active or Pending at this time?YesGo To 2NoRefer to the INTERMITTENT CONDITION Diagnostic Procedure.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 2. (K42) KS SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE

Turn the ignition off.Disconnect the Knock Sensor harness connector.Disconnect the C2 PCM harness connector.Allow the engine to idle.Measure the voltage on the (K42) KS Signal circuit in the Knock Sensor harness connector.Is the voltage above 1.5 volts at idle and above 0.3 of a volt above 2000 RPM?YesRepair the short to battery voltage in the (K42) KS Signal circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 33. (K42) KS SIGNAL CIRCUIT OPEN

Turn the ignition off.Do 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 #8815 to perform diagnosis.Measure the resistance of the (K42) KS Signal circuit from the Knock Sensor harness connector to the appropriate terminal of special tool #8815.Is the resistance below 5.0 ohms?YesGo To 4NoRepair the open in the (K42) KS Signal circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 4. (K942) KS RETURN CIRCUIT OPEN

Measure the resistance of the (K942) KS Return circuit from the Knock Sensor harness connector to the appropriate terminal of special tool #8815.Is the resistance below 5.0 ohms?YesGo To 5NoRepair the open in the (K942) KS Return circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 5. (K42) KS SIGNAL CIRCUIT SHORTED TO THE (K942) KS RETURN CIRCUIT

Measure the resistance between the (K42) KS Signal circuit and the (K942) KS Return circuit in the Knock Sensor harness connector.Is the resistance below 100 ohms?YesRepair the short between the (K42) KS Signal circuit and the (K942) KS Return circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 66. (K42) KS SIGNAL CIRCUIT SHORTED TO GROUND

Measure the resistance between ground and the (K42) KS Signal circuit in the Knock Sensor harness connector.Is the resistance below 100 ohms?YesRepair the short to ground in the (K42) KS Signal circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 77. KNOCK SENSORReplace the Knock Sensor.Ignition on, engine not running.With the scan tool, erase DTC.Attempt to operate the vehicle using the information noted in the Freeze Frame.With the scan tool, view DTCs.Does the scan tool display the DTC that was previously erased?YesBefore continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary. Replace and program the Powertrain Control Module per Service Information.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoTest Complete.