P0325
P0325-KNOCK SENSOR 1 CIRCUITP0325-Knock Sensor 1 Circuit:
Theory of Operation
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) Knock sensor no.1 signal circuit shorted to battery voltage
- (K42) Knock sensor no.1 signal circuit open
- (K942) Knock sensor no.1 return circuit open
- (K42) Knock sensor no.1 signal circuit shorted to the (K942) knock sensor no.1 return circuit
- (K42) Knock sensor no.1 signal circuit shorted to ground
- Knock sensor
- PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Diagnostic Test
1. ACTIVE DTC
Ignition on, engine not running.
With a scan tool, read DTCs.
Q: Is the DTC active at this time?
YES: Go To 2
NO: Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Component Tests and General Diagnostics
Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
2. (K42) KNOCK SENSOR NO.1 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) Knock Sensor No.1 Signal circuit in the Knock Sensor harness connector.
Q: Is the voltage above 1.5 volts at idle and above 0.3 of a volt above 2000 RPM?
YES: Repair the short to battery voltage in the (K42) Knock Sensor No.1 Signal circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 3
3. (K42) KNOCK SENSOR NO.1 SIGNAL CIRCUIT OPEN
Turn the ignition off.
CAUTION: 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) Knock Sensor No.1 Signal circuit from the Knock Sensor harness connector to the appropriate terminal of special tool #8815.
Q: Is the resistance below 5.0 ohms?
YES: Go To 4
NO: Repair the open in the (K42) Knock Sensor No.1 Signal circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
4. (K942) KNOCK SENSOR NO.1 RETURN CIRCUIT OPEN
Measure the resistance of the (K942) Knock Sensor No.1 Return circuit from the Knock Sensor harness connector to the appropriate terminal of special tool #8815.
Q: Is the resistance below 5.0 ohms?
YES: Go To 5
NO: Repair the open in the (K942) Knock Sensor No.1 Return circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
5. (K42) KNOCK SENSOR NO.1 SIGNAL CIRCUIT SHORTED TO THE (K942) KNOCK SENSOR NO.1 RETURN CIRCUIT
Measure the resistance between the (K42) Knock Sensor No.1 Signal circuit and the (K942) Knock Sensor No.1 Return circuit in the Knock Sensor harness connector.
Q: Is the resistance below 100 ohms?
YES: Repair the short between the (K42) Knock Sensor No.1 Signal circuit and the (K942) Knock Sensor No.1 Return circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 6
6. (K42) KNOCK SENSOR NO.1 SIGNAL CIRCUIT SHORTED TO GROUND
Measure the resistance between ground and the (K42) Knock Sensor No.1 Signal circuit in the Knock Sensor harness connector.
Q: Is the resistance below 100 ohms?
YES: Repair the short to ground in the (K42) Knock Sensor No.1 Signal circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 7
7. KNOCK SENSOR
Replace 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, read DTCs.
Q: Does the scan tool display the DTC that was previously erased?
YES:
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary. Replace and program the Powertrain Control Module. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Test Complete.