Knock Sensor (KS) System Description
Purpose
Varying octane levels in today's gasoline may cause detonation in some engines. Detonation is caused by an uncontrolled explosion (burn) in the combustion chamber. This uncontrolled explosion could produce a flame front opposite that of the normal flame front produced by the spark plug. The rattling sound normally associated with detonation is the result of two or more opposing pressures (flame fronts) colliding within the combustion chamber. Though light detonation is sometimes considered normal, heavy detonation could result in engine damage. To control spark knock, a knock sensor (KS) system is used. This system is designed to retard spark timing when spark knock is detected in the engine. The KS system allows the engine to use maximum spark advance for optimal driveability and fuel economy.
Operation
The PCM contains integrated knock sensor (KS) diagnostic circuitry. Input signals from the knock sensors are used to detect engine detonation, allowing the PCM to retard ignition control (IC) spark timing based on the amplitude and frequency of the KS signal being received.
The knock sensors detect abnormal vibration (spark knocking) in the engine. The knock sensors are mounted in the engine block near the cylinders. The knock sensors produce an AC signal voltage under all engine operating conditions. During engine operation, the PCM calculates the average voltage of each knock sensor's signal. If the knock sensor system is operating normally, the PCM should monitor KS signal voltage varying over 0.5 volt above and below the calculated average voltage.
Diagnosis
If the PCM malfunctions in a manner which will not allow proper diagnosis of the KS circuits, DTC P0325 will set.
DTCs P0327 and P0332 are designed to diagnose the knock sensors, and related wiring, so problems encountered with the KS system should set a DTC. However, if no DTC was set but the KS system is suspect because detonation was the customer's complaint, refer to Detonation/Spark Knock .
Detonation/Spark Knock
Fuel System
• Check for low fuel pressure. Refer to Fuel System Pressure Test (VIN K) or Fuel System Pressure Test (VIN 1) .
• Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
• Check items that can cause an engine to run lean (Long Term FT significantly in the positive range). Refer to Diagnostic Aids for DTC P0171 Fuel Trim System Lean .
Ignition System
- Check the spark plugs for proper heat range and reach.
Engine Cooling System
Check for obvious overheating problems:
• Low engine coolant.
• Restricted air flow to radiator, or restricted water flow through radiator.
• Inoperative electric cooling fan circuits. Refer to Electric Cooling Fan Diagnosis .
• Correct coolant solution should be a 50/50 mix of GM 1052753 or equivalent antifreeze coolant and water. Refer to Cooling System Draining and Filling in Engine Cooling.
Engine Mechanical
• Excessive oil in combustion chamber-Leaking valve seals. Refer to Valve Stem Oil Seal and Valve Spring Replacement in Engine Mechanical.
• Low cylinder compression. Refer to Engine Compression Test in Engine Mechanical.
• Combustion chambers for excessive carbon buildup. Clean using top engine cleaner. Follow instructions on can.
• For incorrect basic engine parts. Inspect the following:
- Camshaft
- Cylinder heads
- Pistons, etc.
• Refer to Engine Compression Test in Engine Mechanical.
Additional Checks
• Check for proper EGR system operation. Refer to DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient .
• Check the transaxle range switch input with the vehicle in drive and the gear selector in drive or overdrive.
• Check TCC operation. TCC applying too soon can cause the engine to spark knock. Refer to Diagnostic Starting Point - Automatic Transmission in Automatic Transaxle.
• If scan tool readings are normal and there are no engine mechanical faults, fill the fuel tank with a known quality gasoline that has a minimum octane reading of 87 (for VIN K, 91 for VIN 1) and re-evaluate vehicle performance.
DTC P0325 Knock Sensor (KS) Circuit
Circuit Description
The PCM contains integrated knock sensor (KS) diagnostic circuitry. Input signals from the knock sensors are used to detect engine detonation, allowing the PCM to retard ignition control (IC) spark timing based on the amplitude and frequency of the KS signal being received. The knock sensors produce an AC signal under all engine operating conditions. During engine operation, the PCM calculates the average voltage of each knock sensors signal. If the knock sensor system is operating normally, the PCM should monitor KS signal voltages varying over 0.5 volt above and below the calculated average voltage. If the PCM malfunctions in a manner which will not allow proper diagnosis of the KS circuits, DTC P0325 will set.
Conditions for Running the DTC
• No TP sensor, VSS, CKP, MAF, or ECT DTCs are set
• VIN K - Engine speed is between 1000-4000 rpm.
• VIN 1 - Engine speed is between 1000-3000 rpm.
• VIN K - Throttle angle is more than 3 percent.
• VIN 1 - Throttle angle is more than 15 percent.
• VIN K - Engine load is more than 20 percent.
• VIN 1 - Engine load is more than 45 percent.
• Engine coolant temperature is more than 75°C (167°F).
• Maximum spark retard is less than 15°.
• System voltage is more than 9 volts.
Conditions for Setting the DTC
• The PCM detects a malfunction in the integrated knock sensor diagnostic circuitry which will not allow proper diagnosis of the knock sensor circuits.
• Above conditions for at least 1 second.
Action Taken When the DTC Sets
The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.
DTC P0327 Knock Sensor (KS) Circuit
Circuit Description
The PCM contains integrated knock sensor (KS) diagnostic circuitry. Input signals from the knock sensors are used to detect engine detonation, allowing the PCM to retard ignition control (IC) spark timing based on the amplitude and frequency of the KS signal being received. The knock sensors produce an AC signal under all engine operating conditions. During engine operation, the PCM calculates the average voltage of each knock sensors signal. If the knock sensor system is operating normally, the PCM should monitor KS signal voltages varying over 0.5 volt above and below the calculated average voltage. If the PCM detects a knock sensor 1 signal voltage within the calculated average voltage range, DTC P0327 will set.
Conditions for Running the DTC
• No TP sensor, VSS, CKP, MAF, or ECT DTCs are set
• VIN K - Engine speed is between 1000-4000 rpm.
• VIN 1 - Engine speed is between 1000-3000 rpm.
• VIN K - Throttle angle is more than 3 percent.
• VIN 1 - Throttle angle is more than 15 percent.
• VIN K - Engine load is more than 20 percent.
• VIN 1 - Engine load is more than 45 percent.
• Engine coolant temperature is more than 75°C (167°F).
• Maximum spark retard is less than 15 degrees.
• System voltage is more than 9 volts.
Conditions for Setting the DTC
The PCM detects a knock sensor 1 signal voltage within the calculated average voltage range.
Action Taken When the DTC Sets
The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.
Diagnostic Aids
Check for the following conditions:
• Poor connection at the PCM or knock sensor 1.
Inspect knock sensor 1 and PCM connectors for backed out terminals, broken locks, and improperly formed or damaged terminals.
• Misrouted harness.
Inspect the knock sensor harness to ensure that it is not routed too close to high voltage wires such as spark plug leads.
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
DTC P0332 Knock Sensor (KS) 2 Circuit
Circuit Description
The PCM contains integrated knock sensor (KS) diagnostic circuitry. Input signals from the knock sensors are used to detect engine detonation, allowing the PCM to retard ignition control (IC) spark timing based on the amplitude and frequency of the KS signal being received. The knock sensors produce an AC signal under all engine operating conditions. During engine operation, the PCM calculates the average voltage of each knock sensor's signal. If the knock sensor system is operating normally, the PCM should monitor KS signal voltages varying over 0.5 volt above and below the calculated average voltage. If the PCM detects a knock sensor 2 signal voltage within the calculated average voltage range, DTC P0332 will set.