Diagnostic Aids
WARNING: This page does not describe the selected car, but rather 26 other vehicles, including the 1999 Mercury Tracer, 1999 Mercury Sable, 1999 Mercury Mystique, 1999 Mercury Mountaineer, and 1999 Mercury Grand Marquis. However, it is still accessible from the selected car via links, so may be relevant.
Perform this test only when directed by QUICK TEST. This test is intended to diagnose the following:
- Knock Sensor (KS).
- Wiring harness circuits (KS and SIG RTN).
- Powertrain Control Module (PCM).
To prevent replacement of good components, be aware the following non-EEC related areas may be at fault:
- Poor fuel quality.
- Ignition system.
- Ignition or valve timing.
- Engine mechanical condition.
- 1) Check Knock Sensor Voltage
DTCs P0325, P0326, P0330 and P0331 indicate spark knock system failed. DTC P0325 and P0326 are for knock sensor No. 1 (cylinder bank that includes cylinder No. 1). DTCs P0326 and P0331 are for knock sensor No. 2. Possible causes for these faults are:- Open or short in harness.
- Faulty knock sensor.
- Faulty Powertrain Control Module (PCM).
Turn ignition off. Ensure knock sensor is connected. Perform COMPREHENSIVE COMPONENT MONITOR REPAIR VERIFICATION DRIVE CYCLE. See DRIVE CYCLES under ADDITIONAL SYSTEM FUNCTIONS. Turn ignition on. Using scan tool, select KS PID from PID/DATA monitor menu. If PID voltage is less than .5 volt, go to next step. If PID voltage is .5 volt or more, go to step 5).
- 2) Check Knock Sensor Resistance
Turn ignition off. Disconnect knock sensor connector. Measure resistance between knock sensor terminals. See Fig 1, Fig 2, Fig 4 or Fig 5 . If resistance is 4.39-5.35 megohms, go to step 7) (models without shielded knock sensor) or step 6) (models with shielded knock sensor). See Fig 4. If resistance is more than 5.35 megohms, go to next step. If resistance is less than 4.39 megohms, go to step 5). - 3) Check For Open Circuit
Disconnect PCM connector. Measure resistance of KS sensor circuits between PCM and knock sensor wiring harness connector. See Fig 1-Fig 7 . If all resistance readings are less than 5 ohms, replace knock sensor. If any resistance reading is 5 ohms or more, repair open circuit. - 4) Check Circuit For Short To Ground
Disconnect PCM connector. Measure resistance of each knock sensor circuit between ground and appropriate PCM connector pin. If all resistance readings are more than 10,000 ohms, replace knock sensor. If any resistance reading is 10,000 ohms or less, repair short to ground. - 5) Check Circuit For Short To Power
Turn ignition on. Measure voltage between PCM connector pin No. 57 and ground. If voltage is less than .5 volt, replace PCM. If voltage is .5 volt or more, repair short to power. - 6) Check Shield Circuit Resistance
Measure resistance between PCM connector pin No. 24 and shield terminal at knock sensor wiring harness connector. See Fig 4. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in knock sensor shield circuit. - 7) Check PCM For Short To Ground
Ensure ignition is off. Connect PCM connector. Measure resistance between knock sensor wiring harness connector terminals. If resistance is more than 10,000 ohms, replace knock sensor. Reconnect all components and repeat QUICK TEST . If fault is still present, replace PCM. If resistance is 10,000 ohms or less, replace PCM.NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 7) to step 15). No test procedures have been omitted. - 15) Check Knock Sensor Voltage
DTCs P0326 (KS1) and P0331 (KS2) indicate spark knock has not been sensed. DTCs P0325 (KS1) and P0330 (KS2) indicate spark knock system failed. Possible causes for these faults are:- Open or short in harness.
- Faulty knock sensor.
- Faulty Powertrain Control Module (PCM).
Turn ignition on. Using scan tool, select KS PID from PID/DATA monitor menu. If PID voltage is 2.2-2.6 volts, turn ignition off and go to next step. If PID voltage is not 2.2-2.6 volts, go to step 18).
- 16) Check For Intermittent Circuit Fault
While observing KS PID voltage, wiggle small sections of wiring harness starting at the knock sensor working toward PCM. If fault is indicated (voltage changes), isolate fault and repair as necessary. If no fault is indicated, go to next step. - 17) Check For Voltage Increase
Turn ignition off. Disconnect scan tool Data Link Connector (DLC). Set voltmeter on AC scale. Start engine and allow to idle. Measure voltage between suspect sensor terminals. See Fig 3, Fig 6 or Fig 7 . Note voltage reading. Raise engine speed to 3000 RPM. If AC voltage increases, proceed as follows:- If no DTCs are present, no problem is indicated at this time. Diagnose by symptom. See TROUBLE SHOOTING - NO CODES - EEC-V article.
- If any DTCs are present, replace PCM.
- 18) Check Circuit Resistance
Turn ignition off. Disconnect PCM connector. Disconnect suspect knock sensor. Measure resistance of KS circuit (KS, KS1 or KS2) between suspect sensor wiring harness connector and PCM connector pin No. 32 (KS2) or 57 (KS or KS1). Also measure resistance of SIG RTN circuit between suspect sensor wiring harness connector and PCM connector pin No. 91. If both resistance readings are less than 5 ohms, go to next step. If any resistance reading is 5 ohms or more, repair open circuit. - 19) Check Circuit For Short To Ground
Measure resistance between PCM connector pin No. 32 (KS2) or 57 (KS or KS1) and ground. If resistance is more than 10,000 ohms, replace knock sensor. If resistance is 10,000 ohms or less, repair short circuit.
Fig 1: Identifying Knock Sensor Circuits (Contour, Econoline 4.2L, Escort ZX2, Expedition, Explorer - 4.0L OHV, Mountaineer - 4.0L OHV, Mystique, Navigator, F150 & F250 - 2.4L, 4.6L & 5.4L Light-Duty)
Fig 2: Identifying Dual Knock Sensor Circuits & Connector Terminals (Continental & Mustang 4.6L 4-Valve)
Fig 4: Identifying Knock Sensor Circuits & Connector Terminals (Econoline - 5.4L Super-Duty & 6.8L, F Super-Duty Pickups - 5.4L & 6.8L & Town Car)