| WARNING | Read service precautions before proceeding with service procedure. See SERVICE PRECAUTIONS . |
| CAUTION | If Engine Control Module (ECM) replacement is instructed in following test, always ensure ECM electrical connectors and ground circuits are okay. If either are defective, repair and repeat testing to confirm ECM malfunction. |
Circuit Description
Knock sensor generates voltage when engine block vibrates due to knocking. DTC is set when there is no knock sensor signal to ECM with engine speed is 2000 RPM or more. If DTC P0325 exists, ECM will operate in fail-safe mode which retards the ignition timing to a maximum setting. Possible causes are
- Knock sensor circuit is open or shorted.
- Defective or loose knock sensor.
- Defective ECM.
Diagnostic Aids
Using Toyota hand-held tester or scan tool, read FREEZE FRAME data. Freeze frame data records engine conditions when malfunction is detected.
Normal mode vibration frequency of knock sensor is 8.1 kHz. If oscilloscope is available, knock sensor operation may be checked by reading knock sensor signal waveform patterns with engine at 4000 RPM by connecting oscilloscope between body ground and terminal No. 28 (Black wire) at ECM electrical connector E7. This is the KNK1 terminal on ECM. ECM is located behind the glove box. see scheme 3 For ECM electrical connector terminal identification see scheme 7 Knock sensor waveform patterns should be properly displayed. (Scheme 314)
Scheme 314
- Ensure ignition is off. Remove glove box for access to ECM with electrical connectors still installed on ECM. see scheme 3 Disconnect ECM electrical connector E7. see scheme 7
- Using ohmmeter, check resistance between body ground and terminal No. 28 (Black wire) at ECM electrical connector E7. This is the KNK1 terminal on ECM. Resistance should be one megohm or more. If resistance is not within specification, go to next step. If resistance is within specification, go to step 4.
- Check knock sensor. See KNOCK SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - 4-CYLINDER article. If knock sensor is okay, go to next step. If knock sensor is defective, replace knock sensor.
- Check for open and short in Black wire and electrical connectors between knock sensor and ECM. See WIRING DIAGRAMS article. If wiring and electrical connectors are okay, go to next step. If wiring or electrical connector is defective, repair as necessary.
- Replace knock sensor with a known-good knock sensor. For servicing of knock sensor, see KNOCK SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - 4-CYLINDER article. Using Toyota hand-held tester or scan tool, clear DTCs from ECM. Recheck for DTCs. If DTC P0325 still exists, replace ECM. If DTC P0325 does not exist, the original knock sensor was defective.