| 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
Heated oxygen sensor monitors exhaust gas oxygen content and delivers input signals to ECM. Heated oxygen sensor is located on exhaust pipe, behind catalytic converter. Heated oxygen sensor may also be referred to as oxygen sensor (bank No. 1 sensor No. 2). ECM uses input signals to determine fuel injection system operation. DTC is set when heated oxygen sensor heater current draw exceeds 2.35 amps or is .2 amp or less when heater operates. If DTC P0141 exists, ECM will operate in fail-safe mode and turn off heater for heated oxygen sensor. Possible causes are
- Heated oxygen sensor circuit is open or shorted.
- Defective heated oxygen 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.
Scheme 252
- Remove glove box and heater duct (if necessary) for access to ECM with electrical connectors still installed on ECM. see scheme 2 Turn ignition on. Using voltmeter, check voltage between body ground and terminal No. 9 (Red/White wire) at ECM electrical connector E4. see scheme 4 This is the HTS terminal on ECM. Voltage should be 9-14 volts. If voltage is not within specification, go to next step. If voltage is within specification, replace ECM.
- Disconnect electrical connector for heated oxygen sensor. Heated oxygen sensor is located on exhaust pipe, behind catalytic converter. Using ohmmeter, check resistance between +B and HT terminals on electrical connector for heater on heated oxygen sensor. (Scheme 252) Resistance should be 11-16 ohms at 68°F (20°C) and 23-32 ohms at 1472°F (800°C). If resistance is within specification, go to next step. If resistance is not within specification, replace heated oxygen sensor.
- Check wiring harness and electrical connectors between ECM and heated oxygen sensor, and between heated oxygen sensor and EFI main relay. See WIRING DIAGRAMS article. EFI main relay may also be referred to as EFI relay. EFI main relay is located in fuse/relay box at driver's side front corner of engine compartment.