| 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
Heated oxygen sensor No. 1 monitors exhaust gas oxygen content and delivers input signals to ECM. Heated oxygen sensor No. 1 is located on exhaust pipe in front of catalytic converter and may also be referred to as bank No. 1 sensor No. 1, or front oxygen sensor. ECM uses input signals to determine fuel injection system operation. DTC is set when heated oxygen sensor No. 1 voltage remains at .42 volt or more, or .48 volt or less with engine idling and at normal operating temperature. Possible causes are
- Heated oxygen sensor No. 1 circuit is open or shorted.
- Defective heated oxygen sensor No. 1.
- Air induction system malfunction.
- Improper fuel pressure.
- Defective fuel injector.
- 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.