| WARNING | Read service precautions before proceeding with service procedure. See SERVICE PRECAUTIONS . |
Note. This DTC may be caused by the vehicle running out of fuel.
| 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 No. 1 does not output a rich condition (output voltage equal to or more than .45 volt) within 20 seconds after engine is started with engine at normal operating temperature, engine speed of 800 RPM or more and with vehicle speed of 25-62 MPH for at least 50 seconds. Possible causes are
- Fuel system malfunction.
- Air induction system malfunction.
- Defective fuel injector.
- Ignition system malfunction.
- Exhaust system leak.
- Heated oxygen sensor No. 1 circuit is open or shorted.
- Defective heated oxygen sensor No. 1.
- Vehicle has run out of fuel.
- Defective ECM.
Diagnostic Aids
After confirming DTC P0125, use Toyota hand-held tester or scan tool to access CURRENT DATA to read heated oxygen sensor No. 1 output voltage. If output voltage is always less than .1 volt, heated oxygen sensor No. 1 circuit may be open or shorted. Using hand-held tester or scan tool, read FREEZE FRAME data. Freeze frame data records engine conditions when malfunction is detected.