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 sensors located on each exhaust manifold monitor exhaust gas oxygen content and deliver input signals to ECM. Heated oxygen sensor on driver's side exhaust manifold may be referred to as bank No. 1 sensor No. 1 and heated oxygen sensor on passenger's side exhaust manifold may be referred to as bank No. 2 sensor No. 1. ECM uses input signal to determine fuel injection system operation. DTC is set when heated oxygen sensor output voltage does not change after engine is started with engine at normal operating temperature, engine speed of 1400 RPM or more and with vehicle speed of 25-62 MPH for at least 3 minutes. Possible causes are
- Heated oxygen sensor circuit is open or shorted.
- Defective heated oxygen sensor.
- Air induction system malfunction.
- Improper fuel pressure.
- Defective fuel injector.
- Exhaust system leak.
- 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 output voltage for heated oxygen sensor on each exhaust manifold (bank No. 1 sensor No. 1 and bank No. 2 sensor No. 1). If output voltage is always less than .1 volt, heated oxygen sensor 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.