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 Air/Fuel (A/F) sensor monitors exhaust gas oxygen content and delivers input signals to ECM. Heated A/F sensor is located on exhaust pipe in front of catalytic converter. A/F sensor may also be referred to as A/F sensor (bank No. 1 sensor No. 1) or A/F ratio sensor. ECM uses input signals to determine fuel injection system operation. DTC is set when A/F sensor output voltage does not change after engine is started with engine at normal operating temperature, engine speed of 1500 RPM or more and with vehicle speed of 25-62 MPH for at least 1.5 minutes. Possible causes are
- A/F sensor circuit is open or shorted.
- Defective A/F 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 A/F sensor. ECM maintains a fixed voltage of 3.3 volts at AF1+ terminal on ECM and 3.0 volts at AF1- terminal on ECM. It is impossible to confirm A/F sensor output voltage without using Toyota hand-held tester or scan tool. A/F sensor output voltage on scan tool is displayed at one fifth the voltage of that displayed on a Toyota hand-held tester. Using hand-held tester or scan tool, read FREEZE FRAME data. Freeze frame data records engine conditions when malfunction is detected.