Diagnostic Aids

After confirming DTC P0125, use scan tool to access CURRENT DATA to confirm voltage output of A/F sensor. ECM controls voltage of AF+ and AF- circuits at ECM to a fixed voltage of 3.3 volts (at AF+ terminal) or 3.0 volts (at AF- terminal). It is impossible to confirm A/F sensor output voltage without using a scan tool. OBD II scan tools will display A/F sensor voltage as one fifth of that shown on Toyota hand-held tester. Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.

During fuel enrichment, output voltage of A/F sensor may be less than 0.56 volt (2.8 volts on Toyota hand-held tester). During fuel cut, output voltage of A/F sensor may be greater than 0.76 volt (3.8 volts on Toyota hand-held tester). If output voltage of A/F sensor remains at 0.66 volt (3.3 volts on Toyota hand-held tester) during all conditions, A/F sensor circuit may be open. If output voltage of A/F sensor remains at 0.76 volt (3.8 volts on Toyota hand-held tester) or more during all conditions, A/F sensor circuit may be shorted. If output voltage of A/F sensor remains at 0.56 volt (2.8 volts on Toyota hand-held tester) or less during all conditions, A/F sensor circuit may be shorted.