Diagnostic Aids

After confirming DTC P0125, use scan tool to access CURRENT DATA to confirm voltage output of A/F sensors (bank No. 1 and 2, sensor No. 1). ECM controls voltage of AFR+, AFL+, AFR- and AFL- terminals at ECM to a fixed voltage of 3.3 volts (at AFR+ and AFL+ terminals) and 3.0 volts (at AFR- and AFL- terminals). It is impossible to confirm A/F sensor output voltage without using a scan tool. A/F sensor output voltage on OBD II scan tools is displayed at one fifth the voltage of that displayed 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 sensors maybe below 0.56 volt (2.8 volts on Toyota hand-held tester). During fuel cut, output voltage of A/F sensors 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.