Diagnostic Aids

WARNING: This page is about a different car, the 2002 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.

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 (3.3 volts at AFR+ and AFL+ terminals; 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 data records engine conditions when malfunction is detected.

During fuel enrichment, output voltage of A/F sensors may be less than 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.