Diagnostic Aids

WARNING: This page is about a different car, the 2002 Lexus RX 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 heated 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+ or AFL+ terminal; 3.0 volts at AFR- or AFL- terminal). It is impossible to confirm A/F sensor output voltage without using a scan tool. OBD-II scan tools will display one fifth of A/F sensor output voltage that Lexus scan tool will. 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 may be less than 0.56 volt (2.8 volts on Lexus scan tool). During fuel cut, output voltage of A/F sensors may be more than 0.76 volt (3.8 volts on Lexus scan tool). If output voltage of A/F sensor remains at 0.66 volt (3.3 volts on Lexus scan tool) 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 Lexus scan tool) 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 Lexus scan tool) or less during all conditions, A/F sensor circuit may be shorted.