Diagnostic Aids

Short-term and long-term fuel trim value should be within plus or minus 35 percent of each other at 176°F (80°C). 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 A/F sensor output voltage than 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 volts (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 volts (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 volts (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 volts (2.8 volts on Lexus scan tool) or less during all conditions, A/F sensor circuit may be shorted.