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 AFL+ and AFL- terminals at ECM to a fixed voltage (3.3 volts at AFL+ terminal; 3.0 volts at AFL- terminal). 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 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.