Circuit Description

NOTE: Some models are equipped with 2 oxygen sensors. On these models, Code 45 will set if the left sensor circuit is rich. Code 65 will set if the right sensor circuit is lean. Use this chart for Code 65 also and perform tests for applicable sensor.

O2 sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600°F (316°C). An open sensor circuit or cold sensor causes "open loop" operation. Code 45 indicates a rich exhaust. Diagnosis should begin with fuel pressure, leaking injector, ignition shielding (ground), vapor canister fuel saturation, coolant sensor, MAP sensor, O2 sensor contamination and TPS intermittent output.

Code is set when fuel system is operating in "closed loop", throttle angle is greater than idle, O2 sensor signal at control module is greater than .7 volt for a precalibrated period, fuel system is attempting to lean mixture and time since engine start is one minute or more. Most likely causes of code are: an actual rich condition, a short to voltage on sensor signal circuit or a faulty PCM.