Visually check the connector, making sure it is engaged properly and all of the terminals are straight, tight and free of corrosion.
Detach the sensor electrical connector and check resistance between terminals C and D. Resistance should be 10-15 ohms at 79°F. If resistance is not within specifications, the sensor heater is faulty.
If resistance is within specification, check for battery positive (B+) between connector terminals C and D with the ignition
. If battery positive (B+) is not present, check the circuit continuity back to the PCM. If the circuits are functioning properly, the PCM may be faulty.
Fig. Schematic of a Heated Oxygen Sensor (HO2S) circuit
Check the HO2S sensor voltage between terminals A and B with the engine
. The voltage should be between 350-500 millivolts. If the voltage doesn't fall within that range, the sensor is faulty.
If the voltage is within specifications, recheck the voltage after heating the engine to normal operating temperature. With the engine running at 1200 rpm, then voltage should vary between 100-900 millivolts. If the voltage is not varying or not within the range, the sensor is faulty.
If the voltage is within specifications, check the circuits back to the PCM for continuity.
If the sensor and circuits are functioning properly, the PCM may be faulty.