A Heated Oxygen Sensor (HO2S) monitors the oxygen content in the three-way catalytic converter and transmits this information to the Powertrain Control Module (PCM). The PCM then adjusts the air/fuel ratio to provide a rich (more fuel) or lean (less fuel) condition.
Perform a visual inspection on the sensor as follows:
- Remove the sensor from the exhaust.
- If the sensor tip has a black/sooty deposit, this may indicate a rich fuel mixture.
- If the sensor tip has a white gritty deposit, this may indicate an internal anti-freeze leak.
- If the sensor tip has a brown deposit, this could indicate oil consumption.
- All these contaminates can destroy the sensor, if the problem is not repaired the new sensor will also be damaged.
- Reinstall the sensor.
- Disconnect the Heated Oxygen Sensor (HO2S). Measure resistance between PWR and GND (heater) terminals of the sensor.
- With the engine hot-to-warm, the resistance should be 5-30 ohms.
- At room temperature, the resistance should be 2-5 ohms. If the readings are within specification, the sensor's heater element is okay.
With the O2S connected and engine running, measure voltage with a DVOM by backprobing the SIG RTN wire of the oxygen sensor connector. The voltage readings at idle should stay below 1 volt. When the speed is increased or decreased, the voltage should fluctuate between 0 and 1 volt; if so, the sensor is okay.