Oxygen Sensor: Service Precautions

HO2S CONTAMINATION
Contamination of the heated oxygen sensor can result from the use of an inappropriate RTV sealant (not oxygen sensor safe), coolant consumption, or oil consumption. To check for contamination, remove the HO2S and visually inspect the portion of the sensor exposed to the exhaust stream. A contaminated HO2S is indicated by abnormal discoloration of the portion of the sensor exposed to the exhaust stream. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). This condition causes the PCM to reduce the amount of fuel delivered to the engine, causing a severe driveability problem.