I thought this was interesting. Might help someone else too

Quote Originally Posted by rock auto
The Other End of the Oxygen Sensor





Oxygen sensors thread into the exhaust system where they obviously face extreme heat and harsh exhaust gases. Oxygen sensors fail when the bulb inside the exhaust pipe is exposed to lead, silicone, antifreeze, engine oil and other contaminants. Many people are not aware of the role that the other end of the oxygen sensor plays. Surprisingly, the visible end of the sensor with the wire pigtail is just as important and sensitive to contamination as the end slugging it out in the exhaust pipe.

Nearly all oxygen sensors are designed to measure the difference between the oxygen level in the exhaust with the oxygen level in the outside air. The sensor generates a voltage based on the difference in oxygen levels that the engine computer uses to continuously adjust the fuel mixture, etc. The outside air the oxygen sensor needs for its comparison enters the sensor at the end with the wire pigtail. Depending on the sensor design, the air might enter through a dedicated hole or through the wires.



The oxygen sensor ambient air inlet is likely to be protected by silicone boots, porous PTFE (Teflon) or some other means. A routine splash of water is not likely to hurt an oxygen sensor, but leaking chemicals (engine oil, power steering fluid, etc.) can clog or enter the oxygen sensor air inlet and damage the sensor. Efforts to “protect” oxygen sensors by spraying them with lubricant, covering them with insulation, etc. can backfire if the sensor’s air inlet is blocked or contaminated.

Oxygen sensor installation instructions emphasize that the entire sensor, including the wiring harness, is part of an integrated system. Routing and connecting the wires is as important as carefully threading the sensor into the warm exhaust pipe. I just read installation instructions for a Bosch oxygen sensor that had just two steps covering removing the old sensor and screwing the new sensor into the exhaust port. The instructions had ten steps covering the connection and routing of the oxygen sensor’s four wires.

The oxygen sensor bulb buried in the exhaust pipe is on its own, but you can maintain the other end by making sure the wiring harness is never torn, rerouted or covered with goop.

Tom Taylor,
RockAuto.com
http://www.rockauto.com/Newsletter/index.html#trivia