E36 BMW Oxygen Sensor Replacement Instructions Part II

Continude from the previous article, this will detail the procedure for replacing you E36 BMW's oxygen sensor. The o2 sensor is located in the exhaust system, and senses the oxygen content of the exhaust gases. What does the sensor do? The amount of oxygen in the exhaust varies according to the air/fuel ratio of the fuel injection system. The oxygen sensor produces a small voltage signal that is interpreted by the electronic control unit (ECU) of the fuel injection system. The ECU makes constant adjustments in fuel delivery according to the signal generated by the oxygen sensor in order to maintain the optimum air/fuel ratio.

On most BMWs, the engine's computer will throw the Check Engine Light if the signal received by the computer is out of it's normal range, meaning in all likelihood that you need a new sensor. Chipped cars (those with aftermarket ECU software or for OBDII cars the popular Shark Injector) tend to have shorter replacement intervals. Just a word to the wise.

Some shops recommend a replacement interval as short as 30,000 miles for optimal performance, emissions output, and catalytic converter lifespan. The oxygen sensor is located on exhaust manifold and/or exhaust pipes that lead to the muffler. The exact location changed over model years and E36 model. For example, the M42 and M44 318 models have their sensor located in a difficult place. On my 95 325is, the sensor is located just upstream from the catalytic converter, sitting at an angle on top of the pipe. A large adjustable wrench in thoery fits on there, but you are better off spending $20 to get the right tool for the job, which is an oxygen sensor socket which is a special deep sockety with a slit cut in the side. Unless you have a lift (I know a guy who does, that b@stard!), you will need to jack the car up and put it on jackstands or ramps to get under there.

Using a socket or wrench, simply remove the sensor from the exhaust pipe. The electrical plug for the O2 sensor is removed by simply rotating the plastic retainer counter-clockwise, and the plug should come right off. New O2 sensors should have the same exact plug - ready to attach to your car. On the E36 3-Series, the plug is located towards the right side of the rear of the transmission.

An old worn out 02 sensor will likely be covered with blakc soot. Clean off the mounting bung and use never-seize or some other thread lubricating antiseize compound
on the new oxygen sensor. My new one (for OBD-1 E36 M50 cars ie 325i and 325is is Bosch 134321) came with this good already on it!

You will probably find the supplied cable length is way too long. Use zip to fold the cable over to take up the slack. Keep the cable away the exhaust so you don't melt anything.

If you did everything right, the check engine light should shut off upon restarting when you are done and in most cases the car will run perceptibly better.