E36 BMW Oxygen (O2) Sensor Replacement - Part I Diagnosing and Symptoms

This article pertains to all E36 BMW models, both 4 cylindf (M42 and M44) and 6 cylinder (M50, M50TU, M52, S50, S52) engine powered cars. As these cars are up to 15 years old now, chances are their oxygen sensor (O2 sensor) has been replaced at least once or currently needs replacing. The oxygen sensor is one of the most important elements of your BMW's fuel injection system. A finely tuned fuel injection system with an oxygen sensor can maintain an air/fuel ratio within a close tolerance of .02 percent. Keeping the engine at the stoichiometric level (14.6:1 air/fuel ratio) helps the engine generate the most power with the least amount of emissions. Why is this important, you might ask, if you are not a racer or automotive performance enthusiast? Well, a junk or failing oxygen sensor can affect driveability of your BMW in many ways.

There are a few signs that your oxygen sensor may be failing. In general, it is difficult to diagnose problems with the sensor, unless all of the other components in the fuel injection system have been checked and determined to be operating correctly. Some of the symptoms of a failed oxygen sensor system are:

Irregular idle during warm-up

Irregular idle with warm engine

Engine will not accelerate and backfires

Poor engine performance

Fuel consumption is high

Driving performance is weak

CO concentration at idle is too high or too low

Check Engine light is illuminated

In general, if the oxygen sensor is not working, the car can run poorly, and will also be generating harmful emissions. As your bosch fuel injection system has several components, it is best to eliminate unknowns before blindly replacing your o2 sensor. However, if the check engine light comes on, you can run a diagnostic test to verify if indeed it is time to replace.

Turn the key to the run position (as opposed to the start position), and press the gas pedal to the floor and release 5 times. Then wait. The check engine light should go off, then flash in a pattern of dashes with specific durations. The E36 factory Bentley Service Manual shows the correct number of flashes. If it matches up, then go to your local parts supplier and order a new sensor. I highly recommend getting the bosch or equivalent oem replacement sensor and not a universal one. You don't save much money by getting the universal one, anyways. Next article will detail oxygen sensor troubleshooting, testing, and replacement instructions for E36 BMW models, including 1992 325i, 1992 325is, 1992 318i, 1992 318is, 1993 325i, 1993 325is, 1993 318i, 1993 318is, 1994 325i, 1994 325is, 1994 318i, 1994 318is, 1995 325i, 1995 325is, 1995 318i, 1995 318is, 1995 318ti, 1995 M3, 1996 328i, 1996 328is, 1996 318i, 1996 318is, 1996 318ti, 1996 M3, 1997 328i, 1997 328is, 1997 318i, 1997 318is, 1997 318ti, 1997 M3, 1998 328i, 1998 328is, 1998 323i, 1998 323is, 1996 318ti, 1998 M3 models.