Bosch Oxygen Sensor - E28 M5 & E24 M6

Bosch Oxygen Sensor for E28 M5 (1987, 1988) and E24 M6 (1987, 1988, 1989) with the S38 Engine

Signs of an O2 sensor failure include worse fuel economy, lack of torque, hard starting, and fault codes for the sensor. It is a good idea to replace the O2 sensor at regular intervals rather than waiting for a failure. Since the performance degrades over time you may not even notice the loss in performance or economy.