Siemens Post-Catalyst Heater

WARNING: This page does not describe the selected car, but rather 14 other vehicles, including the 2003 BMW Z8, 2003 BMW Z4, 2003 BMW X5, 2003 BMW M5, and 2003 BMW M3. However, it is still accessible from the selected car via links, so may be relevant.

Rear oxygen sensor heater is evaluated by monitoring the amount of change that occurs on rear oxygen sensor signal during deceleration/fuel cut-off phase. During deceleration phase, post-cat oxygen sensor is switched to a load resistance value of 100 kW (normal sensor resistance is 30 kW). By switching the resistance of the sensor to 100 kW, sensor voltage is expected to remain within a fixed range (lean). If heater is operating correctly, oxygen sensor signal will remain within a predefined voltage range.

System monitors number of cycles for which sensor voltage remains within fixed range (once per diagnostic cycle). If length of time sensor remains within fixed range is less then predetermined limit, fault will be set. During next drive cycle if heater circuit is monitored and a fault is again present, CHECK ENGINE light will be illuminated. Heater function is monitored once per trip while vehicle is in closed loop operation.