Test Group XBMXV02.8M52 & XBMXV02.5M52

WARNING: This page does not describe the selected car, but rather 14 other vehicles, including the 1999 BMW Z3, 1999 BMW M3, 1999 BMW M Roadster, 1999 BMW M Coupe, and 1999 BMW 750iL. However, it is still accessible from the selected car via links, so may be relevant.

General Description - Both oxygen sensors upstream from catalyst are separately monitored for rich and lean voltage, switching time and response time (time is exposed to rich and lean periods).

Switching Time - For monitoring switching time, time from lean to rich and rich to lean mixture is determined and compared with predetermined maximum values which depend on engine RPM and air mass. Relative thresholds (10-90 percent of minimum/maximum amplitude) are used to determine oxygen sensor switching time from lean to rich and rich to lean. Sensor signals are monitored for reversal points while switching time is being measured. If a reversal point is detected, this oxygen sensor signal is not used to determine switching time. Due to switching time fluctuations, results are averaged during monitoring cycle (115 lambda control cycles) before comparing with thresholds. See Figure.

Rich/Lean Periods - To determine switching time, lean and rich period times are added during 115 lambda controller cycles. A malfunction is registered if one or both of the times exceed(s) the thresholds which depend on engine speed and load.

Heater Monitoring - For proper function of oxygen sensor, sensor element must be heated. A non-functioning heater delays sensor readiness for closed loop control and influences emissions. Disconnection, short-to-ground and short-to-battery monitoring and oxygen sensor heater current and voltage monitoring are performed in standard diagnosis function.

Heater Circuit (Upstream Oxygen Sensor) - Due to slow sensor heating in case of low oxygen heating output, rich voltage does not reach its maximum value within a defined time. This reduces oxygen sensor signal amplitude which permits oxygen sensor heating output to be monitored. Malfunction detection is activated every 240 milliseconds independent of engine operation.

Heating Output (Downstream Oxygen Sensor) - Lean sensor voltage is evaluated to diagnose heater circuit. Therefore, this check is performed during deceleration/fuel cut-off phases. Sensor downstream must be switched to a load resistance of 100 ohms (normal operation 30 ohms). During this check, oxygen sensor signal output voltage is controlled to a fixed value (lean limit). If number of cycles during which sensor signal lies within defined limits is smaller than limit, a fault will be stored. Sensor signal is checked every 20 milliseconds during heater circuit diagnosis.