BOSCH Oxygen Sensor

BOSCH Oxygen Sensors

















The MS42.0 system uses Bosch LSH 25 oxygen sensors that function basically the same as previously used (in Bosch systems). The voltage range is between 0 - 800 mV

The location has changed, the pre-cat sensors are mounted on top of the exhaust manifolds. The catalysts are now integral with the exhaust manifolds (further detailed in the M52 TU engine section).


Oxygen Sensor Signal Influence on Injector "Open" Time

The ECM monitors the:
- Amplitude of the signal (highest voltage or range sensor is producing)
- Switching time of the signal (how fast from lean to rich)
- Frequency of complete cycles (how many within a period of time)

These characteristics provide info to the ECM that reflect the overall condition of the sensor.

Post Catalytic Converter Sensor Signal

The post catalyst 02 sensors monitor the efficiency of the catalyst as a requirement of OBD II. This signal also provides feedback of the pre-catalyst sensors efficiency and can cause the ECM to "trim" the ms injection time to correct for slight deviations.

Bosch Systems:







- If the catalyst is operating efficiently, most of the remaining oxygen in the exhaust gas is burned (lack of O2 - "constant lean signal").
The sensor signal fluctuates slightly in the higher end of the voltage scale.
- If the post sensor shows excessive fluctuations (which echo the scope pattern of the pre sensor), this indicates that the catalytic converter is not functioning correctly and cannot consume the 02 (fault set).
- If the post sensor fluctuations move out of the normal voltage "window", this indicates that the pre sensor is not performing properly due to slight deterioration. These systems can also "trim" the ms injection time to compensate for this.

The constantly changing oxygen sensor input to the ECM is needed to correct the ms injection time to ensure that the ideal air/fuel ratio is maintained.