HO2S sensor are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature.
The ME engine controller commands the heater ON or OFF to maintain a specific HO2S operating temperature range. The ME engine controller monitors the voltage on the HO2S heater low control circuit for heater fault diagnosis.
Removal & Installation
M112 & M113 Engines
- Before servicing the vehicle, refer to the precautions.
- Raise and safely support the vehicle securely on jackstands.
- Remove rear section of lower engine compartment paneling.
- Unclip electrical connector and electrical feed line for corresponding O2 sensor out of retaining clamps on transmission.
- Remove heat shield for steering below left catalytic converter.
- Disconnect electrical connector for corresponding O2 sensor.
- Remove complete exhaust system.
Unscrew corresponding O2 sensor out of catalytic converter completely
- Installation is the reverse of removal.
- Apply heat-resistant lubricant to thread of O2 sensor.
- Tighten O2 sensor to 37 ft. lbs. (50 Nm).
- Connect STAR DIAGNOSIS, or equivalent scan tool and read out fault memory.
All Mercedes Benz electronic testing is performed by reading the fault memory of ME control unit and if necessary, working through test schedules contained in the STAR DIAGNOSIS tool.