WIS 07.61 Gasoline Engine and Injection System ME

W220 Heated Oxygen Sensors (HO2S) or Lambda Sensors

Description - Heated Oxygen Sensors (HO2S)

• G3/3 Left and G3/4 Right are the Heated Oxygen Sensors before or upstream of the TWC (KAT).
• G3/5 Left and G3/6 Right are the Heated Oxygen Sensors after or downstream of the TWC (KAT).

How It Works - Heated Oxygen Sensors (HO2S)

The Heated Oxygen Sensor (HO2S) or Lambda Sensor produces a voltage from approximately 1.0 V during rich operating conditions to 0.01 V (10 mV) during lean operating conditions. The HO2S is like an open circuit and produces no voltage when it is below 360C (600F).

The powertrain control module (PCM) supplies a bias voltage of about 450 mV between the heated oxygen sensor (HO2S) high signal and low signal circuits. The HO2S varies the voltage within a range of about 1,000 mV when the exhaust is rich, down through about 10 mV when exhaust is lean. The PCM constantly monitors the HO2S signal during Closed Loop operation and compensates for a rich or lean condition by decreasing or increasing the fuel injector pulse width as necessary. If the HO2S voltage remains at or near the 450 mV bias for an extended period of time, P0154 diagnostic trouble code (DTC) will be set.

Resistance of Heater - Heated Oxygen Sensors (HO2S)

• Measured as 9.2 Ohms, specified value TBD.

Heated Oxygen Sensor Cable Lengths - Heated Oxygen Sensors (HO2S)

Note two different lengths.

• G3/3 Left and G3/4 Right Front or Upstream HO2S (Long Cable). Wire length: 440mm (17.3 inches) sensor washer to end of connector. Total length: 460mm.
• G3/5 Left and G3/6 Right Rear or Downstream HO2S (Short Cable). Wire length: 322mm (12.7 inches) sensor washer to end of connector. Total length: 340mm.

Connector Pin Diagram - Heated Oxygen Sensors (HO2S)

HO2S Wire Colours

• Pin 1 White Heater
• Pin 2 White Heater
• Pin 3 Grey O2 Sensor Low
• Pin 4 Black O2 Sensor High

HO2S Connector to Power Control Module (N3/10) Cable Wire Colours

• Pin 1 Red or Red/Green Heater Ground
• Pin 2 Brown or Brown/Black Heater +12V
• Pin 3 Green O2 Sensor Low
• Pin 4 Black O2 Sensor High

Electrical Wiring Diagram HO2S Upstream of TWC [KAT]

Fault Codes - Heated Oxygen Sensors (HO2S)

• P20BF-004 G3/3 Left HO2S before TWC (KAT) open circuit in sensor heater line (P0156)
• P2082-004 G3/3 Left HO2S before TWC (KAT) open circuit (P0154)

Contamination Note

Contamination of the oxygen sensor can result from the use of an inappropriate RTV sealant (not oxygen sensor safe) or excessive engine coolant or oil consumption. Remove the HO2S and visually inspect the portion of the sensor exposed to the exhaust stream in order to check for contamination. If contaminated, the portion of the sensor exposed to the exhaust stream will have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Eliminate the source of contamination before replacing the oxygen sensor.

DIY Articles - Heated Oxygen Sensors (HO2S)

http://www.benzworld.org/forums/w203-c-class/1474361-p0154-code-wont-go-away.html

http://www.benzworld.org/forums/w203-c-class/1474361-p0154-code-wont-go-away-2.html

http://www.hotrodlane.cc/New%20LS%20Links%20Page/LS%20trouble%20codes/DTC%20P0154.htm