WIS 07.61 Gasoline Engine and Injection System ME

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Heated Oxygen Sensors (HO2S) - Gasoline Engine and Injection System

Description - Heated Oxygen Sensors (HO2S)

The Heated Oxygen Sensors (HO2S) are commonly known as O2 Sensors or Lambda Sensors. They are used to monitor, in real time, whether the air–fuel ratio of a combustion engine is rich or lean.

They work by producing 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.

http://en.wikipedia.org/wiki/Oxygen_sensor

Location - Heated Oxygen Sensors (HO2S)

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

Issues - Heated Oxygen Sensors (HO2S)

HO2S have a limited lifetime, typically 160,000 Km (100,000 miles).

Symptoms of a failing HO2S include:

• Warning light on dash,
• Increased tailpipe emissions,
• Increased fuel consumption,
• Hesitation on acceleration,
• Stalling,
• Rough idling.

Heating Element Failure

The HO2S contains a heating element which often fails by going open circuit. The resistance of a typical W220 heater element has been measured as 9.2 Ohms. The specified heater resistance is TBD.

Resulting Fault Codes are:

• 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)

Cable Lengths

The W220 HO2S are electrically interchangeable but have different cable 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.

Contamination

Contamination of the oxygen sensor can result from the use of an inappropriate RTV or silicon sealer (not oxygen sensor safe) or excessive engine coolant or oil consumption.

• To check 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 drive-ability problem.
• Eliminate the source of contamination before replacing the oxygen sensor.

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]

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

Fuel Injectors - Gasoline Engine and Injection System

Description - Fuel Injectors

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