Oxygen Sensor O2S 3 Heater Behind Catalytic Converter, Checking

Observe all safety precautions: SAFETY PRECAUTIONS 

View clean working conditions: CLEAN WORKING CONDITIONS 

Use only gold-plated terminals when servicing any component with gold-plated electrical harness connector terminals.

For wiring diagrams, component locations, and connector views, Refer to the applicable wiring diagram.

Special tools and workshop equipment required 

• multimeter.
• Wiring diagram.

Test requirements 

• Fuse -SB21- OK.
• Battery voltage at least 12.5 volts.
• All electrical consumers such as, lights and rear window defroster, switched off.
• Vehicles with automatic transmission, shift selector lever into position "P" or "N".
• A/C switched off.
• Ground (GND) connections between engine/transmission/chassis OK.
• Ignition switched off.

Test procedure 

-- Perform a preliminary check to verify the customers complaint. Refer to PRELIMINARY CHECK .

Start diagnosis 

-- Remove right cover from vehicle underbody. Refer to the appropriate service information.

Checking internal resistance

-- Disconnect the Oxygen Sensor (O2S) 3 Behind Three Way Catalytic Converter (TWC) -G287- electrical harness connector -1-.

-- Using a multimeter, check the Oxygen Sensor (O2S) 3 Behind Three Way Catalytic Converter (TWC) -G287- terminals 1 to 2 for resistance.

Specified value: 2.5 to 14.0 Ω (at approx. 20 °C)

If the specification was not obtained:

-- Replace the Oxygen Sensor (O2S) 3 Behind Three Way Catalytic Converter (TWC) -G287-. Refer to the appropriate service information.

If the specification was obtained:

Checking voltage supply 

-- Using a multimeter, check the Oxygen Sensor (O2S) 3 Behind Three Way Catalytic Converter (TWC) -G287- electrical harness connector terminal 1 to ground (GND) for voltage.

Specified value: Battery voltage.

If the specification was not obtained:

-- Check the Oxygen Sensor (O2S) 3 Behind Three Way Catalytic Converter (TWC) -G287- electrical harness connector terminal 1 to the Motronic Engine Control Module (ECM) Power Supply Relay -J271- socket 2/87 an open circuit, a short circuit to each other, or Ground (GND).

-- Check the electrical harness connector for damage, corrosion, loose or broken terminals.

-- If necessary, repair the faulty wiring connection.

If the specification was obtained:

Checking Ground (GND) activation 

If the manufacturers test box is being used, perform the following step.

-- Install the test box.

If the manufacturers test box is not being used, perform the following step.

-- Remove the Engine Control Module (ECM) -J623-. Refer to the appropriate service information.

-- Using a multimeter, check the Oxygen Sensor (O2S) 3 Behind Three Way Catalytic Converter (TWC) -G287- electrical harness connector to the Engine Control Module (ECM) -J623- electrical harness connector T94 for resistance.

Oxygen Sensor (O2S) 3 Behind Three Way Catalytic Converter (TWC) -G287- electrical harness connector terminal	Engine Control Module (ECM) -J623- electrical connector T94 terminal or test box socket
2	7

Specified value: 1.5 Ω max.

If the specification was not obtained:

-- Check the wiring for a open circuit or short to Ground (GND).

-- Check the electrical harness connector for damage, corrosion, loose or broken terminals.

-- If necessary, repair the faulty wiring connection.

If no malfunction is detected in the wiring and if the voltage supply was OK:

-- Erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY 

-- Perform a road test to verify repair.

If the DTC does not return:

Generate readiness code. Refer to READINESS CODE .

If the DTC does return and no malfunction is detected in the wiring and the voltage supply was OK:

-- Replace the Engine Control Module (ECM) -J623-. Refer to the appropriate service information.

Final procedures 

After repair work, the following work steps must be performed in the following sequence:

1. Check the DTC memory. Refer to DIAGNOSTIC MODE 03 - READ DTC MEMORY .
2. If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
3. If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .