Oxygen Sensors and Oxygen Sensor Regulation After Catalytic Converter,Checking

Diagnostic Procedures

Oxygen Sensors and Oxygen Sensor Regulation after Catalytic Converter, Checking

• When servicing terminals 3 and 4 in harness connector of oxygen sensors, use only gold-plated terminals.

Special tools, testers and auxiliary items required

• Hand multimeter (V.A.G 1526) or Multimeter (V.A.G 1715)

• Test adapter kit (V.A.G 1594)

• Wiring diagram

Test Conditions

• Motronic Engine Control Module (ECM) Power Supply Relay (J271) -position 4- must be OK, check:

• Battery voltage (both batteries) must be at least 11.5 Volts.

• All electrical consumers such as, lights and rear window defroster must be switched off.

• For vehicles with automatic transmission, selector lever must be in " P".

• Parking brake must be engaged.

• The Ground (GND) connections between engine and body must be OK.

• Exhaust system must be properly sealed between catalytic converter and cylinder head.

• Coolant temperature must be at least 80 °C => Diagnostic Mode 01 - Read Current System Data, Diagnostic mode 1: Check measured values; PID 5, Coolant temperature.

• Oxygen sensor heaters for oxygen sensors behind catalytic converter must be OK, checking => [ Oxygen Sensor Heaters After Catalytic Converter, Checking ].

• Fuses in right instrument panel fuse holder must be OK:

Right instrument panel fuse holder





Function Test

- Select oxygen sensor test results and check whether specified values are being reached =>Diagnostic Mode 05 - Read Oxygen Sensor Monitoring Test Results, Diagnostic mode 5: Check oxygen sensor test results.

- End diagnosis and switch ignition off.

If specifications are not obtained:

- Check oxygen sensor wires to control module according to wiring diagram.

Checking oxygen sensor wires to control module

Cylinder bank 1

- Connect test box to Engine Control Module (ECM) (J623) wiring harness on connecting test box for wiring test,

Cylinder bank 2

- Connect test box to Engine Control Module (ECM) 2 (J624) wiring harness on connecting test box for wiring test,

Cylinder bank 1 and 2

- Disconnect corresponding 6-pin harness connector to oxygen sensor to be tested: Component location refer to Repair Manual.

• Cylinder bank 1 with cylinders 1 through 6 is located at right in direction of travel.

• Cylinder bank 2 with cylinders 7 through 12 is located at left in direction of travel.

- Check wires between test box and 4-pin connector to Engine Control Module for open circuit according to wiring diagram. Wiring resistance: max. 1.5 ohms









- Check wires for short circuit to B+ and Ground (GND). Specification: infinite ohms

If no malfunction is detected in the wiring:

- Replace respective oxygen sensor:

• Oxygen Sensor (O2S) Behind Three Way Catalytic Converter (TWC) (G130).

• Oxygen Sensor (O2S) 2 Behind Three Way Catalytic Converter (TWC) (G131).

• Oxygen Sensor (O2S) 3 Behind Three Way Catalytic Converter (TWC) (G287).

• Oxygen Sensor (O2S) 4 Behind Three Way Catalytic Converter (TWC) (G288).

- Erase DTC memory of Engine Control Module => [ Diagnostic Mode 04 - Erase DTC Memory ]
Diagnostic Mode 04 - Erase DTC Memory,

- Generate readiness code => [ Readiness Code, Generating ] Monitors, Trips, Drive Cycles and Readiness Codes.