Oxygen Sensors and Oxygen Sensor Regulation Before Catalytic Converter, Checking

Diagnostic Procedures

Oxygen Sensors and Oxygen Sensor Regulation Before Catalytic Converter, Checking

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

Special tools, testers and auxiliary items required

• Multimeter (VAG1526) or Multimeter (VAG1715)

• Connector test kit (VAG1594)

• Wiring diagram

Test requirements

• Fuses in E-box (plenum chamber, left) must be OK:





• Motronic Engine Control Module (ECM) Power Supply Relay 2 (J670) must be OK, check:

• Battery voltage must be at least 11.5 volts.

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

• Parking brake must be engaged or else daylight driving lights will be switched on.

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

• If vehicle is equipped with an A/C system, it must be switched off.

• Ground (GND) connections between engine and chassis 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 1: Check measured values; PID 5, Coolant temperature.

• Oxygen sensor heater for oxygen sensor before catalytic converter must be OK, check.

Function test

- Select the lambda test results and check whether the specified values are being reached , Diagnostic mode 5: Check output of oxygen sensor signals.

- End diagnosis and switch ignition off.

If specified values are not obtained:

- Test oxygen sensor wires according to wiring diagram.

Checking oxygen sensor wires

- Connect test box to control module wiring harness , connect test box for wiring test.

- Disconnect 6-pin harness connector to the respective oxygen sensor:





• Heated Oxygen Sensor (HO2S) (G39), bank 1, 6-pin harness connector - 1 -,

• Heated Oxygen Sensor (HO2S) 2 (G108), bank 2, 6-pin harness connector - 4 -.

- Check wires between test box and 6-pin connector to Engine Control Module (ECM) for open circuit according to wiring diagram.





Wire resistance: max. 1.5 ohms





- Check wires for short circuit to B+ or Ground (GND).

Specified value: infinite ohms

If no malfunctions are found in wires:

- Replace the respective oxygen sensor:

• Heated Oxygen Sensor (HO2S) (G39) bank 1 ,

• Oxygen Sensor (O2S) 2 Behind Three Way Catalytic Converter (TWC) (G108).

Final Procedures

After the 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 ] Diagnostic Modes 01 - 09.

2. If necessary, erase the DTC memory. Refer to --> [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09.

3. If the DTC memory was erased, generate readiness code. Refer to --> [ Readiness Code ] Readiness Code.