Manufacturer's Scan Tool

Oxygen Sensor Heater before Catalytic Converter, Checking

Special tools, testers and auxiliary items required

• Multimeter (V.A.G 1526 A)

• Connector test kit (V.A.G 1594 A)

• Test box (VAG1598/31)

Requirements

• Coolant temperature at least 80 °C

• Fuse for Oxygen Sensor (O2S) heating OK.



Work sequence

- Disconnect 6-pin connector (black) - 5 - to Oxygen Sensor before Three Way Catalytic Converter (TWC).





• To gain access to the connector, remove coolant expansion tank bolt (arrow) and move expansion tank to side. Fuel hoses remain connected.





- Connect multimeter between terminals 3 and 4 to measure resistance.





• Specified value at room temperature 2.5 to 10 ohms

If specified value is not obtained:

- Replace Heated Oxygen Sensor (HO2S) (G39).

If specified value is obtained:

Checking voltage supply for Oxygen Sensor heating

- Connect multimeter between terminals 3 and 4 to measure voltage.





- Start engine.

• Specified value: Approx. battery voltage (B+)

• Points at which Oxygen Sensor heating is switched on and off by Engine Control Module (ECM) can be observed in "Reading measured value block " function, display group number 041 and display zone 2.

If no voltage is present:

- Connect multimeter as follows to measure voltage.









- Operate starter briefly.

• Specified value: Approx. battery voltage (B+)

If no voltage is present:

- Check wiring from terminal 3 on the connector via the fuse to fuel pump relay for an open circuit.

If voltage supply is OK:

- Connect multimeter as follows to measure voltage:









- Start engine.

• Specified value: Approx. battery voltage (B+)

• Points at which Oxygen Sensor heating is switched on and off by engine control module can be observed in "Reading measured value block" function, display group number 041 and display zone 2.

- Switch ignition off.

If no voltage is present:

- Connect test box (VAG1598/31) to wiring harness for engine control module; do not connect directly to ECM. Refer to => [ Electrical Testing, with Test Box VAG 1598/31 ] Electrical Testing, With Test Box VAG 1598/31.

- Check for open circuit in following wiring connections:









- Repair open circuit, if necessary.

If wiring is OK but there is no ground for the Oxygen Sensor heating:

- Replace ECM. Refer to => [ Engine Control Module without Metal Anti-Theft Housing, Replacing ] Engine Control Module Without Metal Anti-Theft Housing, Replacing.