Heater Check

Heated Oxygen Sensors (HO2S) Before Catalytic Converter, Checking Heating







Special tools and equipment
- VAG 1526A
- VAG 1594A
- VAG 1598/31

Test requirements:
- Fuse for oxygen sensor heating OK

Test sequence
- Disconnect 6-pin connector of bank 1, heated oxygen sensor (HO2S) -G39- before catalytic converter.







- 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- before catalytic converter -G39-.

If specified value is obtained:

Check voltage supply for heated oxygen sensor (HO2S) heating







- Connect multimeter between terminals 3 and 4 to measure voltage.
- Start engine.
- Specified value: approx. battery voltage

NOTE: Points at which heating oxygen sensor (HO2S) 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.

If no voltage is present:
- Connect multimeter as follows to measure voltage.

Connector Measure to
terminal
3 Engine ground

- Operate starter briefly.
- Specified value: approx. battery voltage

If no voltage is present:
- Check wiring from terminal 3 on the connector via fuse to fuel pump relay for an open circuit:

If voltage supply is OK:
- Connect multimeter as follows to measure voltage:

Connector Measure to
terminal
4 (Ground activation Battery positive
by engine control module)

- Start engine.
- Specified value: approx. battery voltage

NOTE: Points at which heating oxygen sensor (HO2S) 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 VAG 1598/31 to wiring harness for engine control module; do not connect engine control module. Wiring and Component Testing Using VAG1598/31 Test Box
- Check for open circuit in following wiring connections:

Connector Test box VAG 1598/31
terminal Socket
4 5

- Repair open circuit, if necessary.

If wiring is OK but there is no Ground supply for the heating oxygen sensor (HO2S) heating:
- Replace engine control module.