Heater Check

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







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

Test requirements:
- Fuse for heated oxygen sensor (HO2S) heating OK.

Test sequence
- Disconnect 4-pin connector of relevant heated oxygen sensor (HO2S) behind catalytic converter.







- Connect multimeter between terminals 1 and 2 to measure resistance.
- Specified value at room temperature 6.4 to 47.5 Ohms

If specified value is not obtained:
- Replace relevant heated oxygen sensor (HO2S) behind catalytic converter.

If specified value is obtained:

Check voltage supply for heated oxygen sensor (HO2S) heating







- Connect multimeter between terminals 1 (positive) and 2 (Ground) to measure voltage.
- Start engine.
- Specified value: approx. battery voltage

NOTE: Points at which heated 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 4.

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

Connector Measure to
terminal
1 Engine ground

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

If no voltage is present:
- Check wiring from terminal 1 on 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
2 (ground activation Battery positive
by engine control module)

- Start engine.
- Specified value: approx. battery voltage, may fluctuate
- 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:
- Heated oxygen sensor (HO2S) heating -729- Bank 1 behind TWC:

Connector Test box VAG 1598/31
terminal Socket
2 63

- Heated oxygen sensor (HO2S) heating -720- Bank 2 behind TWC:

Connector Test box VAG 1598/31
terminal Socket
2 6

- Repair open circuit, if necessary.

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