Oxygen Sensor (O2S) Heating Before and After TWC, Checking

Oxygen Sensor (O2S) Heating For HO2S Before And After TWC, Checking

Special tools and equipment






- VAG1526A
- VAG1594A
- VAG1598/31

Test requirements
- Coolant temperature at least 80 degree C.
- Fuse for oxygen sensor heating OK

Test sequence
- Disconnect 4-pin harness connector to oxygen sensor before catalytic converter or
- Disconnect 4-pin harness connector to oxygen sensor behind catalytic converter






- Connect multimeter between terminal 1 and 2 of relevant connector for resistance measurement.
- Specified value at room temperature: 1 to 5 Ohms

NOTE: At higher temperatures, resistance climbs sharply.

If specified value is not obtained:
- Replace Oxygen Sensor (O2S).

If specified value is obtained:
- Check voltage supply of oxygen sensor heating.

Checking voltage supply for oxygen sensor heating






- Connect multimeter between terminal 1 (B+, from Fuel Pump) and 2 (Ground (GND), from ECM) for voltage measurement.
- Start engine.
- Specification: approx. battery voltage, possibly fluctuating

NOTE:
- At certain operating points, the ECM "pulses" the Ground (GND) for oxygen sensor heating. This means that the Ground (GND) is switched on and off at these points. It is therefore possible that the voltage displayed on the tester will fluctuate.
- When the ECM switches oxygen sensor heating on and off it can be observed, if necessary, in the function "Read Measuring Value Block" display group number 041.

If there is no voltage:
- Connect multimeter for voltage measurement as follows:

Harness connector Measure to
Terminal
1 (B+) Vehicle Ground (GND)

- Operate starter briefly.
- Specification: approx. battery voltage

If there is no voltage again:
- Check wire connection from terminal 1 of connector to Fuel Pump (FP) relay via fuse for open circuit:

If voltage supply is OK:






- Connect multimeter for voltage measurement as follows:

Harness connector Measure to
Terminal
2 (Ground -GND- activation of
Engine Control Module -ECM-) B+

- Start engine.
- Specification: approx. battery voltage, possibly fluctuating
- Switch ignition off.

If there is no voltage:
- Connect VAG1598/31 test box at wiring harness to ECM, do not connect ECM.Wiring and Component Testing Using VAG1598/31 Test Box






- Check the following wire connection for open circuit:

Oxygen sensor heater for oxygen sensor before catalytic converter

Harness connector VAG1598/31 test box
Terminal Socket
2 5

Oxygen sensor heater for oxygen sensor behind catalytic converter

Harness connector VAG1598/31 test box
Terminal Socket
2 63

- Repair open circuit if necessary.

If wire connection is OK, but there is no Ground (GND) supply for oxygen sensor heating:
- Replace Engine Control Module (ECM).