Oxygen Sensor Control After Catalytic Converter, Checking

Heated Oxygen Sensor (HO2S) And Oxygen Sensor Control After Three Way Catalytic Converter (TWC), Checking


NOTE: Oxygen sensor control behind catalytic converter is superior to oxygen sensor control before catalytic converter and is responsible for control correction.







It corrects slight changes in the mixture (i.e. enrichment) via the oxygen sensor before catalytic converter by holding oxygen sensor control before catalytic converter at its higher or lower point for a specific time (dwell time). If this time is in the positive range (i.e. 50 ms), mixture is shifted in the -enrich- direction. If it is in the negative range (e.g. -50 ms), mixture will be shifted in the -lean- direction.







Special tools and equipment
- VAG1594A
- VAG1598/31
- VAG1788/10 RPM adjuster
- VAS5051 with VAG5051/1
- or
- VAG1551 with VAG1551/3A

Test requirements:
- Road test performed and DTC memory erased.
- Coolant Temperature at least 80 °C.

Test sequence
- Connect VAS5051 tester or VAG1551 scan tool and select control module for engine electronics using "address word" 01. Engine must run at idle. [1][2]Scan Tool Connecting and Initial Checks

When indicated on display


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -4- to select "Initiate basic setting" and press -Q- button to confirm input.


NOTE: During basic setting, the Evaporative Emission (EVAP) canister purge regulator valve (EVAP valve -N80-) is closed and the A/C compressor is switched off


When indicated on display


Basic Setting Q
Enter display group number XXX


- Press buttons -0-, -3- and -4- to select "display group number 034" and press -Q- button to confirm input.

When indicated on display


System in basic setting 34 ->
1 2 3 4


- Use VAG1788/10 RPM adjuster to adjust engine speed to between 2800 and 3200 RPM.
- Continue test as soon as display field 2 indicates an exhaust temperature of more than 350 °C.


NOTE: This process can take a few minutes.


- Press -C- button.
- Use VAG1788/10 RPM adjuster to adjust engine speed to between 1800 and 2200 RPM.

When indicated on display


Basic Setting Q
Enter display group number XXX


- Press buttons -0-, -3- and -0- to select "display group number 030" and press -Q- button to confirm input.

When indicated on display


System in basic setting 30 ->
1 2 3 4


- Check oxygen sensor status for oxygen sensor behind catalytic converter in display field 2.


NOTE: "Oxygen sensor status" indicates status of oxygen sensor control and oxygen sensor

Display Group 030: