Oxygen Sensor After Catalyst Checking
Oxygen Sensor and Oxygen Sensor Control Behind Catalytic Converter, Checking
Test equipment and shop tools
- Fluke 83 (or equivalent)
- VAG1594 A
- VAG1598/31
- VAG1788/10
- VAS5051 with VAS5051 /1
- or
- VAG1551 with VAG1551/3B
NOTE:
- Oxygen sensor control behind the catalytic converter is responsible for final control connection. It is the primary sensor and can override the signal from the oxygen sensor control before the catalytic converter.
- It corrects slight changes in the mixture (i.e. enrichment) via the oxygen sensor before catalytic converter by holding the oxygen sensor control before catalytic converter at its higher or lower limit for a specific time (duration). If this time is in the positive range (i.e. 50 ms), mixture is shifted in the -enrich- direction. If this time is in the negative range (i.e. -50 ms), mixture is shifted in the -lean- direction.
Test conditions
- Perform road test and do not erase DTC memory.
- Coolant temperature at least 85 °C (185 °F) (Display group 004, display field 3)
- Connect vehicle diagnostic, testing and information system VAS5051 or VAG1551 scan tool and select engine electronics control module by entering address word "01". When doing this the engine must be at idle. Refer to " Scan Tool Testing/Scan Tool Connecting and Initial Checks/Connecting VAS 5051/ VAG 1551 Scan Tool" Testing and Inspection
Indicated on display
Rapid data transfer HELP
Select function XX
- Press buttons -0- and -4- to select function "Basic Setting" and confirm entry with -Q- button.
NOTE: During the basic setting the Evaporative Emission (EVAP) canister purge regulator valve -N80 is closed and the A/C compressor is switched off
Indicated on display
Basic Setting
Input display group number XXX
- Press buttons -0-, -3- and -4- to select "display group number 034" and confirm entry with -Q- button.
When indicated on display:
System in Basic Setting 34 ->
1 2 3 4
- Adjust engine speed using
VAG1788/10 to 2800 - 3200 RPM.
- Continue test as soon as display field 2 indicates an exhaust temperature of more than 320 °C.
NOTE:
This process can take a few minutes.
- Press -C- button.
- Adjust engine speed using
VAG1788/10 to 1900 - 2200 RPM.
When indicated on display:
Basic Setting Q
Input 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 "indicate status of oxygen sensor control and oxygen sensor.
Display Group 030:
Significance of 3 digit indication in Display Group 030
If the specified value of "B1-S2 OK" is reached:
- Press-C-button.
When indicated on display
Basic Setting Q
Input display group number XXX
Test requirements
- Engine runs at 1900 - 2200 RPM
When indicated on display
System in Basic Setting 43 ->
1 2 3 4
- Check specified value in display field 4.
Display Group 043:
If specified value of "B1-S2 OK" is reached:
- Press -C- button.
Test Requirements
- Engine runs at 1900 - 2200 RPM
- Press buttons -0-, -4- and -4- to select 11display group number 044" and press -Q- button to confirm input.
Display Group 044:
If the specified value of "B2-S2 OK" is reached:
- Press-C-button.
Checking oxygen sensor control behind catalytic converter
- Carry out road test for approx.:10 minutes.
Indicated on display
Basic Setting Q
Input display group number XXX
- Press buttons -0-, -3- and -7- to select "display group number 037" and press -Q- button to confirm input.
Indicated on display
System in Basic Setting 37 ->
1 2 3 4
- Check oxygen sensor voltage in display field 2
- Check dwell time (hold up) between oxygen sensor 1 before catalytic converter and oxygen sensor 2 behind catalytic converter in display field 3 and diagnostic result in display field 4.
Display Group 037:
- Press -C- button.
- Press buttons -0-, -3- and -8- to select "display group number 038" and press -Q- button to confirm input.
Indicated on display: (1 - 4 = display fields)
System in Basic Setting 38 ->
1 2 3 4
Display Group 038:
Evaluation display group 037 and 038
Continuation
If the specified value in display group 037 and 038, display 3 or 4 is not obtained:
- Check exhaust system and catalytic converter for leaks (check clamps and exhaust for damage)
- If the difference of the values in measuring blocks, display fields 3 (oxygen sensor correction value) is to large (e.g. +500 ms, - 500 ms), it is possible that the oxygen sensor are interchanged (mixed up).
If none of the causes are identified:
- Replace particular oxygen sensor "before" catalytic converter.