Sensor and Control Check
Heated Oxygen Sensor (HO2S) and oxygen sensor control behind Three Way Catalytic Converter (TWC), checking
- V.A.G 1551 scan tool (or VAG 1552 mobile scan tool) with VAG 1551/3B cable
- VAG 1598/31 adapter cable
- VAG 1788/10 RPM adjuster
- VAG 1526 multimeter or VAG 1715 multimeter
- VAG 1594 connector test kit
- Wiring diagram
Test requirements
- Exhaust system must be properly sealed between catalytic converter and cylinder head.
- Coolant temperature must be at least 85 °C, See display group 04, display field 3
Function test
- Connect V.A.G 1551 scan tool (VAG 1552). Start engine and select the Engine Control Module (ECM) using address word 01. (connecting scan tool and selecting ECM). Refer to "Scan Tool Testing/Scan Tool Connecting and Initial Checks/Connecting VAG 1551 Scan Tool", Testing and Inspection
Indicated on display:
Rapid data transfer HELP
Select function XX
- Press buttons -0- and -8- to select "Read measuring value block" function 08. Press -Q- button to confirm input.
Indicated on display:
Read measuring value block
Enter display group number XXX
- Press buttons -0-, -3- and -4- to select "Display group number 34". Press -Q- button to confirm input.
Indicated on display: (1 to 4 - display fields)
Read measuring value block 34 ->
1 2 3 4
- Use VAG 1788/10 RPM adjuster to adjust engine RPM to between 1800 and 2200 RPM:
- Hold engine speed between 1800 and 2200 RPM until catalytic converter temperature in display field 2 rises to between 350 and 500 °C.
NOTE: This process can take a few minutes.
- Press -C- button.
Indicated on display:
Read measuring value block
Enter display group number XXX
- Press buttons -0-, -3- and -0- to select "Display group number 30". Press -Q- button to confirm input.
Indicated on display: (1 to 4 = display fields)
Read measuring value block 30 ->
1 2 3 4
- Check operational condition of oxygen sensor control behind catalytic converter (display field 2): Specification: x 1 x
NOTE: The bits in display fields 2 are only set to 1 after catalytic converter temperature has risen to above 350 °C (See display group 34, display field 2).
The sensor heater is pulsed by the Engine Control Module (ECM). This is why the indication for the sensor heater alternates between 0 and 1.
Explanation of 3-digit value in display field 2:
If oxygen sensor heater is not active:
- Test oxygen sensor heater after catalytic converter. Heater Check
If oxygen sensor or oxygen sensor control is not active:
- Check primary voltage.
NOTE: Oxygen sensor control is not active for engine code AWM.
If specified value is obtained:
- Change to display group 37 as follows:
- Press -C- button.
- Press buttons -0-, -3- and -7- to select "Display group number 37". Press -Q- button to confirm input.
Indicated on display: (1 to 4 = display fields)
Read measuring value block 37 ->
1 2 3 4
- Check dwell time of oxygen sensor control before catalytic converter in display field 3:
Specification: -150 to 150 ms and the diagnostic result in display field 4:
Specification: Sys. OK
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 -1- by holding oxygen sensor control before catalytic converter -2- at its higher or lower point for a specific time (dwell time) -3-. 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.
- Check oxygen sensor voltage in display field 2: Specification: 0 to 1 volt (may oscillate slightly)
If indication in display field 2 remains constant on one value:
- Continue testing according to the following table.
If Syst OK is indicated in display field 4 and the indicated value in display field 3 is above 200 ms:
- Check whether exhaust system is properly sealed.
If Syst not OK is indicated in display field 4 and the indicated value in display field 3 is above 800 ms:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
- Perform a road test to free the Heated Oxygen Sensor (HO2S) of any possible residue, and repeat the test.
Observe the safety precautions that apply to road tests.
If specified values are not obtained again:
- Replace Oxygen Sensor (O2S) behind Three Way Catalytic Converter (TWC) - G130-.
NOTE: If oxygen sensor voltage is OK and dwell time of oxygen sensor control behind catalytic converter is still above 150 ms, even after a road test, this suggests aging of an oxygen sensor before catalytic converter.