Oxygen Sensor Checking With "Read Measuring Value Block"

CHECKING HEATED OXYGEN SENSOR SIGNAL VOLTAGE

^ Connect VAG 1551 and/or VAG 1552 scan tool and advance through program sequence until "Select function XX" is displayed. Display will appear as shown:

Rapid data transfer HELP
Select function XX

^ Press buttons 0 and 8 to select "Read Measuring Value Block" function 08. Display will appear as shown:

Rapid data transfer Q
08- Read Measuring Value Block

^ Press Q button to confirm input. Display will appear as shown:

mRead measuring value block HELP
Input display group number XXX

^ Press buttons 0, 0 and 1 to input display group 00. Display will appear as shown:

1mRead measuring value block Q
Input display group number 001

^ Press Q button to confirm input. Display will appear as shown:

Read measuring value block 1
1 2 3 4

- Do not continue with the test until display value 1 (engine coolant temperature ) is 80°C (176°F) minimum.

^ Press C button.
^ Press buttons 0, 1 and 0 to input display group 010.
^ Press Q button to confirm input. Display will appear as shown:

Read measuring value block 10
1 2 3 4

Signal voltage for each of the two oxygen sensors is displayed in display fields 3 and 4.

If sensor voltage fluctuates very slowly:
- Check oxygen sensor heating.

If no sensor voltage is displayed, signal wire is interrupted:
- Check wiring connection, (malfunction stored in DTC memory).
^ If a constant voltage of 0.0 - 0.3 volts is displayed, a lean mixture is measured by the oxygen sensor.
^ If a constant voltage of 0.7 - 0.9 volts is displayed, a rich mixture is measured by the oxygen sensor.
- Display will appear as shown:

Read measuring value block Q
Input display group number XXX

Checking HO2S Learning Values

When functioning properly, the most recent oxygen sensor values are checked first. Various malfunctions (e.g. intake air leak, faulty fuel injector) result in a modified mixture ratio. This is recognized by oxygen sensor control and is compensated for by an adaption to the specified injection times stored in the map. Injection times that deviate from injection specifications indicate a possible malfunction. There is a deviation according to idle and various partial load ranges. These deviations are shown in display groups 005 (bank 1) and/or 006 (bank 2). The deviations of the injection times are specified in % of the specified values stored in the map.
^ Positive learning value (+%): mixture too lean, more fuel required.
^ Negative learning value (-%): mixture too rich, less fuel required.

Possible causes for these learning values are listed in display groups 005 and 006 in the malfunction repair column.
- Press buttons 0, 0 and 5for display group 005 (bank 1), or buttons 0, 0 and 6 for display group 006 (bank 2), and in either case:
- Press Q button to confirm input. Display will appear as shown:

Read measuring value block 5
-4.6% 0.7% 0 0

- Depending on whether high or low oxygen sensor learning values are displayed, proceed according to "Corrective steps" column of table for corresponding display group.

NOTE: If necessary for troubleshooting, the measuring value blocks can also be displayed and printed using the "Basic Setting" function 04 (e.g. oxygen sensor learning values). With this function the EVAP canister influence, among other things, is eliminated.