O2S Control, Checking Before Three Way Catalytic Converter

NOTE:
- G39 = Heated Oxygen Sensor (HO2S), bank 1
- G108 = Heated Oxygen Sensor (HO2S) 2, bank 2


- Read measuring value block using VAG 1551 scan tool until display shows "Read measuring value block 1" (display group 001).

Indicated on display


Read measuring value block 1 ->
1 2 3 4


NOTE: Continue with the test only if the value in display field 1 (engine coolant temperature) is at least 80 °C (176 °F).


- Press -C- button.
- Press buttons -0-, -1- and -0- to input display group 010.
- Press -Q- button to confirm input.

Indicated on display


Read measuring value block 10 ->
1 2 3 4


Display fields 3 and 4 show the signal voltages of both heated oxygen sensors.

If sensor voltage fluctuates very slowly, Oxygen Sensor (O2S) Control, Checking

If a constant sensor voltage of 0.000 V is displayed, there is a short to Ground (GND).
- Check DTC memory.

If sensor voltage is constant between 0.350 and 0.450 volts, the signal is interrupted:
- Check DTC memory.

If sensor voltage is a constant 2.550 volts, there is a short to battery positive voltage (B+):
- Check DTC memory.
- If sensor voltage is a constant 0.0 to 0.3 volts, the oxygen sensor measures a lean mixture:
- Check DTC memory.
- If sensor voltage is a constant 0.6 to 0.9 volts, the oxygen sensor measures a rich mixture:
- Check DTC memory.
- Press -C- button.

Indicated on display


Read measuring value block Q
Input display group number xxx


With a properly functioning oxygen sensor, the actual control learning values can be checked.

Various malfunctions (e.g. intake air leakage, faulty fuel injectors etc.) can cause a change in the mixture composition. These malfunctions are recognized by the oxygen sensor and are corrected via oxygen sensor control by adjusting the fuel injection time via the ECM. Fuel injection time that deviates from the programmed basic fuel injection time indicates a malfunction of some type.

These deviations are shown (oxygen sensor control learned values) in display group 005 (bank 1) or 006 (bank 2). There is a deviation between idle and partial load readings; the deviation between actual fuel injection times and the programmed basic settings are indicated as a percentage (%).

Positive oxygen sensor control learned values (+%):
Programmed basic fuel injection time too short (mixture too lean), actual fuel injection time by ...% longer, so that Lambda=1 can be obtained.

Negative oxygen sensor control learned value (-%):
Programmed basic fuel injection time too long (mixture too rich) , actual fuel injection time by ...% shorter, so that Lambda=1 can be obtained.

- Press buttons -0-, -0- and -5- to input display group number 005 for bank 1 or press buttons -0-, -0- and -6- to input display group number 006 for bank 2.
- Press -Q- button to confirm input.

Indicated on display (example)


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


NOTE: If necessary, display group 005 (bank 1) or 006 (bank 2) for troubleshooting can be read using "Basic Setting" function 04 and then printed out, By selecting this function (among other things) the evaporative emissions factor is not included. refer to "Basic Setting (Function 04)". Basic Setting (Function 04)