Driving Performance Problems After Cold Start

START OF OPERATION
The amount of time that elapses until oxygen sensor control begins, when the sensor reaches the required temperature of approximately 300°C (572°F), is mainly influenced by the following factors:
^ Ambient temperature (summer/winter).
^ Operating conditions after start.
^ Oxygen sensor heater operation.

MALFUNCTIONS
If malfunctions occur after the cold start, check whether the problem occurs before or only after control begins:
- Check vehicle under cold start conditions.
- Switch ignition ON but do not start the engine.
- Connect VAG 1551 scan tool. Refer to Connecting and Operating VAG Scan Tool
- Advance through program sequence until display shows "Select function XX". 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:

Rapid data transfer HELP
Input display group number XXX

- Press buttons 0, 1 and 0 to select display group 010. Display will appear as shown:

Read measuring value block Q
Input display group number 010

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

Read measuring value block 1
1 2 0.4V 0.4V

Signal voltage for each of the two oxygen sensors is displayed in display fields 3 and 4 (e.g. vehicle cold/O2S control not operating = 0.4 volts).

WARNING!:
For testing during a road test, the scan tool must be operated by a second technician.
Do not allow ignition to be switched OFF before driving.
- Start engine, drive vehicle and observe voltage signal.
^ Display field 3: Cylinder bank 1.
^ Display field 4: Cylinder bank 2.

When O2S control begins, the voltage signal starts to fluctuate between 0.0 - 0.8 volts.
- Voltage signals for the two cylinder banks must not be synchronous with each other.

Display will appear as shown:

Read measuring value block 1
1 2 0.72V 0.19V

- Voltage greater than 0.4 volts: rich mixture.
- Voltage less than 0.4 volts: lean mixture.

Does the driving performance complaint only occur after control starts (fluctuation of the voltage values around the average of 0.4 volts).

- If yes, oxygen sensor control is a possible cause:
^ Check O2S control function.
- If not, oxygen sensor control does not cause the malfunction condition.

NOTE:
If the malfunction condition improves after oxygen sensor control begins, troubleshooting (e.g. intake air leak, faulty fuel injector) will be hampered by the control phase when it begins. This can be observed. e.g. by displaying the oxygen sensor learning values. Proceed as follows:
^ Select and read out display groups 005 (bank 1) and/or 006 (bank 2) using "Read Measuring Value Block" function 08. If deviations are found, repair using the procedures described with display groups 005 and 006.
^ If necessary, the measuring value blocks can also be read and printed out using "Basic Setting" function 04 (e.g. oxygen sensor learning values). In this function, EVAP canister influence, among other things, is eliminated.