Driving Performance Problems After Cold Start

COLD START DRIVEABILITY PROBLEMS, OVERVIEW:
- The time interval between cold start (open loop) and oxygen sensor control (closed-loop), which requires an oxygen sensor temperature of approx. 300°C (572°F), is influenced by the following variables:
^ Ambient temperature (summer/winter).
^ Operating conditions after start.
^ Oxygen sensor heater operation.

- If driveability difficulties occur during cold start, determine whether the problem occurred during the open or closed-loop phase of the start-up as follows (under cold-start conditions):
- Connect VAG 1551 scan tool, refer to Diagnosis with Scan Tool, Address Word 01 Testing and Inspection
.
- Switch ignition ON but do not start engine.
- Select "Read Measuring Value Block" function 08 and advance until display shows "Read measuring value block 10".

- Indicated on display:

Read measuring value block 10
1 2 0.4V 0.4V

- Display fields 3 and 4 show signal voltage for oxygen sensors before the three way catalytic converters (vehicle cold; oxygen sensor control does not function; values = 0.350 to 0.450 volts).

WARNING: Use a second technician to operate the VAG 1551 scan tool.

- Start engine (without previously switching ignition off), drive and record voltage signal (display field 3 shows bank 1; display field 4 shows bank 2).
^ When oxygen sensor control starts, the voltage signal fluctuates between 0.0 and 0.9 volts (the voltage signals of both banks do not need to be synchronous with one another).
^ If driveability difficulties occur before the start of oxygen sensor control, oxygen sensor control can not be the cause of the problem.
^ If driveability difficulties occur after the start of oxygen sensor control, check function of heated oxygen sensor.
^ If driveability improves after the start of closed-loop oxygen sensor control, the cause (e.g. air leak, faulty fuel injector) works against the improvement by interrupting control. This can be recognized by reading the oxygen sensor learned values, function 08, display group 005 or 006.

NOTE: For troubleshooting driveability problems, oxygen sensor control can be programmed to switch ON or OFF using display group 099. By pushing buttons -4- and -8- on the VAG 1551 scan tool (selecting between "Basic Setting function 04 and "Read Measuring Value Block" function 08), oxygen sensor control can be switched ON and OFF.