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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
Proper function of the oxygen sensor heater
If driveability difficulties occur during cold start,
determine whether the problem occurred during
the open- or closed-loop phase of the startup as
follows (under cold-start conditions):
- Connect VAG 1551 scan tool Repair Group
01.
- 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" (display group 010)
Repair Group 01.
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Read measuring value block 10 1 2 0.4V 0.4V
Indicated on display
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).
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24-44
CAUTION!
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 page 24
-45
.
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 Repair Group 01, "Read
Measuring Value Block" function 08, display
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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.
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