Repair manual

SULEV 2.0L TFSI Engine
37
Automatic Starter Control in the
Audi A3
To ensure that the Audi A3 easily achieves SULEV exhaust
emission limits, an automatic starter control system is
used.
The ECM does not allow fuel to be injected into the
combustion chamber until a pressure of at least 870
psi (60 bar) is measured in the fuel rail at start-up. This
pressure is necessary to keep raw hydrocarbon emissions
to an absolute minimum.
The complete starting cycle is performed automatically
after briefly turning the ignition key to the start position.
Requirements for Starting
On vehicles with manual transmissions, the starter motor
will only engage when the clutch pedal is fully depressed.
On vehicles with automatic transmission, the selector
lever must be in position “P” or “N,” in addition to a short
press on the brake pedal.
Starting Sequence
(refer to diagram on next page)
To activate the starter motor, both signal lines (1) and (2)
are pulled to ground by the ECM. One of the two lines
is pulled to ground for approximately three seconds for
diagnostic purposes. The other line is always diagnosed
when the engine is started.
After completion of the power-off diagnostics, both lines
are diagnosed continuously by means of pulses with a
short duration of only a few milliseconds. This results in a
mean voltage level of approximately 3 to 9 volts.
When line (1) is pulled to ground, battery voltage will
again be present at the line (3), causing Power Supply
Relay Terminal 50, J682 to close. Likewise for diagnostic
purposes, the actual circuit status of the J682 load output
is fed back across the diagnostic line (4) to the ECM and
Vehicle Electrical System Control Module J519.
Because the starter motor has high inductance, it takes
up to approximately three seconds after the opening
of Power Supply Relay J682 until the ground signal is
restored on the diagnostic line (4).
Effects of Failure
If a fault relevant to starting is entered in memory, only
one manual start will be performed as a substitute
response. The starter will only be activated as long as the
ignition key is turned to the start position and held there.