1999 AUDI A4 check engine light

01-3

Malfunction Indicator Lamp (MIL),
significance

If the ECM recognizes malfunctions that lead to a
worsening of emissions values, it indicates them
by lighting the exhaust Malfunction Indicator
Lamp (MIL).

Installation location of exhaust Malfunction Indicator Lamp (MIL)
The Engine Control Module (ECM) switches on the exhaust Malfunction
Indicator Lamp (MIL) after ignition is switched on. Shortly after engine is
started, the exhaust MIL will go out. This requires, first of all, that the
Engine Control Module (ECM) does not detect a malfunction that worsens
the emissions values and, secondly, that activation of the lamp by the
Engine Control Module (ECM) is OK.
If malfunctions that worsen emissions are recognized during operation of
the engine, the ECM switches on the exhaust MIL in instrument cluster.
(These malfunctions are listed in the DTC table). An entry is made in DTC
memory at the same time.
The Malfunction Indicator Lamp (MIL) can blink or remain lit continuously.
DTC memory should be checked in either case Page 01
-12
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01-4

Continuously lit:
There is a malfunction that causes increased
emissions. Check DTC memory for Motronic
ECM and automatic transmission (if installed).
Check DTC memory if there is a driveability
problem or a customer complaint, but the
exhaust Malfunction Indicator Lamp (MIL) is not
lit. There may be DTCs stored that do not cause
the exhaust MIL to light up immediately, but only
after engine is started again and malfunction is
recognized again.

Blinking:
There is a malfunction that causes damage to
the catalytic converter in this driving condition
(e.g. combustion misfire). In this case, vehicle
must only be driven at reduced power!

Note:
Catalytic converter must be checked after
malfunction is repaired.
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01-5

Malfunction Indicator Lamp (MIL),
checking


Function test of warning lamp

- Switch ignition on.


Exhaust MIL must light up

- Start engine.

Shortly after engine is started, the
Malfunction Indicator Lamp (MIL) will go out
if there are no malfunctions stored in DTC
memory that relate to the E-gas system

Note:
The switch-on signal for Malfunction Indicator
Lamp (MIL) is transfered from the Engine Control
Module (ECM) to the instrument cluster via CAN-
bus. Check data exchange between Engine
Control Module (ECM) and other CAN capable
control modules Page 24
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