Significance of Malfunction Indicator Lamp (MIL)

Significance of Malfunction Indicator Lamp (MIL)

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







- Malfunction Indicator Lamp (MIL)

NOTE: The Malfunction Indicator Lamp (MIL) can blink or remain lit continuously. The DTC memory should be checked in either case.

- Blinking: There is a malfunction that causes damage to the catalytic converter in this driving condition (e.g. combustion misfire). In this case, the vehicle must only be driven at reduced power.
- Continuously lit: There is a malfunction that causes increased emissions. Check the DTC memory for Motronic ECM and automatic transmission (if equipped).
- If there are drivability problems or if there is a customer complaint and the exhaust MIL is not lit, the DTC memory must be checked. There may be DTCs stored that do not cause the exhaust MIL to light up immediately, but only if the malfunction is recognized again after repeated engine starts.

Function test
- Switch on ignition:
- Exhaust MIL must light up

If exhaust MIL does not light up when ignition is switched on:
- Check wire from ECM to exhaust MIL as follows:

Cause: Corrective action:

MIL is not being activated or is - Switch ignition off.
not lighting due to an open - Connect VAGI 598/31 test box
circuit.
- Bridge sockets 2 and 47 of test box.
- Switch on ignition.

Exhaust MIL must light up.

If exhaust MIL lights up:
Replace Engine Control Module (ECM)

If Malfunction Indicator Lamp (MIL) does not light up:
- Switch ignition off.
- Locate short circuit or open circuit from ECM to exhaust warning lamp (instrument cluster) using wiring diagram and repair.

If no malfunctions are found in wire to exhaust MIL:
Malfunction cause Instrument cluster faulty, replace instrument cluster

If exhaust MIL does not light up when ignition is switched on, continue test as follows:
- Start engine and let run at idle:
- Exhaust MIL must go out after a few seconds
- If Malfunction Indicator Lamp (MIL) does not go out:
- Check DTC memory. DTC Memory, Checking

- If there no DTCs are stored:

Cause Corrective action:
Malfunction Indicator Lamp (MIL) is Switch ignition off.
constantly activated due to a short
circuit to Ground (GND). Connect VAG1598/31 test box

Measure wire resistance between socket 47 of test box vehicle Ground (GND).

Specified value: infinite Ohm

If specified value is not obtained:
Short circuit to Ground (GND) in activation wire from ECM to exhaust MIL.

Locate malfunction using wiring diagram and repair.

If specified value of infinite Ohm is obtained, and no short circuit to Ground (GND) is located:

Malfunction cause Engine Control Module (ECM) faulty, Replace ECM.