Malfunction Indicator lamp (MIL), Functional Check

Malfunction Indicator Lamp (MIL), Significance

Special tools and equipment
- VAG1598/31 test box
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram

Test requirements







- Fuses no. 10 and 29 must be OK.
- Battery voltage must be at least 11.5 volts.

Function test:
- Switch ignition on: exhaust MIL must light.

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

Cause: Corrective action:
MIL is not being activated or is not - Switch ignition off.
lighting due to an open circuit.
- Connect VAG1598/31 test box. Engine Control Module (ECM) is not connected.
- Bridge sockets 2 and 47 of test box.
- Switch ignition on.

Exhaust MIL must light.
If exhaust MIL does not light:
- Switch ignition off.
- Check instrument cluster.

If instrument cluster is OK:
- Locate short circuit or open circuit from ECM to exhaust warning lamp and repair.

If no malfunctions are found in wire to exhaust MIL:

Malfunction cause ECM faulty, replace ECM.

If exhaust MIL does not light 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 exhaust MIL does not go out:
- Check DTC memory, repair any malfunctions and then erase DTC memory, See Erasing and checking DTC memory.

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. Engine Control Module (ECM) is not connected.
- Measure wire resistance between socket 47 of test box vehicle Ground (GND). Specification: 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 found:

Malfunction cause ECM faulty, replace ECM.

- Read readiness code. If DTC memory was erased or Engine Control Module (ECM) was disconnected from continuous B+ supply readiness code must be re-generated.