Malfunction Indicator Lamp: Description and Operation

Malfunction Indicator Lamp (MIL), Significance

If malfunctions are recognized by the Engine Control Module (ECM), they will switch on the Malfunction Indicator Lamp (MIL).







Location of MIL lamp


NOTE: The MIL lamp can switch on in the "Blinking" or "Permanently ON" mode. In either case, DTC memory must be checked. See 'Computers and Control Systems, Testing and Inspection, Procedures, Address word 01, Function 02, Memory Checking.' Testing and Inspection

- Blinking: There is a malfunction which can cause damage to the Three-Way catalyst if driven in this condition. In this case, do not drive the vehicle under full load or wide open acceleration!
- Permanently ON: There is a malfunction present which will increase exhaust emission levels. checked the Engine and/ or Transmission Control Modules.
- If the MIL lamp does not light up, even though there is an engine running problem, or if a customer complains, after the MIL lamp has been functionally checked of; DTC memory must be checked, because malfunctions which do not immediately switch the MIL lamp ON can still be stored!

MIL lamp, functional check
- Switch ON ignition
- MIL lamp must light-up

If NO
- Check MIL lamp wiring as follows:

Cause:
Malfunction Indicator Lamp (K83) is not activated or does not light-up for open circuit

Remedy:
- Switch OFF ignition
- Connect VAG 1598/18 Test Box
- Bridge Test Box sockets 1 and 5
- Switch ON ignition
MIL lamp must light-up
If MIL lamp does not light-up
- Switch OFF ignition
- Check MIL lamp LED
If LED is OK
- Locate/eliminate open circuit between ECM and MIL lamp via wiring diagram

If no malfunction can be detected in wiring to MIL lamp:

Malfunction cause
Control Module J220 faulty, replace.
Erase DTC memory and create Readiness code.

If MIL lamp lights-up (ignition switched ON) continue as follows
- Start engine and let idle
- MIL lamp must go out after a few seconds

If MIL lamp does not go out
- Check DTC memory. See 'Computers and Control Systems, Testing and Inspection, Procedures, Address Word 01, Function 02, Memory, Checking.' Testing and Inspection

If no DTC's are stored

Cause:
Malfunction Indicator Lamp (K83) is permanently activated by short to ground

Remedy:
- Switch OFF ignition
- Connect VAG 1598/18 Test Box
- Measure resistance between Test Box socket 5 and ground:
Specification: Infinity Ohms
If specification not obtained
Short to ground in signal wire between ECM J220 and MIL lamp
- Locate and eliminate malfunction using wiring diagram

If the specification Infinity Ohms is obtained and no short to ground can be found:

Malfunction cause
Engine Control Module J220 faulty, replace: See 'Computers and Control Systems, Engine Control Module, Service and Repair.' Service and Repair
Erase DTC memory and create Readiness code:
See 'Computers and Control Systems, Testing and Inspection, Procedures, Address Word 01, Function 02, Memory, Checking.' Testing and Inspection

See 'Computers and Control Systems, Testing and Inspection, Procedures, Diagnosis With Scan Tool, Address Word 01, Readiness Code Creating.' Testing and Inspection