Headlamp Control Module: Service and Repair

Removing And Installing Control Unit For Gas Discharge Lamp

Preliminary work
1. Switch off light. Remove main headlight.

Removing control unit for gas discharge lamp

WARNING:
Risk of short circuit.
- Before removing fog light, remove ignition key and switch off light switch.

NOTE:
- The control unit is located underneath the Bi-Xenon headlight.
- The control unit also has the task of driving the motors for the headlight beam adjustment (HBA) of the Bi-Xenon headlight.

1. Open the two locking clips -1- and remove cover -2-.







2. Turn the headlight over and set down on a suitable base.
3. Remove all six fastening screws -3- and pivot up the control unit.







WARNING:
Risk of damage to the control unit for the gas discharge lamp.
- It is essential to pull connectors 4 and 5 straight out.

4. First actuate latch of connector -5- and remove the connector. Open clip of connector -4- and pull out the connector.







5. Remove seal -A- from headlight.

Installing control unit for gas discharge lamp

WARNING:
- Risk of short circuit.
- Before removing fog light, remove ignition key and switch off light switch.
- Risk of damage to the control unit for the gas discharge lamp.
- It is essential to push plugs -4- and -5- in straight.

NOTE:
- The control unit is located underneath the Bi-Xenon headlight.
- The control unit also has the task of driving the motors for the headlight beam adjustment (HBA) of the Bi-Xenon headlight.
- Ensure that the seal -A- is properly positioned on the control unit.







1. Insert connector -4- and secure with locking clip. Push in connector -5- until it engages.







2. Position control unit and secure with the six fastening screws, starting in the centre. Tightening torque: 2 ftlb.







3. Position cap -2-, press on and close locking clip -1-.







Coding

Extracting and changing coding

NOTE:
- Communication with the HBA gas discharge lamp control unit can only be established once ignition and dipped beam are switched on.
- Each Bi-Xenon headlight, left and right, has its own HBA (Xenon) gas discharge lamp control unit. These can be read out and coded separately.
- Following replacement of the control unit(s) for the gas discharge lamp, always perform a drive link test on the HBA servomotor to check that the correct headlight is reacting (correct side)
- Before troubleshooting, always read out the fault memory of the other control unit for the gas discharge lamp, left or right, in order to determine whether faults are related.
- The power supply and the shift function come from the vehicle electrical system control unit.
- The fault memory of the vehicle electrical system control unit should be read out first before troubleshooting.
- If it is not possible to communicate with the (HBA) control unit for the gas discharge lamp in the headlight, this may be caused by incorrect coding, e.g. both headlights are coded on one side. Remedy: Remove one headlight and restart connection setup using the Tester. Code control unit correctly.
- In vehicles with level adjustment (air springs), the signal for the vehicle position is received via the level adjustment system control unit. This has four angle sensors for compression.
- In vehicles without level adjustment (steel springs), two angle sensors - front left and rear left - are installed for compression detection.

Under menu item:
- Special functions
- HBA left or right

Coding can be read out indicating which equipment features are activated and which are not.

The following equipment features can be set:
- Control unit, right
- Control unit, left
- Right control unit in conjunction with level adjustment system
- Left control unit in conjunction with level control system

Read out the fault memory again and erase as necessary.

ATTENTION:
Coding: make sure that the headlight system is coded correctly in the vehicle electrical system control unit (always code Xenon headlights as well).
- Incorrect coding in the vehicle electrical system control unit can damage the control unit for the HBA gas discharge lamp.

Calibration

ATTENTION:
Coding: make sure that the headlight system is coded correctly in the vehicle electrical system control unit (always code Bi-Xenon headlights as well).
- Incorrect coding in the vehicle electrical system control unit can damage the control unit for the HBA Bi-Xenon gas discharge lamp.

NOTE:
- Calibration must be performed in the level adjustment control unit in all vehicles with running gear level adjustment
- The level adjustment control unit provides headlight levelling system parameters to the gas discharge lamp control unit.
- Communication with the HBA gas discharge lamp control unit can only be established once ignition and dipped beam are switched on.
- Each Bi-Xenon headlight, left and right, has its own HBA (Xenon) gas discharge lamp control unit. These can be read out and coded separately.
- Following replacement of the control unit(s) for the gas discharge lamp, always perform a drive link test on the HBA servomotor to check that the correct headlight is reacting (correct side)
- Before troubleshooting, always read out the fault memory of the other control unit for the gas discharge lamp, left or right, in order to determine whether faults are related.
- The power supply and the shift function come from the vehicle electrical system control unit.
- The fault memory of the vehicle electrical system control unit should be read out first before troubleshooting.
- If it is not possible to communicate with the (HBA) control unit for the gas discharge lamp in the headlight, this may be caused by incorrect coding, e.g. both headlights are coded on one side. Remedy: Remove one headlight and restart connection setup using the Tester. Code control unit correctly.
- In vehicles with level adjustment (air springs), the signal for the vehicle position is received via the level adjustment system control unit. This has four angle sensors for compression.
- In vehicles without level adjustment (steel springs), two angle sensors - front left and rear left - are installed for compression detection.

Under menu item Calibration, the gas discharge lamp control unit is adapted to the current conditions relating to vehicle position. During calibration the existing vehicle position is stored as the zero position. Following calibration, the headlight setting must be checked and, if necessary, corrected.

Calibration must be performed if changes have been made that can alter the position of the angle sensors for running gear level adjustment:
- Headlights, complete
- Control unit, gas discharge lamp
- Angle sensors, level adjustment (front and rear compression)
- Running gear components
- Accident damage

NOTE:
- Whenever coding has been changed in menu item Change coding, always quit the menu in the Tester and call up the menu again. Switch light off and on again.
- If the coding does not match the vehicle equipment, faults may be displayed that are not really present.

Read out the fault memory again and erase as necessary.

Subsequent work
1. Install main headlight and perform function test