Plug the diagnostic tool into the OBD2 port. On the Golf MK5, the port is located under the dashboard on the driver's side, behind a small flap below the steering column.

without starting the engine. Make sure the battery is in good condition — coding writes that drop out due to low voltage can leave the module in an inconsistent state.

Open the iCarsoft CR Max, select VW and let it identify the vehicle / select Golf MK5.

Open the control unit list and select 09 – Electronic Central Electric (sometimes labelled Central Electrics or Bordnetz).

The tool will read the current software coding and display it as a long hex string (e.g. 098D0F27 00 41 80 00 14 00 00 14 00 00 00 01 97 07 5C FF).

Write down or photograph the original coding string. This is your fallback if anything goes wrong — you can always restore the car to its original state by writing this exact value back.

Locate byte 18 in the long coding and tick bit 4 – Daytime Running Lights Via Fog Lights. In the iCarsoft helper this option is shown as "10, Daytime Running Lights Via Fog Lights" — the "10" is just the option index in the iCarsoft list, the actual location in the coding is byte 18, bit 4.

Confirm the change. The tool will calculate the new coding string and ask The new code: … Are you sure to set the new code? — press Yes.

Wait for the "coding successful" confirmation, then exit the module and switch the ignition off.

Switch the ignition back on (or start the engine) with the headlight switch in the OFF (or AUTO) position. The front fog lights should now come on as DRLs. With dipped beam or full beam selected, the fog lights drop out of DRL mode and behave normally again.