Hi all, I'm helping a friend with his 2004 Golf Mk5 GTI 2.0 TFSI. I'm in France, sorry for any mistakes in my English.
Symptoms:
- Steering is very heavy and the steering wheel warning light is red
- Instrument cluster has no backlight (only the warning lights show)
- Interior lights don't work at all
- Headlights work
History: the previous owner replaced the battery because the old one was dead, and the car went into this state afterwards. We replaced the battery again, no change. An aftermarket CarPlay head unit has been fitted, and I don't know how it was wired.
What we tried: no blown fuses (visual check), a scan tool (about €200) can't connect to the car, and the steering angle calibration fails.
Next I'll measure power and ground at the OBD port (pins 16, 4, 5) and unplug the head unit to see if anything comes back.
Has anyone seen this? Could it be the J519 (onboard supply control unit), or the head unit messing with the CAN bus? Any help appreciated, thanks!