The brief
It was getting dark and Mr Sung couldn't turn on the headlights on his Q5. Driving at night with no head or tail lights isn't just dangerous, it's a traffic offence, so he brought it straight in. A lighting fault like that needs a scan to find the cause rather than a guess at bulbs. The exterior lights on this car are run by a control module, the J519 onboard supply control unit, which manages the headlights and a lot of the body electrics. When it develops a fault inside, the lights it controls stop responding, even though the bulbs and wiring are fine. A failed module doesn't recover, so it gets replaced, and a new module has to be coded to the car so it integrates properly.
The diagnosis
The computerised scan revealed a faulty headlamp module, the J519, which is why the headlights wouldn't come on. The bulbs, the switch and the wiring were fine, the module was the fault. That's a J519 module replacement with coding to the car, rather than chasing bulbs or wiring that weren't the problem.
The work
The faulty J519 onboard supply control module was removed and a new genuine Audi part fitted, then the coding procedure performed so the new module integrates properly with the car and manages the lighting and body electrics correctly. The fault codes were cleared and every light and function checked. A function check confirmed the headlamps coming on, the tail lights and the rest of the lighting working, all functions normal, and no fault codes.
The outcome
The headlamps coming on, the tail lights and all the lighting working properly, the body electrics normal, no fault codes, and the car safe to drive at night. Mr Sung got the Q5 back able to see the road at night. Scanning it rather than guessing meant we replaced the module that had actually failed, and coding the new J519 in is what brings the lights and the body systems back online, so he can drive safely into the night again.
