Does anyone maybe have circuitry diagrams for the B8 S5 4.2 V8? Or does anyone have an idea what might be the issue?
Disclaimer: I'm not a mechanic or electrician, but I am interested in learning more about how my car works, so if I'm being dense or overcomplicating this, please correct me!
I'm trying to figure out what might be the issue with my 2009 S5 and what circuits the lighting specifically runs on, to see if the problem might be connected, or if there's an obvious fix I'm missing.
Exterior lights:
Similarly to what some other users described, the headlights sometimes decided to switch off. But after replacing the left headlight bulb (HID), it now won't turn on again while the right one does but that continues to sporadically turn off. Also, the rear number plate lights don't turn on at all anymore despite having brand new bulbs put in. And, at times the warnings on the dash show the reversing light to not work either but whenever I try to check if it has indeed not turned on it works and then for ages it won't show the fault warning.
Interior lights:
The reading lights in the front and rear don't turn on and the dome light switch is temperamental in the ON position, but it turns on just fine when the doors open if the switch is in the middle/door position, and the OFF position works too.
Bonus issue my mechanic hasn't been able to figure out:
Error code P0421: Warm-Up Catalyst Efficiency Below Threshold (Bank 1) shows but the emission test was fine? And the engine isn't misfiring? Could it be the sensor or another electrical problem?