BigPorscheGuy

Hey folks, I have a 2004 Porsche Cayenne S with 109k miles. I encountered some radio head unit issues today. On startup this morning, my radio did not power on with the car. I had to power it on manually by pushing in the volume button. After driving a bit, I noticed: the outside temperature would not show on the radio (but showed on the instrument cluster just fine), all steering wheel controls for the radio were not working, the instrument cluster screen would not show the radio station, and most importantly the radio refuses to turn on and off with the car's ignition (as it should). As I remove the key from the car, step out, and lock the doors, the radio stays on and playing music the entire time (even after doors locking). Usually, the radio turns off right after pulling the key out of ignition. This forces me to manually turn the radio off via the volume button each time I turn off the car and walk away. When I start the car again, the radio does not turn on and I have to manually turn it on via the volume button. Other than this, all functions of the radio works properly.

Here's the kicker: along with these issues this morning, as I flipped the headlight switch to fully on, I got a "Check Dipped Beam" light. So I got out and looked at the left headlight to find that the light was out. I replaced the headlight and, on startup, the "Check Dipped Beam" message was gone, the headlight worked, and ALL of the radio issues went away. The radio functioned perfectly showing outside temp, turning on and off with the ignition, steering wheel controls working, and instrument cluster showing the radio station. This made some sense to me as I concluded the left headlight (or both headlights) were on the same electrical loop as some radio functions. I thought all was working.

After an hour of driving, the radio powered off by itself and went back to its exact previous state with all of the previous issues (steering wheel controls non-working, radio refusing to turn off and on with ignition, etc.). This is how the car sits now. Basically, the car is in the exact state it was this morning except the headlight is fully functional with no "check dipped beam" message. I have tried resetting the radio using code 148, removing fuses 8-12 on passenger side fuse box (radio related fuses), disconnecting the car battery, and removing and reconnecting the left headlight. Nothing has worked and the car remains with the radio issues.

Possibly another useful piece of information: I successfully replaced the primary fuel pump and fuel filter yesterday. I did briefly start up the car with the secondary (passenger side) fuel pump connector unplugged mistakenly. I quickly plugged it in and restarted the car and ensured both fuel pumps are in working order - which they are. No idea why this would be linked to radio issues but I'm trying to think of anything.

Main annoyance is I do not want to forget to turn off the radio after turning off the car and come back to a dead battery. If anybody can be of any help here, it would be much appreciated. Thank you!

slavie

I would suspect CAN-BUS issues. On these cars, the radio received constant 12v - there is no switched 12v source. The ignition state, steering buttons, are all communicated via the CAN-BUS.
Headlights, wipers, and radio are all on the same CAN-BUS line. Check your wipers - I bet you're having issues with those as well when the radio is acting out.
You'll need some tools to diagnose CAN-BUS. Maybe the wire rubbed through somewhere, maybe something failed. Hard to tell. This being an intermittent issue will make it even more difficult to diagnose, but such is life sometimes.

theprf

Have you checked the wiring splices under the carpet?

phatz

How big?

BigPorscheGuy

Thanks for your reply. This helped a lot. As you said, the wipers did not work either. I went further into my scanner and found multiple codes, one pointing to the Magnetic Field Sensor (Compass Control Unit). So I looked into this a little further and thought back to replacing the fuel pump. As I lifted the backseat, I found a pinched and cut wire on the compass module under the backseat and above the carpet covering the fuel tanks. As you said, a wire rubbed through somewhere. I am soldering this wire together and it looks like everything will be back to normal

Thanks for your help here!