I have a 2004 cayenne turbo and recently been having issues with my automatic lights. When I put the headlight switch to automatic, the headlights always come on, even in daylight. I ran a check on piwis and durametric and get the 1520 error for the rain/light sensor. I have cleared the error and it comes back as soon as the light switch is turned back on. I found a used rain/light sensor which I installed and still have the same problem. I also disconnected the sensor and turned the lights to the automatic setting and they come on without the sensor connected which I am not sure if that would happen anyway. I guess it is possible that the used sensor I got could also be bad. Is there a way to do a resistance check on the sensor. Are there other components in the system I should be checking as well. I did check the fuse and it is fine.

 

As an update, I have been able to narrow down the problem that there is no power going to the sensor from the Wire at the fuse box. The other wire at the fuse block is live but it is not getting to the sensor. Does anyone know where the harness for the rain sensor and mirror travels. Is it down the A pillar on the driver's side?

 

As another update, I ran a new power and ground wire to the sensor and it got the light activation portion of it working again. I will need to check the rain sensor portion but got the codes to finally clear.