Light just came on; 1/4 full gas tank, fuel cap tight. I filled it up with gas and light still on. Replaced air filter 15,000 miles ago which was cause of previous episode. Hate to drive 80 miles to dealer. I also own Taureg which is the same car, but local VW dealer says he cannot read Cayenne's computer. Any ideas?

 

A CEL uses a universal communications protocol (OBD-II and others). You can go to Autozone and have them connect a ScanTool to the port and read the codes. This will give you some initial diagnostics.

 

what said above. a $30 reader from autozone, including the code reference book, and let you know at least what you are looking at.

 

They scanned it and found P0431, buildup?

 

This may be a start.... https://rennlist.com/forums/porsche-...and-p0421.html

Cat inefficiency could be the converter, O2 sensors, connectors to the O2 sensors or the ECU. More diagnostics is needed.

 

I called the dealer and they said that their usual procedure is to read it, clear it and see if it comes back. They also mentioned $2600 worst case since the car is over 80,000 miles. One of my employees told me that he has added fuel additive to eliminate his check engine light being on so I added some and then drove 125 miles and lo and behold the light is off. Thank goodness for Sea Foam! Lets see if it lasts.