2012 Audi Q5 No A/C
Vehicle came in win no AC operation. Vw and Audi has a function in the data stream that shows AC off codes.
This vehicle had an off code of 13.
When scanning for codes, we had codes for no communication for the AC pressure switch, air quality sensor, and vehicle electrical control module.
When I get a bunch of codes, one of the things I do is look for commonality. I decided to pull up a wiring diagram,
Looking at this diagram, it's plain to see that these sensors and module share a LIN bus. Without reading service information we can infer that this sensor works like a module and doesn't produce an analog voltage, rather it is some type of square wave. If we tap into the LIN wire, we should expect to see some type of activity on the line.
This is what I saw when hooking up the scope to the LIN wire.
As you can see, there isn't much going on here.
This is after disconnecting the sensor.
Well there's your problem. These switches have a high failure rate. This coupled with the fact that they look and fit identical to analog type switches compounds the problem. I have seen many new switches be bad out of the box. Always check the part numbers on the switch and make sure to get them from a reputable parts distributor.
A new AC sensor from Audi fixed this issue.
Thank you for reading
Nice Writeup. I did an article about these pressure transducers for MACS in 2017 and it was rerun in service reports this month nxtbook.com/nxtbooks/macs…