In a nutshell.......

Air Con stopped working - did VCDS scan, came up with 2 culprits.

00256 - A/C Pressure/Temperature Sensor (G395) 
            004 - No Signal/Communication
             Freeze Frame:
                    Fault Status: 01100100
                    Fault Priority: 3
                    Fault Frequency: 1
                    Reset counter: 232
                    Mileage: 399109 km
                    Time Indication: 0
                    Date: 2025.09.23
                    Time: 13:54:56
 

01592 - Air Quality Sensor (G238) 
            010 - Open or Short to Plus
             Freeze Frame:
                    Fault Status: 01101010
                    Fault Priority: 3
                    Fault Frequency: 1
                    Reset counter: 232
                    Mileage: 399109 km
                    Time Indication: 0
                    Date: 2025.09.23
                    Time: 13:54:56

             Freeze Frame:
                    Temperature: 21.0 C

Changed G395 with a new genuine sensor - no change....... not only that, in measuring blocks in VCDS it was saying the pressure was 51 Bar!! - however, it also said the pressure was 51 Bar WITHOUT the sensor connected!!

Did the usual due diligence and traced the LIN wire all the way from the sensor to the climate control unit - full continuity in this cable. I even ran another cable direct from the sensor to the climate control unit - still showing the same issue.

There seems to be some debate around if I have G238 air quality sensor - because IF I have, I can't find it!! - It is NOT where it should be, on a bracket on the air blower box ( I remember my Allroad having this) - and to add insult to injury, the wire that should be from the air quality sensor to the climate control is not present in the connector of the climate control unit - it is un populated - so either the electrical drawing is wrong, or I do not indeed have G238.

I have seen the exact same issue in other forums - but no one has supplied and answer!

Any thoughts?

So finally got to the bottom of this!

 

The new genuine pressure sensor (from Audi) was faulty - simple as!

changed it for another oe sensor, hey presto, got my AC back!

 

As for the 'missing' air quality sensor....wasn't missing - it doesn't have one.

My car came out of the factory with 'basic' AC climate control which doesn't utilise an air quality sensor........it seems that pre my ownership of the car, someone changed the climate control unit for the 'convenience' version, which does utilise an air quality sensor!

Glad you got sorted, sorry we couldn't advise you.