Air con faults

[quattromark]

So looking into why my aircon suddenly stopped working - It was around the same time as me discovering a massive amount of water in the passenger footwell......This isn't going to take a genius is it!!

I'd already scanned for faults and got the following>

01592 - Air Quality Sensor (G238)
010 - Open or Short to Plus
Freeze Frame:
Fault Status: 01101010
Fault Priority: 3
Fault Frequency: 1
Reset counter: 231
Mileage: 399109 km
Time Indication: 0
Date: 2005.02.01
Time: 12:31:15


Freeze Frame:
Temperature: 19.0 C


00256 - A/C Pressure/Temperature Sensor (G395)
004 - No Signal/Communication
Freeze Frame:
Fault Status: 01100100
Fault Priority: 3
Fault Frequency: 1
Reset counter: 231
Mileage: 399109 km
Time Indication: 0
Date: 2005.02.01
Time: 12:31:15



For some unknown reason I already had a spare G395 - so stripped down the front of the car and replaced the sensor.

No change - still the same codes.

Checked Pins 1&3 for 12V..all good.
Pin 2 had 12v on it.

Checked to see if I was getting continuity of pin 2 to the climate control unit - very high resistance - traced the cable loom (with the help of diagrams) and found that the 17 pin connector at the bottom of the A pillar had corroded - cleaned this up and now have 1.0 Ohm.

However, AC still not working -

For some reason the control unit is not giving out 12v to the compressor valve (N280) and so not activating it.
If I use VCDS output tests I can activate this valve, so its NOT the wiring at fault here - there is a condition not being met that the climate control unit is expecting.

Moving onto the air quality sensor (G238) - where is this located? - because looking at the diagrams, this is supposed to give a signal to the climate control unit on pin C13......however, this space in the connector is NOT populated!!!

One other point, In MVB on VCDS, it states that the system pressure is 50.0 BAR - It should be 28 BAR maximum - however, it does say system pressure is 50 BAR even with the pressure sensor disconnected.
Usually at this point I would replace the pressure sensor with the original......except I seem to have lost it!!

So does the system think that there is too much pressure in it ( ie faulty sensor)?

And also, I have never had an issue with the AC before this point.

Would be interested to hear views on the possible 'phantom' air quality sensor (G238)

[quattromark]

OK - looked into this a bit further......

My car does NOT have air quality sensor - so don't know why it suddenly thinks it does and its faulty..
And with a new pressure sensor not working, I'm beginning to think that the climate control unit has been damaged (indirectly) by the water leak.

[Crasher]

Remind me of the VIN?

[quattromark]

remind me of the vin?


wauzzz4f16n030942

[Crasher]

Yes it does have an air quality sensor, part number 4B0 908 659 A

[quattromark]

Yes it does have an air quality sensor, part number 4B0 908 659 A

OH!!!!

where is this? - I thought it was supposed to fit into a mounting on the air blower casing ( almost a bayonet fit) on RHS of plenum chamber....

The mounting is obviously there (part of casing) but no sensor and no wiring!

Unless I've got that wrong of course!

Also - is that number correct? - maybe 4B0 907 659 A ?

[Crasher]

I haven't got a picture of one and can't t remember doing this exact one, I usually ignore it. The parts system shows the G238 in the intake box and the workshop system just as below in the plenum chamber. Yes, 4B0 907 659 A and £149.40

39774

Hella 6PX 012 684-001

https://digital-assets.tecalliance.services/images/3200/be1c24a31884639498c080c97edb782bd116fd78.jpg?ver=3 .121.0.2c9b2cc592

[quattromark]

I remember having this on my Allroad -it was fastened to the blower casing as per the picture above.

looking at the wiring diagram, it shows the output of this sensor connecting to the climate control unit (J255) via pin C13...... looking at my climate control unit, pin C13 is unpopulated.
TBH it doesn't really matter, I'm not bothered about the air quality bit -

Again, looking at the wiring diagram, the output (LIN) of the AC pressure/temp sensor G935 connects to the climate control unit (J255) via pin C1, BUT it also parallels to the fresh air blower control unit (J126) - Is it possible that J126 is affecting the LIN signal from the AC sensor.

I do have a spare climate control unit, but it comes with component protection!:banghead:

[Crasher]

2006 with component protection?

[quattromark]

2006 with component protection?

Indeed.

when I first got the car the drivers side display did not work - so I got another unit and it flagged as CP activated -

When I did the retrofits, I had to change some modules, CAN gateway, MMI control and central convenience, all had CP.

Found a very good chap in North London (sort of had to pass him on my way to work from Leeds!) sorted it all in an hour.

[quattromark]

I'm out of ideas with this -

The output of the climate control unit (C1) is connected to the blower unit for speed control and also to the AC temp/pressure sensor - The connection is a LIN signal.
The speed control of the blower works fine - the AC pressure temp sensor shows no signal/communication in VCDS.
The line from the pressure sensor to the climate control has continuity as does the connection to the blower motor - This connection parallels in a connector in the ECU box.

The AC pressure sensor shows 51 BAR in VCDS.....it shows the same if I disconnect the sensor!! -
I'm thinking that the new (from Audi) sensor is faulty...

[Crasher]

51 Bar, I didn’t know it could read that high, I don’t see it being the sensor.

[quattromark]

51 Bar, I didn’t know it could read that high, I don’t see it being the sensor.

Well this is my point.... there is no way ANY sensor on ANY car would have / need to measure 51 BAR - thats about 740 psi ...... maybe auto gearbox???

anyway.. my point... if the sensor is short/open circuit.... what does it show - is it 0 or 51 BAR- I am REALLY hoping that the sensor is faulty......irrelevant of whether that sensor is connected or not - vcds shows 51 BAR - so is the sensor open circuit?
It would be really good if someone with an A6C64F could pull the connector on the AC..... however considering the front end has to come off and then AC measured with VCDS, I'm not holding out for many takers!!!!

So, as a proving point - I have ordered ANOTHER sensor from Amazon - will be with me Sunday......lets see what happens.........

[Crasher]

Well this is my point.... there is no way ANY sensor on ANY car would have / need to measure 51 BAR - thats about 740 psi ...... maybe auto gearbox???

VAG common rail Diesel engines routinely operate at 2000 bar (circa 29000 psi) and some are in the 2800 bar range.

[quattromark]

Well this is my point.... there is no way ANY sensor on ANY car would have / need to measure 51 BAR - thats about 740 psi ...... maybe auto gearbox???

anyway.. my point... if the sensor is short/open circuit.... what does it show - is it 0 or 51 BAR- I am REALLY hoping that the sensor is faulty......irrelevant of whether that sensor is connected or not - vcds shows 51 BAR - so is the sensor open circuit?
It would be really good if someone with an A6C64F could pull the connector on the AC..... however considering the front end has to come off and then AC measured with VCDS, I'm not holding out for many takers!!!!

So, as a proving point - I have ordered ANOTHER sensor from Amazon - will be with me Sunday......lets see what happens.........


Well, new sensor fitted - no change ( not really surprised).

The climate control unit is displaying this fault in VCDS.

01087 - Basic Setting Not Performed
005 - No or Incorrect Basic Setting / Adaptation
Freeze Frame:
Fault Status: 01100101
Fault Priority: 2
Fault Frequency: 1
Reset counter: 231
Mileage: 358911 km
Time Indication: 0
Date: 2023.10.29
Time: 17:10:35

However, it has been showing this for 2 years - but oddly enough it will not let me perform a basic setting on it - fails everytime.

My next step is to get the CP removed from my spare Climate control unit and see where we go from there.

[dan2485]

You may need to do the addressing in the Basic settings as it may not recognise the new sensor, then try again.

[quattromark]

Well, I hate to admit this but I'm out of ideas!

I have spent all day looking for this air quality sensor - I know a lot of people don't bother with them as all it does is activate the re circ flap, however, I'm not sure how this interacts with the AC pressure/temp sensor.
According to the drawings I have, the air quality and pressure sensor are not connected - they have individual inputs to the climate control unit..........HOWEVER, I have been legged up with these drawings before.
It is possible that the air quality sensor is messing up the LIN signal if indeed they are joined......Its a shame I can't find it.

I have removed the blower motor box completely- Air quality sensor (or wiring) no where to be seen - I found the air temp sensor inside, but thats it!
Also removed A LOT of the dash so I could see which of the flap actuators were faulty so I can get them replaced.....Again, found temp sensors but no air quality sensor.

I'll have a look at ERWIN when I get time this week and probs print the wiring diagrams from it - just in case mine aren't correct.

[Crasher]

I find it odd the sensor isn’t there but I can’t see it causing the problem.

[quattromark]

So after subscribing to erWIN it turns out that I do have the correct diagrams after all -

What I did notice however, was that on the parts page for the AC, it shows the Basic AC climate control unit for my car, not the all singing flashing controller that I have fitted - I think its called the 'convenience' package - which incidentally the Air quality sensor is marked as being part of - Now I'm thinking that I don't have a sensor because I have the basic package/controller which the sensor is not part of. Could the controller have been retrofitted by previous owner?
Anyways, It does not matter - just want my aircon fixed - going to see if my tame Audi parts dept will exchange the genuine pressure sensor I bought for another unit just in case it is faulty.

[quattromark]

Well, that's a lesson learnt!!!

Turns out that the new pressure sensor from Audi WAS faulty after all!

Got a replacement from Audi, installed it - AC kicked in straight away!!

As for my 'missing' air quality sensor.......It's not missing - there isn't one. I got the tame Audi parts chap to do a bit of digging - my car came out of the factory with the 'basic' climate control unit, which does not utilise the air quality sensor - at some point, someone has swapped the basic controller for the convenience controller.

This means that the 'sudden appearance' of the G268 fault was a figment of my imagination - it had always been there!!:banghead: