Ambient temperature sensor

[Nick Jones]

One of the (many) issues I'm trying to sort is the ambient temperature sensor system. Though it seems trivial it seems to affect the way the climate control functions (ie no A/C). Anyway, it irks me to see it display 4ºC when it is >20ºC outside.....

Initially I inspected the G17 sensor behind the bumper and discovered the wires were damaged. I got another (C4 A6 one is the same). Plugged it in with a dash of contact cleaner and it worked....... for about 6 hours...... before returning to it's former ways.

I happened across a thread (http://www.audiworld.com/forums/a8-s...2806177/),that points out that it is also linked to a second sensor in the HVAC intake (G89?). I found this and tested it along with the G17 and found that both had the same resistance (approx 930 ohms @ 22ºC) with the resistance reducing if they are warmed. I think these are ok. Wiring plugs/contacts seem clean, no obvious damage and wiggling the wiring has no effect.

VAGCOM seems to show a sane reading from G89, but a low reading from G17 (though not as low as the dash display). I'm baffled now. Possibly there electronics in the dash insert are sick......

Any info on how these are wired would be much appreciated as having mended the A/C I'd really like to be able to use it!

Thanks

Nick

[johnny_quattro]

ELSAWIN says:

The intake housing of the temperature sensor must not be obstructed.
In case of incorrect measurements, check the blower V42 and associated intake housing.

It makes reference to a dash panel temperature sensor G56 which looks to be below the stereo and above the air con control, although from the diagram I saw looks like a PF dash and not a FL dash.

The only other reference using the search string of 'temperature sensor' relates to the G89 fresh air intake duct temperature sensor. Hope this is of some use. If you need me to take a screenshot, let me know.

[Nick Jones]

Thanks. I have a copy of Elsawin, but have not found the page you reference. Have now found the wiring diagrams in Elsawin - which so far throws up more questions than it answers as G17 seems to be connected to E87 (Climate controller) rather than the dash..........

More wires to wiggle/test!!

Nick

[Nick Jones]

It's resisting repair.

I've temporarily solved it by disconnecting G89 (HVAC intake temp sensor) and shorting it out. This results in a sane reading on the dash (I have no idea why!) and the climate control now functions as expected.

While testing (more rummaging through plugs with MANY pins) I seemed to prove that both G89 and G17 are "earthed" to common returns within the AC loom, but not the same common return and neither of them seems to be connected to true earth. I was able to find a suitable test point for G17 (shares the same return with G56 dash panel temp sensor which is easily accessible) and prove that the wiring for this seems to be intact. I could not find any access to the return for G89. If anyone can explain how these "earths" that are not connected to the body earth function I'd be grateful! I would have though that all temp sensors ought to be connected to the same earth point.....

Nick