Greybeast

How do I access the outside air temperature sensor on my '08 4.2L ? Does the bumper require removal or can it be unplugged going in thru the grille? See part # 40
Clicky: BUMPER & COMPONENTS - FRONT for 2008 Audi A8 Quattro
Thanks in advance.
Mike

haggisuk

MP4.2+6.0

I don't have a pic focused on this exactly, but likely problem w/ other pic/illustration is that is not a fish mouth.

Outside temp sensor is right behind the grill and in front of the A/C panel for starters. Look for it with a flashlight by peering through grill slats. On my W12 (big fish mouth) it is right behind one of the rings of the grill oooo four rings emblem. I never figured out how to remove the upper plastic trim you see preventing access to that area from under the hood, so I basically pried it upward. I stuck a couple of wood blocks in there to hold the resulting crack open since otherwise it really does a number on your hand/skin. Then I (just barely) reached in there and got old one out and new one in. I did not remove the bumper. It has been many years, but I sort of remember that to get it back into the hole in the bracket into which the sensor fits, first I plugged it back in so it wouldn't fall if I lost hold of it, which could be a nightmare in that space. Next I aligned it to the bracket hole from above, using wire connector to guide and maintain position. Then when I had it in the right place, I pushed down on back of connector with a long decent sized screwdriver blade and got it to clip into the hole. I could not do it with just hand pressure. I think to get it out to start I went in from the grill with a screwdriver and pried or pushed at the tabs on the sensor that hold it into that hole while pulling up on it with light pressure from above.

Here is a link to when I replaced a W12 horn that is in same area. You can actually see the temp sensor in the pic. Toward the right in second picture. Notice the grill slats with the rings and light coming through them for orientation. Different motor, but gives you a general sense. https://www.audiworld.com/forums/a8-...ssles-2886010/

BTW, having done this and posted on it as part of trying to get my AC to work better, in retrospect it was the refrigerant refresh that did it. If you are after an AC issue that is? This was maybe 3 or 4 years ago now, so my 2006 would have been younger than your 2008 now. By weight mine was almost half down. New charge and it worked great. I had previously replaced both inside and outside sensor, but longer run it did not fix the problem. My outside temp reading was always correct. If your displayed temp reading is whack then obviously change it.

Greybeast

Thanks for the rapid reply with that link. My OAT display is incredibly sluggish when starting the car then will drop\rise very slowly to the 'correct' temps. Remember the issues I have with the 'hot\no start'? Well, my (ex)Indy shop basically through their hands up leaving me to my own devise. Nice guys, huh?
I'm kinda grasping at straws right now and have a feeling that OAT sensor ties into hot\cold start parameters. Hmmm...am I onto something??

MP4.2+6.0

I don't know if that sensor is used for fuel system at all. Back when they first came in on 5000's it was just used to drive the old HVAC control they bought from GM out of a Cadillac. Vague memory is that fuel system gets intake air temp. from the MAF.

Don't remember your history on hot no start issue, but most common part that seems to come up for that is the basic crank sensor.

the_duke

My OAT is sluggish as well. I think that's intentional due to it's proximity to the radiator. They want air moving across the sensor before it gives you a temp or it will be skewed by the radiator. But as MP said above it isn't used by the ecu for fuel calculation. Somewhere (maybe part of the MAF) there is an IAT (inlet air temperature) sensor. That is what the ECU uses.

Greybeast

Thank you. That makes a lotta sense. If anyone knows where that IAT sensor is located, game on. My issue has always been OAT related. Once above 55-60 degrees the issue rears it's ugly mug. Now that the temps have been Florida-like, the problem is more current and annoying. Feathering the skinny pedal always seems to bring the engine to life after an extended crank.

the_duke

Sounds like a coolant temperature sensor(CTS) issue. The ecu thinks the coolant is colder than it really is. Therefore it adds more fuel. Not an issue when it's cold outside, but when temps rise it over fuels and makes starting difficult. Feathering the pedal allows more air in and helps get it started.

Keep in mind this is a complete guess. This is a common problem on the C5 2.7t but i'm not sure about the 4.2 fsi. It could be any number of other things.

Greybeast

Both crankshaft position sensor and coolant temp sensor have been replaced....at no avail. They were relatively inexpensive and been the culprit on several owners threads here so I gave it a shot.

MP4.2+6.0

Vacuum leaks?--hoses, injector seals, etc.? Bad suck pump (aka suction air pump; Y or T shaped plastic thing in bigger vacuum line tied to power brake unit vacuum)? Also, try taking oil cap off at idle to see if it is pulling a lot of vacuum inside engine (bad PCV). Just various ideas around things that can drive a lean mixture and then harder start.

As a basic diagnostic if you haven't already, pull MAF sensor connector off and see if car keeps running pretty smoothly or really has a hard time. Should run decently if things in order. Poor running means MAF is telling ECU to make a lot of mixture changes from the norm. Indirectly that tells you there is a fuel or air issue--or MAF itself.