My best advice is to start with the cheapest of the fixes which are the temp sensors. The 2 part numbers are on the first message in this thread. The only problem is that if that doesn't fix it, you will have to go for the thermostat, and the dealership will not return the money to you for the sensor.

You can buy the thermostat in the autoparts warehouse and i even have a coupon if you want it.

Thanks

 

Sorry to revive this old thread. I've had the P2181 code show up and I need some help to track down the cause. I have reset the code and it hasn't come back yet (after a week), but I can tell from looking at the thermal gauge something is not normal.

Is there any way to diagnose the cooling system to narrow down the cause to either a bad sensor, or a thermostat?

It seems if the thermostat was stuck closed the car would boil over, but I haven't had any boiling problems. It could possibly be stuck open, but from my experience, when the T_Stat is stuck open the car may take longer to heat up but the coolant temperature would still rise to normal operating temperature after a while (especially down here in south Florida). However in my case the temperature gauge is just not getting all the up to the normal range (just over the half-mark), it is about 1/8 to 1/4 lower than normal.

I'd like to avoid doing the t-stat if I don't have to, it is a fairly involved task to get at. It would be great if there is some what to test the resistance or something on the sensors to determine if one of the sensors is failing.

Anyone know or have any thoughts how to verify what the cause might be?

 

It's not going to boil over, especially if your in cold temps. Sometimes some coolant will get to the heater core because the tstat isn't totally stuck, but your temp sensor still won't register fully warmed(middle). You still may get heating as well, but usually that code will start appearing more frequently as miles progress.

The fault code and the temp gauge at 1/4 the way is definitely your tstat. Part isn't expensive, just coolant and thermostat. Should be able to do this in a afternoon. Check the DIY thread on this here on audiforums.

 

Thanks Dolamite. I guess I was hoping for something a little more definitive in terms of narrowing down the likely cause. Bear in mind, I'm in south Florida, where the average daily temperature is 80F degrees, and I drive 100 miles daily in traffic, so a stuck thermostat in the closed position would certainly give some indication beyond a low gauge I would think.

If you have a link to that DIY I would greatly appreciate it as I haven't found any for the A4 B7 2.0T Quattro MT6. I'm not sure of the variations, there seems to be DIY instructions for the 1.8T, but I don't know how different they are from my A4.

Is there any way to test the sensors? Perhaps a resistance test?

 

Thermostats don't typically stick closed. Based on it never getting up to temp and the code, I'm 99% sure this is your thermostat. Typical operating temp for this car is around 200F, so even in the 90F summer temps of Florida, you're probably not going to get it up to 200F with the thermostat stuck open all the way and circulating constantly.

The only way to know if it's the sensor without doing the work of changing the thermostat is to change the sensor first (it's easier to get to) and see if the problem goes away. It probably won't, you'll be out the $50 for the sensor, and you'll end up back where you started.

Search is your friend: B7 Thermostat DIY

It's more than I wanted to tackle in my driveway, so I paid a shop (I think) around $300 to do it. Audi wanted nearly twice that.

 

Thanks Wulfgar.

I'm getting a little better at searching the forum, but not sure how to limit searches to B7 models, it seems when I search a get a lot threads from other models.

 

I don't either. I just skim the forum column of the search results to find threads from the B7 forum. That one, I had seen pop up recently, so I sort of knew what I was looking for.

Good luck with it. I really do think it's your t-stat and if you're up for the task, people have said it's not that hard to change. Personally, I have multiple left thumbs and always end up breaking something worse when I try stuff like that, so I left mine up to the professionals.

 

It's not hard at all. The worst part was that lower radiator hose, use the WD 40.

Get the Mahle Bahr t-stat from ecstuning.com. They're Audi's actual supplier, this one is the exact thing, just doesn't have the audi stamp and is much cheaper.

DON'T get the Wahl t-stat, they've been known to leak.

FCPeuro.com is having a G13 coolant on sale for the next two weeks. $19 for a gallon!! That's a thirty dollar value. Don't put anything but G13 or G12 coolant, it'll mess things up.

If you have any questions on the process, feel free to PM me.

 

When my car threw that code, it was a bad thermostat. Up in a Michigan winter, when it sticks open, your engine won't warm all the way up, and the heat, though it keeps the car ok, doesn't have much reserve. The heat was maxed out, and kept the car barely comfortable, but not much more. Force the heater to the HI position didn't make much difference. I also noticed a drop in gas mileage since the engine couldn't warm up all the way.

 

Sorry to bring up an old thread but my 2006 A4 2.0 is throwing the P2181 code and has been for a long time, I have changed the thermostat and cts, is there anything else that could cause the the code? My temperature gauge stays about a quarter of the way up when it is cold and when it is warm it is straight up, sometimes the MIL goes out when it is warm.

Any ideas?

The car runs fine and the heat works good.