Hey guys!

New to the forum, hoping someone can help me out with a conundrum I am currently facing.

First off,

I am working on: 2008 Audi B7 A4 Quattro TFSI, 86K Miles


The story...

I got the dashboard alert for coolant a few days back and, of course, I checked the res tank. It was good, so my mind went to the next possible things. At first, I thought it might be a fluke, but the car was definitely overheating, and the next time I started it, it did it again.

So fast forward a bit—I was doing some digging and saw that it could be the Temp Sensor, but because it really was overheating, I went with the possibility of the thermostat.

SO, I replaced the thermostat. Refilled the coolant and ran it for a bit, HOWEVER, I started getting that damn coolant alert again. And this time, the temp needle in my dash was dancing up and down. It would go all the way down and then all the way up and give me the alert.

My mind went to the next possible thing: the damn coolant temp sensor. So I went through the exercise of changing that (and good thing too, the old one looked fried) and I figured that this would make everything hunky-dory.

NOT SO. I ran it a bit and, for a few minutes, everything looked normal. Then the needle started running circles in my dash again. And the alert came again. Damn. HOWEVER, at this point, the engine is no longer overheating, it's just the alert.

So at this point I'm at a bit of a loss, so I ended up going to the Autozone to have them read me the warning codes that might be affecting it, since the 'check engine' light was on as well. They told me that the alert was P0117—which, after doing some digging, I was able to establish means that the circuit for the CTS was low or faulty. But the solve (according to this established ex-mechanic turned Autozone franchise owner) was swapping the CTS—which I had done literally an hour before. I tell him that and he tells me to ignore it for a day or two and it'll stop. That doesn't sound like sage advice to me.

My thoughts/questions are these: At this point I am leaning towards thinking that that wiring for the CTS is messed up, or it may be water pump issues. Has anybody ever dealt with this before? Am I on the right track? Does anybody know how to regrow all the hair I've pulled out in the last few days trying to figure this out?!?!?!


Any and all help/wisdom/advice is appreciated. Rock on, Waynes and Garths.

 

If the water pump was failing as in the impeller was coming apart as they do, you would get an overheat condition.
I suppose if the impeller was coming loose on the shaft it could pump coolant and then freewheel, grab again and pump for a while. It has happened.

A P0117 CTS signal low can be caused by low coolant level, the sensor itself (unlikely in your case), or an open/short in the wiring. Anytime the ECM sees an excessively low voltage signal from the CTS it'll set the code. Doesn't have to be an electrical fault, just the ECM seeing a voltage signal that's implausible (i.e. doesn't make sense with the other inputs).

Try doing the coolant system bleed procedure first, just to be sure ALL the air is out of the system. Anytime an air pocket gets to the CTS, the temp it sees will drop suddenly, along with the gauge and after enough times, set a fault.

Since the CTS is a dual sensor (provied you have the 4 pin sensor) and one part is for the gauge, the other for the ECM for coolant temp input, it's not likely (but is possible) the sensor is faulty or there's a problem with the wiring. Think of it as 2 separate sensors 2 circuits in one package. If the side that sends the signal to the cluster was bad the gauge would jump around but not set an ECM fault code and check engine light.

 

This totally did the trick! I guess it was just a bit of lingering air in the system. All better now.

Thanks so much for the suggestion man!! You rule.