I got a whole host of funky CELs almost a year ago now and it turns out they were all due to a faulty engine coolant temp sensor. I replaced it myself (not without busting a breather hose in the process) and no more CELs until a couple days ago. I checked it this morning and the error was Engine Coolant Temperature Sensor: Implausable Signal. Is it reasonable to believe my less than a year old sensor just failed again? Could it be the wire or harness? How long does Audi warranty its parts?

I also had other symptoms like coolant temp that was slow to get up to temp and the coolant temp would also cool down on the highway. It should always stay at "high-noon" once it heats up.

I replaced the ECT first and when that did not fix the problem I replaced the thermostat to find it had cracked and was always open.

I did notice my coolant temp drop a notch or two while on the highway, then climb back up again. Sounds like it could be the thermostat huh?

to get to the thermostat you need to basically put the car in the service position as if you were gonna change your timing belt. I'm not sure if you actually need to remove the tb, but you need to dissassemble the front end as if you were. I've never done a TB change, so I'm not totally sure so someone correct me if I'm wrong.

or take it in to have it done? If yourself, what tips or tricks can you share? How difficult is it, how long does it take, etc? Looks like they require a number of special tools and a fairly involved process.

have installed 2 sets of cams on my car...

You need to put the car in "service position" which involves removing the bumper and pulling the lock carrier (radiator support) forward. You will not have enough room to work unless you do this.

Then remove the timing belt covers. You will see the thermostat housing. It is held in by 2 bolts. You may need to slip the timing belt off the pass side sprocket to get the cover to clear the thermo. Make sure you mark the belt's orientation to the sprockets.

Hope this helps.

it sounds a bit outside my level of mechanical ability (or at least expertise). <prepares to fork over MORE cash>

I love my Audi!(?)