2 questions: temp gauge and transmission
 

Hi everyone. My first post, Yah! I recently bought a 2001 A8 in very clean condition (AUX, FBF). The previous owner kept meticulous care of the car along with detailed maintenance records and receipts. Prior to my purchase, he mentioned a problem with an engine coolant sensor and suggested that it may need to be replaced. After I bought the car I ran a VCDS scan and, sure enough, noticed this:

Address 01: Engine Labels: None
Part No: 4D0 907 560 AF
Component: 4.2l V8/5V G 0002
Coding: 07753
Shop #: WSC 00000
VCID: 6A8DC0AC756060E7201-513D
WAUML54D41N000XXX AUZ7Z0Y1368106
1 Fault Found:
16502 - Engine Coolant Temp. Sensor (G62)
P0118 - 35-10 - Signal too High - Intermittent
Readiness: 0000 0000

I don’t presently have a CEL warning. The car seems to run fine. Funny thing, though, is that a couple days ago the cluster temperature gauge began responding slowly even though the engine was warm. About 10 minutes later, after the engine was definitely warmed up, the temp gauge needle fell back to “zero” and stayed there awhile before resuming its previous position. Question: is that a symptom of a faulty engine coolant temp sensor, or does it suggest a wiring—or gauge—problem?

My second question has to do with the issue of preventative transmission work. So far as I can tell my transmission operates fine. The car has 112,000 miles and, like I mentioned, has been well cared for, with all the regular maintenance done including trans oil changes, etc. Basically, I have the same question as the OP in this thread (https://www.audiworld.com/forums/a8-...dvice-2963025/), which is: Should I mess with the valve body by either installing a new Transgo valve or sending the valve body in to Eriksson, or should I leave well enough alone. ‘If it ain’t broke, don’t fix it’ comes to mind. OTOH, if I have a chance to prevent a blown transmission, then I’d definitely like to do just that.

Replace the temp sender, this is no big deal but I recommend tying a thread to the plastic retaining clip as I dropped mine into the engine a few times when I did one.

Re: the trans work see the earlier related thread. I recommend the TransGo valve and if your lower VB is badly worn I say just replace it for $150 rather than pay to have it reamed oversize and then have to put in the oversize valve. That probably costs more and IMO the TransGo valve with it's fiber scarf-cut seals will reduce or eliminate the steel-on-aluminum wear in that valve, at least on the important end. I have a thread on this swap and there are pics from a Jaaaag forum.
I guess if I bought a D2 tomorrow with 100K on it that'd be my plan unless I knew it'd already been done. New lower VB, TransGo valve, filter (short round pickup), gasket (OEM style), Valvoline MaxLife synthetic ATF and yet another ATF scalp treatment.

Thanks Jfrahm.

Sounds like a new temp sensor is in my future this week. I'll watch for the clip :)

I looked through the receipts that came with the car and, although the trans oil has been changed at least three times since new, I don't see any evidence that the valve body has been examined. I'll call Eriksson tomorrow to sort out details. The car drives so brilliantly that I'd like to keep it in nice condition for as long as possible while also avoiding a potential $$$ transmission problem later on.

A quick update: I replaced the coolant sensor and cleared the code. Problem solved. BTW, that was a great tip about tying string to the plastic clip. I fumbled the clip a couple times and the string saved it from dropping out of sight.
As for the transmission, I called Eriksson and ordered a new valve body. Should be here soon. Thanks again for the recommendations.