Causes for overheat indicator? Preferred 02?

[Bernie Benz]

Phil,

My experience over the years on 4 Audis, re: 3 pin vs 4 pin MFTS, has been
that the 3 pin "passive" sensor is the more reliable of the two.  Further, I
believe that the 4 pin "active" version was the original factory installed
unit and that the 3 pin version was later made available by VDO to replace
the problematic 4 pin MFTS.  ??

Bernie

> From: Phil and Judy Rose <pjrose at frontiernet.net>
>
> The "low coolant/overheat" warning is a common symptom of MFTS
> failure. If this is your situation, you'll also find that your boost
> is limited to about 1.4 bar and your A/C is inoperative. The coolant
> level sensor will also generate these symptoms if it is defective,
> but that seems to happen much more rarely than MFTS failure. The MFTS
> failure is, as you probably know, very common--especially the 3-pin
> version. The 4-pin (VDO) version is available for the same price and
> is possibly (hopefully!!!) somewhat more robust. Generally, when the
> 4-pin version fails, it affects the temp gauge reading.
>
> Phil