Causes for overheat indicator? Preferred 02?

Phil and Judy Rose pjrose at
Tue Apr 15 13:35:12 EDT 2003

At 9:05 AM -0700 4/15/03, Bernie Benz wrote:
>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.  ??

Yes, the 4-pin was the original version. From what I've seen, the
3-pin is not sold under the VDO brandname (IIRC it's "Behlen"
brand--perhaps made under license from VDO). The 3-pin version was
made available as a lower-cost alternative to the original VDO--I
don't know about the "more reliable" part.

I don't think either version is as long-lived as we'd like.  You've
evidently had good luck with the 3-pin model--and/or many others have
simply had bad luck. A local shop tells me they've had many premature
failures of the 3-pin models--perhaps just a bad batch?. If there
actually exists is a "VDO"-branded 3-pin sensor, it might turn out to
be more reliable than the "Behlen" brand. My most recent 3-pin
failure was within a year (less than 10K miles) of its installation.
The replacement I'm about to install is the 4-pin VDO. We'll see.


*  Phil & Judy Rose           Rochester, NY  *
*        mailto:pjrose at       *

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