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From digest.v6.n301 Sun Mar 2 07:36:28 1997
From: Don Eilenberger <>
Date: Sat, 01 Mar 1997 21:58:55 -0500
Subject: RE: <OBC> Way Too Cool

>From: "Robert D. Baron" <>
>Date: Sat, 01 Mar 1997 15:17:04 -0600
>Subject: <OBC> Way Too Cool
>Today, with no prior warning of impending doom, the OBC on my '92 735i
>tells us the outside temperature is an unvarying -535F (and -27.5C).
>All other readouts are normal.
>It's not that cold here in Oklahoma.
>Any ideas or suggestions?
>Bob Baron / '92 735i 55k miles

Bob - given that the E34 and your car share this OBC.. I'll pass on my experience..

In my endless quest to mount a remote radar detector (long not particulary successful story), I unplugged the OBC temp sensor from the car to gain access to an area behind it..

When I plugged it in, I found that the OBC was reading -45F.. and very slowly varying upwards a bit. Being in panic mode (what did I break now?).. I unplugged it again and cleaned the two contacts. Plugged it back in, same thing..

Long-story-short - the failure mode if the sensor goes bad is some temperature that OBC normally never will display (people have mentioned that a working one bottoms out at -35F - which is colder than I ever want to be).

My OBC slowly recovered over the course of a day - and in talking to a mechanic friend who'd been bit by the same thing.. he said this is normal (talk about a slow response curve - although it does seem to respond quickly once stabilized).

Your sensor is probably bad. On the E34 - it is located behind the pop-out panel on the lower left front below the bumper (the matching panel on the right - passenger side - is for the tow hook). It is yellow and black in color - has a yellow body and a black nose about 1.5" long - where the tip sticks out through a hole in the panel. (The panel is right next to the fog light).

Suggest looking for yours and see if (1) it got disconnected somehow or (2) it got hit with some road debris and damanged.

Dunno what the $$$ tarrif on one is.. also don't know what the "normal" resistance is (since it is probably a thermistor or thermocouple - there should be some spec's somewhere on it.. mebbe in the ETM manual, I'll take a look later if you want).


Don Eilenberger
Spring Lk Hts, NJ, USA
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