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Old 12-04-2010, 08:15 PM
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Location: TX
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digital temp display

Hi guys,

Ive been trying to sort out the digital temp display on the 95 E300D - I traced the wiring back to under the fuse box and disconnected the connector, it still showed 136 degrees F. (I read that it should show the minimum when disconnected)

When testing the sensor itself, it shows a resistance of 3.31K ohms in 72 degrees weather. Tested the sensor wiring for a ground input and it sure has negative continuity at the brown wire.

What else did I miss - or is my display shot - Whenever I start the car - it shows 136 degrees and goes out after a minute or so, sometimes it never shows up at all.
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Old 12-04-2010, 09:25 PM
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could just be the screen controller. they do go bad
1987 300TD 311,000M Stolen. Presumed destroyed
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Old 12-04-2010, 09:54 PM
is thinning the herd
Join Date: Mar 2010
Location: Columbus, Ohio
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Having the same exact problem with my 92. Read higher and higher every day, now its just stuck at 136* and sometimes the screen is lit up but blank.

No help, but you're not alone.
Current: 68 280SL, 70 300SEL 3.5, 72 350SL, 72 220, 87 300D, 87 200TD Euro, 90 190E 2.0 Euro, 06 E320 CDI, 72 220D, 72 280SEL 4.5

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Old 12-04-2010, 10:01 PM
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Mines convinced it's either 1 degree out or +135
1987 300TD 311,000M Stolen. Presumed destroyed
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Old 12-04-2010, 10:23 PM
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Join Date: Mar 2006
Location: Sonoma Wine Country
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The sensors rarely go bad -- they are simply a resistor "bred" to be especially heat sensitive. At the display, if the sensor wire is open, the display should show a maximum low temperature (-36F or so). If the sensor wire is shorted to ground, it will show maximum high temperature (+130-something F). The display is programmed to go blank if the reading sticks at either high or low for more than a few minutes.

The usual culprit is the LCD display -- it turns black (all or part). The electronics that translates the sensor resistance into a digital signal for the LCD can also fail. The LCD can be swapped out if you have another and can carefully disassemble the display.

The display electronics is pretty much non-fixable, especially the later versions with a high degree of integration. For all of them there are no internal schematic diagrams available, at least none I've ever seen.

"Buster" in the '95

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1995 E300D (W124) . .239,000 miles My car
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Old 12-04-2010, 11:00 PM
Join Date: Nov 2001
Location: Cape Cod Massachusetts
Posts: 1,427
If anyone figures out their display module is "kaput", I have good tested used replacements available.
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