Mine was also consistently reading 10C lower before I changed it. One thing I was thinking of doing was to solder a potentiometer in parallel with the two wires coming from the outside temperature sensor. I was then going to adjust the potentiometer until I obtained a correct ambient reading on the display. If yours reads 10C higher you would have needed to connect the potentiometer in series, not in parallel.

I could have used a fixed resistor, but I didn't have the resistance specs of the sensor, Thats why I was going to go with a potentiometer. As you now know, instead of the potentiometer trick, I ended up changing the whole LCD unit. That fixed the problem.

By the way, When I took the old LCD display out, I took it apart to see what caused it to go black at the bottom Left corner. I discovered that the display's miniature light bulb is DIRECTLY behind the black spot that developed, and that subsequently kept on expanding. So its likely that the heat from that miniature light bulb is what finally did the LCD display in.

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'95 E300 Diesel, 264,000 Miles. [Sold it]