balthus

Hi -

Anyone know why the outside temperature would not be displaying correct temperature? Not sure if coincidence but took the car for first car wash today and happened to notice it when I was leaving. Time display was correct but temperature said 74 degrees when it’s closer to 87 degrees. Did not change as I drove to next destination where I am now. My car is parked outside. Will be curious if it changes. Might it be a fuse? This is a 2017 E400 wagon. Thanks.

DFWdude

The outside temp sensor never gives accurate "ambient" temps. Official ambient temps are recorded inside a weather station (in the shade) 6-ft+/- off the ground sheltered from any wind.

The sensor below the bumper in these cars is NOT ideally located... It measures temps in direct sunlight as often as not, and always off the black/dk gray road surface, which radiates heat much warmer than several feet off the ground. The temp readings in both of my MBs read higher than actual (on average) during the summer.

Cold water used to rinse the car in the car wash will hit the sensor and drive the temp lower.

ua549

Temperatures should not have low readings this time of year unless you are in the Southern hemisphere.
List it on your squawks for your next service visit.

balthus

Just got back in my car - it’s been parked outside - and now says 91 degrees which aligns with the temperature. Odd. I will keep an eye on it. Thanks.

rraisley

Might it not be just the water from the car wash? Certainly it's a lot cooler, and (I'm not sure exactly where the sensor is) might stay wet for a while, and if it's wet and you're driving, then it is evaporating off, which also would cool it. I would think that was it, meaning no problem, it just reads differently when wet.

balthus

Although I don't seem to recall that ever happening before but makes sense. Maybe just Mercury In Retrograde!

2thfxr

My temperature reading does not change instantaneously when I pull out of garage whether higher or lower but does change some minutes latter. I think that is just the way they are designed.

ua549

The sensor needs airflow. Mine registers correctly within 1/4 mile or sooner when driving faster than 15 mph.

konigstiger

If reading does not return to normal have dealer check outside temp sensor (front SAM direct input, pin 16).

BenzC400

Seems like normal operation. In my E53, the temperature always reads lower after a car wash and returns to a normal accurate reading in a few miles. When I leave a cool garage on a hot day, it takes several minutes for the outside air temperature to show an accurate reading. My former C400 worked the same way. I get similar behavior from my Ford’s outside air temperature reading.