Ambient Temp Sensor (external thermometer) HELP! - PeachParts Mercedes-Benz Forum

AtlBenz · #1 12-23-2003, 06:24 PM

okay guys, here are a few questions:

1) The outside thermometer (also called ambient temp sensor per FastLane) ...you know... the one behind the front license plate...I think it may be reading wrong. As I have searched the archives and read something about testing the resistance of it. That’s all well and good, but where the heck does the other end connect? The picture on FastLane shows the cable to be like 20 feet long.. I believe too because I have just spent the last 40 min trying to trace it and got no where.

2) Once I find the other end, what should the resistance read at what temp? Obviously as the temp changes so does the resistance. Basically how will know the thermometer is bad?

3) If I deem it necessary to replace it...what’s the best way to do it? Trace it all the way and pull it out only to rethread the new one? OR do I just chop it off a few inches back from the sensor itself, replace it, and reconnect the newone with something I make myself (spade, Molex, or something similar)?

4) If I resort to chopping the tip off, does it make sense to buy the whole thing for approx $50 (as quoted from FastLane) if I am only going to use the new tip and then have 20 feet of cable sitting in my garage?

5) ANY other solutions? Maybe an aftermarket sensor that’s also compatible?

Phhhhhhew. I guess that’s it. The car BTW is a ’94 E420….white of course.

90mbenz · #2 12-23-2003, 07:12 PM

You don't mention your model, but I replaced mine on a 90 300 SEL. Pretty simple. You don't want to cut and splice, and because it's so easy, why bother?

The hardest part was routing through the electrical fuse box area in the cowel area. As I recall, I pulled the cluster and the connector end of the sensor is a direct connection onto the readout in the cluster.

Hope that helps.

Paulwho · #3 12-23-2003, 08:56 PM

The replacement cable is about 15 feet long. The connector is usually located in the fuse box beneath the fuse assembly. Disconnect the battery, loosen the six screws of the fuse cover assembly, loosen the one screw of the fuse tray raise the fuses and look for the two pin connector in the glob of wires. The old sensor is cut at both end and the new harness run adjacent to the oem harness. Disassemble the connector of the new harness at the fuse box to facilitate installation thru the rubber grommet

G-Benz · #4 12-24-2003, 12:24 PM

Paulwho:

Thanks for the tip!

I got mine several months ago from FastLane and have yet to install it as I traced the old one right up to the fuse box on my 93 W124...and never got the gumption to crack the box open and inspect further...

jsmith · #5 12-24-2003, 03:47 PM

G-Benz,

Our 93's are still in sync! I found a couple of fuses that were giving me all sorts of problems and when I replaced them a lot of electrical gremlins cleared up - including the outside temp sensor. It was good for a month then it just died completely. I think it's now the unit behind the cluster which needs to be replaced because I already replaced the thermistor early on. BTW inside the fuse box, you can easily spot the cable because of the brown and green wire...

mhingram · #6 12-24-2003, 05:47 PM

Guys there is a $5 fix buy a new thermistor at an electronics store works great.
do a search there are some good threads out there.
m

jsmith · #7 12-24-2003, 06:15 PM

actually, before you go replacing the thermistor you should check if that's what's wrong with it. you hook up a 3k ohm load across the leads that lead back to the instrument cluster at the connector inside the fusebox and it should read something like 70 degrees...

pulix · #8 05-24-2004, 01:29 PM

I am also having problems with the ambient temperature sensor or temp display:
Last week it started working erratically: It will start at a low or high temperature/fluctuate/blink and fade/completely shut off/and then will revive all of a sudden, as I mentioned before it has been working extremely ERRATIC! Should I replace the outside sensor? and/or should I check for something else? Thanks!

guyever · #9 06-28-2004, 10:10 AM

I was having the same problem on my 98 E320. Couldn't find the sensor where it was supposed to be located, but probed around with my hand back behind the left headlight (from under the hood). I found the sensor and it was just laying there. Still couldn,t find where it was supposed to be so I pushed it through a hole under the light and made sure that it was resting on plastic. My theory is that it was resting on metal and thereby increasing the resistance ie higher temp. Vibrations caused the sensor to lose contact with the metal and then you get a sudden big decrease in temp. Anyway it works great now.
Guy