Outside temp sensor replacement?

[Glen]

Has anyone replaced the outside temp sensor? The one mounted in the front bumper. Recently, the LCD panel was reading high (110F in 50F temps) so I replaced the LCD with a used one. Now it's reading 132F, LOL. I tested both the original and replacement panels in another W124 and confirmed the original is bad, reading low by 11F. The replacement is displaying correctly so it must either be the bumper sensor or wiring. My main question, is where does the external sensor terminate? Fuse box or behind the dash?

Thanks!

 

[gsxr]

Glen, it terminates in the fuse box. The wire routes along the fender by the EZL after passing by the coils, aux fan resistor, etc.

There's a spec in FSM for various temps / resistances if you want to check the sensor with a meter before replacing. I've found the LCD's are rarely more than ±1° off when bench tested.

 

[Glen]

I just measured and got fluctuations between 950 and 1100 ohms at ~62F. I think this corresponds to the 132F to 136F I see on the display. Prognosis: bad sensor.

Thanks Dave!

 

[Kridre]

You can replace the thermistor at the front for less than $1 and save yourself a hassle of rerouting the wires. You need 3.3KOhm NTC thermistor, buy 5 of them. Test them one by one it should be as close as possible to 3.3KOhm in 20 degrees Celsius (68 degrees Fahrenheit).
It is just the mater of cutting the wire as close to the metal housing as possible, drilling old hot glue, soldering new thermistor and hot gluing it back in to the metal housing.

Did 3 times already, all of them work perfectly.

 

[Glen]

@Kridre, do you have a link to the thermister you used?

 

[Kridre]

@Kridre, do you have a link to the thermister you used?

I bought it at my local shop so sadly I don't have any. Here is a picutre how it looks like, transmission drain plug for scale. You should find it at any shop that sell resistors and other misalenius electrical components.



Edit: I found something online here.

 

[DerFuror]

I addressed a similar situation this way

 

[Glen]

Just want to close off this thread. I picked up a used sensor from a local salvage yard and spliced in a water proof connector. Temp is now reading correctly.

 

[LWB250]

Glad a used one worked out for you, Glen.

I believe that I wrote up a "How To" for replacing a failed sensor with the thermistor for future reference for others who might see this thread. I just saw one of them in my desk drawer the other day...

HOW-TO: Repair Outside Air Temp Sensor in Front Bumper | "HOW-TO" Tutorial Articles

Dan

 

[luckymike]

That's a great writeup, Dan. And coincidentally, it looks like it's finally time to put the thermocouple you sent me into service.

 

[Jlaa]

Just want to close off this thread. I picked up a used sensor from a local salvage yard and spliced in a water proof connector. Temp is now reading correctly.

good use of those waterproof connectors that seemingly always come in packs of 50!