Don't let the length of this page fool you - replacing the temperature
sensor on an E39 is very, very simple and can be handled by someone
with very modest
mechanical aptitude. It took me about 20 minutes to do and that was
because I was taking time to document the process with my camera.
The external temperature sensor on a BMW E39 is placed within a plastic
fender wall cover that extends very close to the road. As a result it's
easy to damage by rolling into a low curb or parking lot tire stop. My
local BMW dealer told me he sells 30-40 of the components to repair
damage to this area every month and that it is extremely common.
The first sign you may have a problem with your external temperature
sensor is if you have a really low reading. This is caused by the
sensor either being damaged, missing or having an open circuit; the
wires leading to the sensor may have torn off in an impact. Most people
(myself included) get readings of -40d F:
The sensor itself is located directly in front of the passenger tire fender well:
When I checked mine out this is what I saw:
The gaping tear in the fender wall is where the sensor would normally
sit. The fender wall itself is a rather small piece of cheap plastic
that not only provides splash protection from the tire but contains the
housing that the sensor sits in. At this point I went out and bought
the following parts to repair this:
External Air Temperature Sensor
* Prices are from my local dealer with a BMWCCA discount, except for the sensor itself which I purchased from Bavarian Autosport.
In addition I purchased some wire connection terminals from the Home Depot.
I believe they ran about $2. Parts in hand I started putting it all
together. All I needed was an 8mm socket wrench, a short phillips
screwdriver and some wire crimpers.
First, you will need to take apart the plug housing. Pull apart the
green and gray portions of the connector, then slide the white
retaining clip out. There is a very small clip at the bottom of the
plug housing that you will need to lift in order to separate the green
and gray parts.
Next you will insert the two contact wires into the green housing. Note
that the contact wires have small retaining clips that must be oriented
towards the slots in the green housing so that they will snap in place:
Slide the white retaining clip back into place, then thread the ends of
the contact wires through the gray housing and reconnect it to the
Now slide the temperature sensor into the plug housing and this portion
of the assembly is ready to go. Note that there are several small
retaining clips that will help you get the plug to go together properly:
Take the black plastic cover and thread the sensor through the bracket that holds it:
There is a slotted area that the sensor fits in, holding it fairly securely into the cover:
Remove the existing cover from your wheel well. This is where you will
need the 8mm socket and the screwdriver. There are four retaining
screws on the inside of the fender well. I found that turning the
wheels of the car fully to the right left me with ample room to
Slide the black cover straight down, taking care to pull the front
portion out from the forward portion of the fender. With the cover
removed you should see the wires that connect up to the sensor. In my
particular case they were blue/red wires that had been pulled apart at
a previous connection point:
I used my wire crimpers and stripped down the end of the existing wire
then added a terminal connector, just in case my wife drives the car
and this happens again. I then added the terminal ends to the two
contact wires from our earlier assembly and pushed them together:
The terminal connectors I used are not well insulated against any
moisture that may make it past that panel, subjecting them to corrosion
that could affect the readings of the sensor. I wound some eletrical
tape tighly around the terminals to ensure they would stay dry:
It is important to tightly secure the wires, especially where the new terminals have been crimped in.
I used some zip ties to secure them to one of the inner support
brackets so that they would not bounce around and cause the connections
to break. From here it's a simple matter of sliding the new plastic
cover piece back into place. Once reinstalled you will have a shiny new
piece of black plastic inside your fender well:
If you have installed everything properly your dash temperature should
start climbing and within a few hours at most should read the proper
Yes, it was pretty cold in Virginia the day I did this repair! I hope
you find this page helpful. If you find something wrong with these
instructions please let me know and I'll update them; my e-mail address
is dralison (at) gmail.com.
Copyright (C) 2005, David Alison. Thanks to Jim Cash for suggestions to improve this process.