my outside air temp is reading -36, I replaced the sensor but it still reads the same, I disconnected the battery for awhile hoping it would reset, but it did not, AC works fine and its not giving any codes. any ideas? TIA

 

broken wire or loose connection most likely. check for short to ground or short to positive on the two wires that go from the sensor to the fuse along the right side fender.

 

It's a simple circuit driven by the Instrument Cluster's microprocessor. Here is how it works:

The GREEN wire is a constant current source and with no sensor plugged in, it should have 3.00 volts in it, referenced to ground of course.
The BROWN wire always shows about .05 volts, it is close to ground.

Both wires go directly to the connector at the Instrument Cluster, if the display lights up, it is not a fuse.

At 3 volts, the display shows -36F (or C equivalent).
The sensor is a variable resistor and its resistance goes lower as the temperature goes higher, 91F (or it's C equivalent) will lower the resistance of sensor such that the voltage will drop to .96 volt.

To measure the voltage with the sensor plugged into it is impossible as there is no exposed contact on the back side that you can get to. I used a "tap" to measure the voltage both with sensor unplugged and sensor plugged in with the garage at 91F.

NOTE THAT IF THE BROWN wire is open, you will have 3 volts on the green wire and a temp of -36 at all times. So with the sensor plugged in, you should see around 1 volt on the green and ZERO on the brown.

I strongly suspect you have an open in the green wire, probably right inside the connector at the sensor, tho it could be father up towards the IC but the manual claims there are no other connectors in line between the two ends.

 

Thank you, that’s a lot to digest, for me anyway, any idea where I can get a new connector?

 

Can really tell by just looking, look’s intact, I’ll put a meter on it when it cools down

 

I really don't know that the problem IS the connector, but it might be. I am unsure if you can get the sensor or the connector for the Crossfire - but the SLK320's sensor and connector are the SAME ITEM.
You might search for "ambient" or "outside" temperature sensor and connector for the SLK320.

THere is, of course, always the local salvage yard - look for a car that was rear ended!

 

I’ve been told it will mess with my air fuel mixture,is that true, it’s running fine

 

If your voltage tests fine and if you do have a bad sensor, needswings.com has one:
Ambient air temperature sensor
You can check with Rob and he can verify that it will fir your car.

 

I already replaced the sensor, I'll try and replace the connector next

 

Keep in mind the new part could be defective. I have had this happen more than once.

 

The IAT (intake air temperature) sensor in the MAF (Mass Air Flow) housing is what the ECU uses to compute air density and temperature.
You can SEE this in the live data with any OBD reader that displays live data - it does not display that ambient air temperature as intake temperature varies from ambient air temperature due to the design of our intake (the intake tends to preheat the air, really poor design, that is why Needswings sells so many aftermarket intake kits).

Also, the Climate control has it's own sensors in the air flow of the heater-A/C that the climate control computer uses to operate the heat and A/C, so again, all that is there for is to tell you what the temperature of the air around is as you drive.

 

same here!

 

Wow, that’s great information, thank you