External (Ambient) Temperature Problem

Hello all! I have a 2013 Expedition Limited. The problem I am having is, if the vehicle sits with engine off for more than an hour or so and it is hot outside, when I start the motor the External Trmperature will read 50 F. It seems to stay like that until the vehicle leaves cold loop, the the external temperature decrements until it reaches -40 F. Then, it increments up to the actual ambient temperature. During this time the HVAC will not work properly, until the displayed ext temp is sufficiently higher than the HVAC set point (as designed). The ect temp remains at the actual outside temp until the next time the truck sits for more than an hour.

I have replaced the Ambient Temperature Sensor.

Any other ideas as to what might be wrong?

Thanks!
JT

Why did you change the Ambient Temperature Sensor?

Did you preform any troubleshooting to determine that was the problem?

Your computer needs more time to register the correct temperature. Other than that, check the pigtail connector if loose.

Right, more time....

Resistive thermistor, depending on materials, respond to changes of temp in less than a second. Since you have changed the sensor the next thing would be do some diagnostic troubleshooting. How far into this do you want to go? It would require the isolation of the various sensors involved and monitor the results of "dropping" each sensor.

Bedrck47 sent me the diagrams for the climate control for the 2010 model which may be similar to your year.
This system is connected to the obd2 data requiring it to follow specific protocol rules for handling data. One of the things a module performs is to rationalize the data it receives from sensor(s). In layman terms there are 3 thermistors use to determine the temp. It compares the 3 reading to validate the input. It can't be 100 outside with the interior reading -30 and the evap reads 55. The system goes "huh"? and tosses a code.

Since yours is counting down then back up it may be a failure in one of the temp control modules programming to maintain calibration. I have a feeling these are non repairable and only can be replaced.

Thank you for the help so far!!

I changed the Ambient Temperature Probe, because I had experienced a failure on a previous vehicle and had similar symptoms. The probe isn't that expensive, so I thought it was worth a try.

I replaced it about 2 - 3 months ago, I'm going to assume that is plenty of time for the system to calibrate itself to the new probe. Plus, in cold to mild temperatures the system works perfectly. It is only when it is hot (80 and above) that the system acts poorly.

stamp 11127, I think you are correct. One of the modules is probably failing. It acts as if the memory of it calibration is getting wiped out. Leaving the system to a recalibration state after every prolonged off period (> 30 min).


Is there a test procedure or error code for the modules?

I'm sure there is but most scannerst don't include that code set. Take a look at Forscan to see if it includes the climate control codes.

You can also test the sensor if you have a dmm and heat gun. It is probably NTC type thermistor - variable resistance based on temp.. You shouldn't have any weird readings as the temp increases.