Outside air temp sensor reading low...

[vettewine]

My '99 convertible C5 outside air temp sensor has always read low since new and the problem seems to be in the receiving end of the circuit. I have replaced the sensor itself (located below the radiator mount on passenger side) twice and still get an inside readout on the a/c info screen that seems to be between 10 and 14 degrees too low. Anyone with any ideas on how to calibrate the inside readout for the sensor as the sensor itself seems to be OK?

[c4c5specialist]

HI there,
Check the temperature sensor CONNECTOR itself.
Moisture intrusion can turn the terminals green with oxidation.
Allthebest c4c5

[vettewine]

I cleaned the connector terminals both times that I replaced the sensor itself. I am getting a readout that goes up and down when the temperature outside changes but it's just not reading the temperature correctly - always about 10 to 14 degrees too low.

[irfgt]

Disconnect the battery for a minute or two and see if this corrects it.

[vettewine]

I've had this vehicle for several years now (it had 9800 miles on it when I bought it) and I've disconnected the battery more than once and replaced the battery one time. The outside temp reading is, and always has been, low by about 10 to 14 degrees F. This is not something that just occurred but it's been a thorn in my side for several years. Thanks for the suggestions, though...

What I'm trying to find out is if there is a place on one of the circuit boards where one can adjust (tweak, calibrate) the readout from the sensor...??? This may not be possible if the circuit is calibrated at the manufacturer or supplier and I may just have to tear into it and play with it myself...

Any ideas or suggestions are more than welcome...

Thanks!

[c4c5specialist]

HI there,
Actually, no, there is nothing to calibrate.
So, the basic course of action is 2 fold.
#1, make sure you have 5.0 volts being sent TO the sensor.
#2, make sure the signal out of the sensor is reaching the module.
This requires an ACCURATE DIGITAL VOLTMETER.
Do you feel your up to the task?
Allthebest, c4c5

[vettewine]

I can check the sensor input voltage OK but where is the module located to check the output of the sensor and what should it read? Thanks...!

[c4c5specialist]

HI there,
The what it SHOULD READ is based on temperature, nothing else.
So, that being said, the reading will fluctuate based on that factor.
So, what you would do, is test the Light green/black wire for 5.0 volts at the SENSOR once it is unplugged.
Simply touch the red to that wire and the black lead of your voltmeter to the Grey/black wire at the connector.
That will tell you if you have a good voltage source and ground.
Tell us what you get.
Allthebest, c4c5

[vettewine]

Gotcha...! I'll check that and get back to you... Thanks!

[vettewine]

OK, I disconnected the outside ambient temp sensor connector and read the voltage across terminals: it read +5.6 VDC. The terminals have always appeared clean and in good condition before so I had always just given them a cursory cleaning. This time I brushed them well, blew clean air on them from an dry air cannister, sprayed Contact ReNu (contains freon TF and is made for cleaning electronic contacts) and replaced the connector. Then I turned on the ignition key, waited a few seconds for the outside reading to appear and it read 54 degrees F. The engine had been off for more than 3 hours so the readout should have been the current ambient outside temp which was 55 degrees F. "Eureka!" I am very happy with only 1 degree of error so thanks to you "C4C5Specialist" for making me go back and check it out thoroughly and correctly!

This is, by far, the best forum for 'Vette aficionados on the web...!