Ambient Temp Sensor Not Reading Correctly After Wiring Repair

Michael Mobile Technician Clinton, Utah Posted   Latest  
Discussion
HVAC
2013 Chevrolet Spark LS 1.2L (9 LL0) 5-spd (Y4M HD)
No A/C
Ambient Temp Sensor Reads -40

Just a quick note on the Chevy Spark. A shop owner told me last week he had done a wiring repair on the ambient temp sensor. It was reading at -40 preventing the AC system from operation. He told me that the sensor had to be reset. I thought maybe he had rolled a fat boy before calling me over to "reset" it. Sure enough, the sensor read -40. A trip into GDS2 revealed a ambient temp reset in the instrument cluster. Sometimes I think the engineers do this on purpose.

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Dean Owner
Albany, New York
Dean Default
 

Good to know Michael. Thanks!

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Mario Diagnostician
Weston, Florida
Mario Default
 

Thanks for the heads up!

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Richard Instructor
Palmetto, Florida
Richard Default
 

Many of the new Fords require this also. Some may reset after a cold soak.

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Andrew Technician
Commack, New York
Andrew Default
 

I have a guess as to what's going on. See the attached screen cap from a GM document. "a high inrush current to fire off the bulb. When this happens, the control module shuts down the output driver. It’s not because the output driver can’t handle the temporary current spike (up to half an amp), but because the control module’s software is calibrated to turn off the output driver at a very low…

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Richard Instructor
Palmetto, Florida
Richard Default
   

I doubt that is the case Andrew. The ambient temp sensor reports a wildly fluctuating temperature during normal operation. If the car is going down the highway or stuck in traffic the ambient temperature sensor could read drastically different. So the module Filters the displayed value. After sitting for some time or getting the car up to highway speeds, the ambient temperature will be displayed…

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Andrew Technician
Commack, New York
Andrew Default
 

Which part do you doubt exactly?

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Jim Curriculum Developer
Frederick, Maryland
Jim Default
 

True. You can even see it on some vehicles looking around for ambient temperature PIDs in different modules. Some will be listed as Raw values and others as filtered and not necessarily in the module the unit is wired to. Description and operation strategies are also interesting. We will find that the strategy to LOWER the temperature reading will happen instantly when detected on a vehicle…

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Andrew Technician
Commack, New York
Andrew Default
 

Here's my second note regarding the -40 reading, which was likely but not necessarily displayed in Celsius. Temperature sensors will have different ranges (compare evaporator, intake air, coolant, and exhaust temp behaviors) and different precision - the intake air temp affects combustion whereas the ambient temp is more of a comfort issue. In the control module a temperature may be stored and…

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Jim Curriculum Developer
Frederick, Maryland
Jim Default
 

Good point. My reply was in general strategy as well. To your point. the -40F/C reading is such a normal "open circuit" default one can get used to looking for it. Even TPMS will display that value in tire temp with a faulty sensor. I was going to demonstrate this on a 2010 Ford Flex only to find out.......NO. On open ambient sensor on that vehicle would display a default 50 degrees F! If you…

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Andrew Technician
Commack, New York
Andrew Default
 

Exactly, -40 is a common one. There are some others that you may get to know if you work a given application a lot. Some powertrain sensors are using a 3.3 instead of a five volt reference too so there is some variety.

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Caleb Technician
Mishawaka, Indiana
Caleb Default
 

Thanks for this. Actually had a 2014 Fusion tonight with p0073 ambient temp sensor open and 50° displayed on the readout. It was a stupid diag tho. The entire front fascia harness, ambient temp sensor an active grille shutter assembly were missing.

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