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- '17 CX-5 Select
I dug around a bit to locate the ambient temp sensor (in front of the AC condenser to the right of the grill M emblem, looking into the grill). A good spot for the sensor to read ambient air once the car is moving above 15mph or so.
Traced the sensor wires, where they wrap around the air snorkel and into a wire loom . See photos. Used a razor knife to cut through the tape, then parted the loom, and pulled out the green wire. The sensor wires are brown and then green w/ white band. I cut the green wire and soldered in a 500 ohm pot so I could make adjustments.
From the 2016 CX-5 shop manual, they publish the thermistor curve, which I assume is the same for 2017+. Variations in thermistor tolerance most profoundly affect temps above 60F or so. My thermistor read noticeably HIGH at 75F or hotter. I'm currently adjusting for dead on at 85F (pot adjusted to ~ 159 ohms), which should make it read +/- 2 degrees of actual from about 15F to 95F. Will likely read about 2F HIGH at 15F and 3F LOW at 100F. By 105F it may read 4F LOW, if my sensor follows the predicted curve. In any case, more accurate than it was originally (7F high at 100F). The Mazda allowable tolerance is 9F at 100F.
I could further improve accuracy over a larger range by using a 150 ohm NTC thermistor (nominal value at 77F) instead of a pot, and locate the thermistor in the grill air stream. Unless my fixed resistor (pot) solution proves unacceptably inaccurate when it's 110F in Texas, I'll probably leave the simple fix.
If your sensor tends to READS lower than actual as the temps get above 75F, the pot/resistor trick wont work for you.
Traced the sensor wires, where they wrap around the air snorkel and into a wire loom . See photos. Used a razor knife to cut through the tape, then parted the loom, and pulled out the green wire. The sensor wires are brown and then green w/ white band. I cut the green wire and soldered in a 500 ohm pot so I could make adjustments.
From the 2016 CX-5 shop manual, they publish the thermistor curve, which I assume is the same for 2017+. Variations in thermistor tolerance most profoundly affect temps above 60F or so. My thermistor read noticeably HIGH at 75F or hotter. I'm currently adjusting for dead on at 85F (pot adjusted to ~ 159 ohms), which should make it read +/- 2 degrees of actual from about 15F to 95F. Will likely read about 2F HIGH at 15F and 3F LOW at 100F. By 105F it may read 4F LOW, if my sensor follows the predicted curve. In any case, more accurate than it was originally (7F high at 100F). The Mazda allowable tolerance is 9F at 100F.
I could further improve accuracy over a larger range by using a 150 ohm NTC thermistor (nominal value at 77F) instead of a pot, and locate the thermistor in the grill air stream. Unless my fixed resistor (pot) solution proves unacceptably inaccurate when it's 110F in Texas, I'll probably leave the simple fix.
If your sensor tends to READS lower than actual as the temps get above 75F, the pot/resistor trick wont work for you.