My 2019 Cx9 is displaying what seems to be random outside temp readings. Sometimes negative 4 F, sometimes accurate readings, but it is all over the place. When inaccurate, the climate control does not function properly.

I think this could be the temperature sensor behind the grill in front of the radiator but before I remove the bumper to replace, I thought I would post here in case anyone has had this issue and requisite insight. I also thought it could be a software issue, as sometimes the reading is perfectly accurate.

Very much appreciate the help and hope to return the favor by posting the eventual fix.

(I accidentally posted this in the new member area and would delete the errant post but I am not certain how to do so.)

 

You've probably already done it with the age of this post, but you don't have to remove the whole bumper to get to the sensor. I had the same problem, it'd drop into the 40F and colder range despite it being 90F outside. Sometime it'd right itself but overall it would be wrong most of the time driving. You can get the auto climate control to go into manual mode by turning it all the way up or down and it will display Hi or Lo instead of the requested temperature.

You just have to remove the two (maybe four) screws and then about four push pins on the top of the front fascia assembly under the leading edge of the hood. You can pull the top of the bumper towards you with one hand and squeeze the other down to the sensor and replace it. I think I disconnected the wiring through the grille and if you pull the sensor towards you it'll pop out of the christmas tree fastener holding it in. The service manual tells you to remove the whole front end, but I got away with just the fasteners on the top.

 

Depending on the year of Mazda there were ECU updates that should be done. Many times, correcting the problem.
For the original OP it should have been free and covered under warranty period both update as well if it were a sensor.

 

buttes... Welcome to the forum

 

Mine is a 2020 CX-9, and was out of the 3/36 warranty when it occurred. The sensor fixed it, and I found this late 2022 TSB: MC-10226923-0001.pdf Looks like they changed the sensor. Mine would have had a 2019 sensor, its a late 2019 build. I don't remember what the date/lot number on the sensor I replaced the original with, so may eventually have to do it again.

 

While you did not indicate I assume you verified the sensor as fault?.

As a CAUTION parts specifically sensors that report to the ECU/TCM/PCM etc., should never be randomly replaced assuming they are the problem. Many times, that will create other issues adding to the original problem. Always take the time to verify a part has failed before replacing it!

ASE

 

I did test the old sensor. It seemed to be fine if the sensor was cold but anything above 50F caused it to return a steadily increasing resistance value with it bottoming out in the 40-45F range. You could watch it on the dash as it went down, then it may climb into the 50s and then drop back down. This was all with an ambient temp in the 90s.

I didn't do any wiring checks, but I did check the new sensor as best I could. The ambient temp had dropped by the time I got the new one, but it was still above where the old one would fail. I also don't order from Amazon or eBay, just actual Mazda dealers. Its not impossible to get a fake from a dealer, just less likely. I only buy Mazda or the OEM manufacturer when it comes to electrical parts.

 

buttes

 

Calisto and buttes,

I ordered the temp sensor a week or so ago, so your postings are timely.

I continue to have the issue but have NOT tested the part. I am curious how one would do so? What would I need to test it for fault?

I was planning to try buttes suggested fix now that I see it, but I certainly don't want to cause more issues downstream.

Thank you for the guidance thus far; it is very much appreciated.

H

 

You would need a Professional level Diagnostic Scanner like a Solius to connect directly to the diagnostic connector to view the actual operation on the sensor. Not an average DIY testing. As for the sensor itself it is simply testing the resistance as per the specifications. But as you have already replaced it without first having verified the original being at fault it is unlikely all though not altogether absolute that both sensors th new and the old are both bad.

At this point instead of random testing may be to go to a shop and have them do a very basic scan and give you the assessment.

ASE