Today I pulled my 2017 RX350 from the garage into the 90-degree heat. Despite driving about 10 miles, the outside temperature only inched up from about 72 to 75 degrees. Since it is giving a reading (though inaccurate), I'm wondering if the sensor needs to be replaced or does something need to be reset. This happened to me twice on my previous generation RX and I replaced the sensor twice. I think each time it worked for a while and then failed. I couldn't find a link on this in the Forum so I am wondering if this is a common occurrence. Also, could someone confirm that the correct part number for the 2017 RX350 is 88790-06020. Thanks!!!

 

Wow.... That just happened to me TODAY!

 

The temp. sensor is actually a "thermistor" which is a variable resistor changing its resistance value as the temperature changes. Not a real sturdy piece of equipment. They cost about 10 cents to manufacture. Of course Lexus will charge you about $41 for one. The main computer relies on the temp. info to operate the automatic climate control system. More details here:
https://www.yourmechanic.com/estimat...ch-replacement

 

Thanks, but your link is only to an ad to have "Your Mechanic" replace the sensor for about $150. The sensor is very accessible by the radiator and only takes about 5 minutes to replace. I just ordered one from MyLparts.com using the CL5 discount code for $44.86 including shipping.

 

Sounds good. When you receive the new part and uninstall the old one, I would be interested in a side by side comparison. Is the new one an OEM part? Is there a part number stamped on them? etc.
Please let us know how everything works out.

 

I needed a very small pliers to remove the old one since you need to press in the 2 small plastic tabs to release the unit from the metal hole. It's located in front of the radiator, but lower down. It is an OEM part. All it has imprinted on it is "1 of 13" and "Japan" (reminds me of seven of nine from the Borg). It was identical to the one I removed (see picture of removed part and the new part package). I haven't driven the car yet to test it but will let you know if it does not work.

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The thermistor mounted in front of my radiator on my 2017 RX350 is once again not working. Outside at 85 degrees it reads 73, then slowly moved to 75. Same thing happened 2 years ago (see my posts above) and also happened a few times with my previous RX. Lexus builds bullet-proof cars and yet this simple $45 part, a variable resistor, fails when all of the millions of semiconductors in our cars perform well for many years. This part appears to be in most Lexus/Toyota cars. Lexus: spend 50 cents instead of 25 cents and manufacture a reliable temperature sensor. BTW, does anyone know if this sensor affects the air conditioning? I have not noticed a difference, but the parts descriptions suggest it might.

 

It is strange, we had / have 2 RX's and none of them experienced what you are experiencing.

 

thats odd. have you tested the sensor? heres the chart if you need it. I would just grab one from a junk yard, you might get an older (better quality) part. just cross ref. the PN.

 

The sluggish response of the outside air temperature sensor has been discussed on here before. While it is possible of course that a sensor has gone bad, in general RTDs are pretty reliable. After all, they are merely simple passive devices. Other factors may’ be coming into play here. First, the sensor’s mounting location. The area where it is mounted does offer a fairly high “thermal mass” and so it may take a while for the stuff around it to get up to temperature. Moving at highway speeds should help. Second, I strongly suspect the computer processes the sensor’s reading with a PID loop. The reported temperature may thus be the result of a smoothing algorithm and therefore take a while to read more realistically.

I do not have any insider information of course, but from what I can see, the outside air temperature only affects the climate control system’s decision to open or close the outside air damper. In other words, whether to recirculate the cabin air or draw in outside air in Auto mode. This can be over-ridden manually by switching to either recirculate or draw in outside air if desired. Personally, I almost always leave it on auto, even here in Phoenix. The one exception: there’s occasions when I pass by a cattle yard locally, and if I see it has gone to outside mode, I switch it to recirculate instead until I have gotten out of nose-shot.

Main takeaway: for me, unless the reading has gone completely bonkers (reading 30 degrees instead of an expected 110) I wouldn’t bother with it. But 95 instead of the expected 110? I would see what it reads after an hour and even then…probably not mess with it. YMMV, batteries not included, objects may be closer than they appear, the other usual disclaimers…

 

Thanks everyone! I agree that it is a completely passive device. But it has happened to me 3 times in 2 RX's in the last 10 or so years. I'm still amazed that this has not been frequently reported in the forum. This time, probably like in the past, I took the car out from a pretty cool garage into the hot and humid outside. Makes me think that perhaps there was some sort of condensation that affected the wire connector contacts. When I've fixed the problem in the past with a new senor, perhaps it was just the making of a fresh new contact that did the trick. I'll do nothing for a while. If still a problem, I'll try disconnecting and reconnecting the existing sensor. Will keep you posted.

 

Looking at the chart that was posted…that’s a pretty significant tolerance. Like plus or minus 10 percent resistance for a given temperature.

If you have contact cleaner like Deoxit, it’d be worth trying to clean the connection there. Put a little into the female side, then plug and unplug a few times. Then before the final reconnection put some silicone dielectric on it (avoid the pins or female holes, if possible) then plug it back in.

 

Hi, would you mind snapping a pic of the location of the sensor? Tried to find it, but just wanted to make sure I was looking at the right thing. Thanks

 

I opened my hood to take that picture and was then reminded that I would have to remove that large black plastic cover in the front. A bit of a pain with all those plastic pins. Easy to lose one. The sensor is mounted very close to the front of the radiator, perhaps an inch of so away. Once you remove the plastic cover it is pretty obvious since there is nothing else in front of the radiator.