Ambient temp inaccuracy

[WXman]

I'm a meteorologist with a knack for calibrated instruments. I know this is very trivial but it makes my OCD flare up. While cruising down the road, my outside temperature reading on the dash is several degrees too warm compared to close-by calibrated stations. My other FCA vehicles don't have this issue. Is it common on the Rams? Will relocating the sensor fix it, or is it a programming issue?

 

[stevj]

I was thinking of relocating mine to behind the front bumper. It would then be protected from direct sun and no longer live in that black plastic outside rear view mirror housing.
I haven't been able to find a wiring diagram for it, so it's still in the stock location and takes some going down the road before it indicates anything close to ambient.

Steve

 

[BugGuy]

Yeah, I've been having a minor issue with this recently. It'll be mid 30s outside when I get in, but it registers 50s and 60s. I assume its from the sunlight. Its not too big of a deal except I'm wanting the seats and steering wheel heaters on when I remote start it.

 

[ZonaRam44]

I'm in Phoenix, AZ and it was 65* out, but my truck though it was 80* so the ventilated seat came on. Not the end of the world, but 15* off is a little much. Last summer I saw it off by over 20*. If anyone finds a fix post it up.

 

[WXman]

So the outside temp sensor is located inside the mirror housing? I thought those were usually behind the grille?

 

[Dusty1948]

So the outside temp sensor is located inside the mirror housing? I thought those were usually behind the grille?

REMOVAL AND INSTALLATION
REMOVAL

NOTE:​

Use care when removing the ambient temperature sensor in order to avoid damaging the tip of the sensor.​

1. Disconnect and isolate the negative battery cable(s) (Refer to 08 - Electrical/Battery System/Standard Procedure) .
   
   ​

   Fig 1

   
   
2. Using a flat blade screwdriver or equivalent, insert the blade in the slot and gently pry upward to remove the panel (1) located below the left rear view mirror.
   
   
   ​

   Fig 2

   
   
3. Disconnect the sensor wire harness connector (1) and remove sensor from vehicle.
4. Rotate the sensor (2) one quarter turn counter clockwise to disengage the panel from the retaining slot.

INSTALLATION

1. Position the Ambient temperature sensor to the panel and rotate the sensor one quarter turn clockwise to engage the panel to the sensor retaining slot.
2. Connect the wire harness connector to the ambient temperature sensor.
3. Insert panel with ambient temperature sensor to the lower left side rear view mirror and gently snap in place.
4. Connect the negative battery cable(s) (Refer to 08 - Electrical/Battery System/Standard Procedure) .

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Build date: 17 July 2018. Now at: 030110 miles.

 

[Dusty1948]

So the outside temp sensor is located inside the mirror housing? I thought those were usually behind the grille?

On 4th gens the ambient temperature sensor was mounted in the leading edge of one of the front fenders. I believe it was moved a few times over the course of the DS builds (2009-2019). I believe they moved it to eliminate influences of engine heat affecting the accuracy of the temperature indication after shutdown. The mirror was thought to be a better place as it's away from secondary heat sources and more in the slip stream of air currents. Mine appears to be accurate, however in the Laramie and above trips the upper mirror housings are chrome which tend to defect heat from the sun more so than the black mirror housings.
Best regards,
Dusty

2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Build date: 17 July 2018. Now at: 030110 miles.

 

[WXman]

Very interesting. Thanks for that.

I would believe that this would cause more erroneous readings than the traditional spot directly behind the grille. But this is very helpful! Perhaps on sunny days, the black plastic of the mirror is radiating heat into the sensor leading to the bad readings. Knowing is half the battle. Thanks!

 

[mike_ct]

In the morning, depending on how I park in my driveway, if I get morning sun on my driver mirror, it will often read 50-degrees outside when its 30, so I don't get heated seat with my remote start, which sucks! In my truck, the outside sensor is in the driver side mirror, underneath near an edge. its just an exposed thermistor with a black coating on it.

 

[mikeru82]

On 4th gens the ambient temperature sensor was mounted in the leading edge of one of the front fenders. I believe it was moved a few times over the course of the DS builds (2009-2019). I believe they moved it to eliminate influences of engine heat affecting the accuracy of the temperature indication after shutdown. The mirror was thought to be a better place as it's away from secondary heat sources and more in the slip stream of air currents. Mine appears to be accurate, however in the Laramie and above trips the upper mirror housings are chrome which tend to defect heat from the sun more so than the black mirror housings.
Best regards,
Dusty

2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Build date: 17 July 2018. Now at: 030110 miles.

Both of the 4th gens I have owned (2015 Tradesman and 2017 Rebel) had the sensor mounted in the driver side mirror. All three (including my current 2020 Laramie) read high if parked such that the mirror was in direct sunlight, no matter what time of year. My commute is about 25 minutes of highway driving, and after about 5 minutes driving the ambient temp appears to be accurate. This behavior has been consistent for all three of the trucks.

 

[yellowboy]

Mine is always off - always higher than actual temperature. The warmer it is the more it's off. Sometimes 6-7 degrees. I Have it on the list for dealer so I can hear " it seems to be working within specs " again …....

 

[bigoldthor]

Maybe the rest of the world's temperature readings are too low and the Ram's are just right.

 

[Eltaco]

Mine was off by 40 degrees today. Parked in the garage, drove it out into 52deg weather and the display told me it was 92deg out. Stayed fixed at 92 for 15 miles, turned the truck off and it sat for about an hour, and when I started it back up, it was still on 92 until I got home.

I’ve had the truck for 2 months and already have two recalls and a TSB to take care of. Guess I’ll just add this to the stack for when I get my first oil change.

 

[OldMarine]

When I first got my 2019 one of the first things I did was remove the temp sensor, waited 5 minutes, and reinstalled. It's been accurate ever since. I highly recommend trying this first.

 

[yellowboy]

How did you remove it ?

 

[OldMarine]

How did you remove it ?

It's under the driver mirror housing. Need a tiny flat head screw driver to pry off the cover then you will look in and see the sensor.

 

[WXman]

After more time has passed, what I'm noticing is that on sunny days, it never does equalize to the point of being accurate. This is what I'd expect, seeing as how black plastic absorbs solar radiation very effectively. Whoever at FCA decided to put the ambient sensor in this location is a moron. Behind the grille was a much better spot because it was shaded, and the engine heat was on the opposite side of the radiator/fan so that wasn't ever really an issue.

I guess this summer when I get bored I'll look into moving the sensor to a better spot maybe.

 

[Eltaco]

I’ll try disconnect/reconnect mine to see if it resolves, but I’m confident my issue of 40deg in accuracy wasn’t related to solar gain since I had my truck stored in the garage.

Yes, black box solar gain is a real issue for all electronics. I’m not sure where the temp is taken on other vehicles, but I’ve never encountered this inaccuracy on previous vehicles (Toyota’s).

I’m not sure what would be involved with moving the sensor. That sounds like a major PITA.

 

[OldMarine]

the reason I knew to do the disconnect-reinstall trick, was someone else on here did it and said it worked. So I did it, and sure enough, worked like a charm.

 

[Eltaco]

the reason I knew to do the disconnect-reinstall trick, was someone else on here did it and said it worked. So I did it, and sure enough, worked like a charm.

Thanks. I sort of hate just hiding the issue with resetting the sensor if there’s a fault there, but I’m only 3700mi in to ownership so have a lot of warranty left.

More than anything, I hate going to the dealer more than necessary. This one is sort of aggregating since it automatically starts my ventilated seats, even tho it was 35deg out this morning. Stupid complaint, but just involves more button clicks that shouldn’t need to occur. Haha