Ambient air temp sensor inaccurate

[zmnypit]

I replaced both the sensor in the mirror and the one behind the grille on my 15 Sierra 2500 duramax and it's still reading inaccurate. Take today for example, it's 91* here and when I pulled out of the basement the dash temp will read correctly for a min then it steadily declines once driving until it reaches 33-55* (this seems to be it's sweet spot). Do I need to reset them somehow? Or is there another sensor I'm missing?  Never had this problem in my 1500 and it wouldn't be an issue if it didn't confuse my A/C. I like to keep it on auto 69-70* but doesn't cooperate when the dash is thinking there's ice out. 

[redwngr]

Mirror sensor is used by the duramax engine control. (gassers don't have that one)

 

Grill sensor is for the dash display.  

 

While driving, does it ever recover to correct temp?

Could it have moisture on it that is evaporating causing the low indication (swamp cooler effect)?

 

They grill sensor display is programmed to change slowly so that it doesn't swing wildly with every time vehicle is stopped/slowed for a short period. 

 

 

[newdude]

Test.  Having forum issues.  Keep running into CATCHPA issues.  

[newdude]

 

Quote

 

#PIT5365C: Diagnostic Tip - Ambient Temperature Display / Information (Topology) - (May 21, 2015)

 

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern

There has been some confusion on how the temperature reading that is displayed on the radio, gets from the ambient temperature sensor to the actual radio display.  Depending on the model and radio option, it may vary. The block diagrams below should help clarify any confusion.

 

-1500 Trucks and All SUV's With IO3 Radio

Ambient Air Temperature Sensor >>> (hard wired circuits 636 and 61) >>> ECM >>> (High Speed Lan)>>> BCM >>> (Low Speed Lan) >>> Radio tuner >>> (LVDS Cable) >>> Radio Display 

 

-1500 Trucks and All SUV's With IO4, IO5, or IO6

Ambient Air Temperature Sensor >>> (hard wired circuits 636 and 61) >>> ECM >>> (High Speed Lan)>>> BCM >>> (Low Speed Lan) >>> Radio tuner >>> (MOST BUSS) >>> HMI >>> (LVDS Cable) >>> Radio Display 

 

-2500/3500 Trucks With IO3 Radio

Ambient Air Temperature Sensor >>> (hard wired circuits 636 and 61) >>> IPC >>> (Low Speed Lan) >>> Radio tuner >>> (LVDS Cable) >>> Radio Display

-2500/3500 Trucks with IO4, IO5, or IO6

Ambient Air Temperature Sensor >>> (hard wired circuits 636 and 61) >>> IPC >>> (Low Speed Lan) >>> Radio tuner >>> (MOST BUSS) >>> HMI >>> (LVDS Cable) >>> Radio Display 

 

Important: For all 2500/3500 radio combinations listed above, some early built 2015i trucks (RPO AVF = 2015i mid year change) equipped with 6.6L diesel engine (RPO LML) built before 12/14/14 use the ambient air temperature sensor located in the passenger mirror for the temperature displayed on the radio, HVAC and powertrain requirements. If the BCM and IPC are reprogrammed with the latest calibrations in TIS2WEB, this will change the operation of the radio and HVAC topology to what is shown above. This is how these trucks built since 12/14/14 come programmed.  The grille mounted ambient air temperature sensor will now be used for the radio and HVAC requirements, and the passenger mirror sensor will now only be used for powertrain requirements. The radio outside temperature display will show "- -" if only one of the modules (BCM or IPC) is programmed with the latest calibrations. The other module will need to be programmed with the latest calibration to correct the issue. The 2015 6.6L diesel trucks (RPO LML) built PRIOR to the mid year change 2015i (i.e. NOT equipped with RPO AVF) do not use a physical ambient air temperature sensor in the passenger outside mirror for the powertrain requirements. The outside temperature for powertrain requirements is calculated by the ECM. The radio outside temperature display and HVAC requirements will still follow the 2500/3500 topology listed above.

Note: For all the 1500/2500/3500 radio configurations listed above, after the IPC or BCM sends the ambient air temperature out on the Low Speed LAN buss, the HVAC control module will use this information for HVAC related requirements.

 

 

[zmnypit]

On 8/2/2018 at 11:15 AM, redwngr said:

 

 

While driving, does it ever recover to correct temp?

Nope. Drove maybe 30min today on lunch and temp would never get about 62* on the dash while its 97* outside. 

[zmnypit]

On 8/4/2018 at 1:35 PM, newdude said:

 

 

So I need to have it re calibrated? 

[jwstewar]

I can't help the original poster, but I can add some confusion to how the outside temp sensor works

 

When I first bought the truck I swap the regular mirrors for tow mirrors. I didn't know about the temp sensor. Got the check engine light. The dash display worked fine. Put the original mirrors back on. Check engine light went off. Temp on the radio displayed -40 and the start up screen said watch for ice. About 10 minutes after driving, the temp on the display started going up and was fine. Ordered an ambient temp sensor from boost auto parts and installed into my tow mirrors. Installed them back on the truck. No check engine light, truck displayed message to watch for ice, radio displayed -40 degrees. Drove about 10 minutes, temp on the radio started going up and has been fine since.

[zmnypit]

I'm still fighting this issue. Today was 73* and dash display was saying -6*. Not sure what else to do other than take it to the dealership.