Rear View Mirror Temp Display 10* High

[tscott0000]

Hi Folks,

 

This is my first thread, please excuse me if this topic is over done.

 

My Outside Air Temp Display on my rear view mirror (Onstar,Temp,Compass) shows approx. 10*F higher than actual (based on weather reports, my wife's VW and bank temp displays). I've changed out the sensor (the one in front of the radiator on the cross bar) but there has been no change.

 

Is there a reset/calibrate/reprogram method to this? If not, what other options are there?

 

Thanks,

TScott

[email protected]

2004 Sierra Denali Quadrasteer

[Zembonez]

I think it is a good question.

 

It's a rather funky car feature and not all that well designed. The sensor picks up radiant heat from the vehicle and skews the reading. Not really sure how to get around it. My GM, Honda, and Nissan vehicles have always done this. The reading is somewhat more accurate when highway driving but in city stop and go, the reading is way off. With hot road surfaces and the heat generated by vehicles, I don't see how there will ever be an actual temp display.

[Fireman Ed]

I know on my wife's Aztek the sensor is right in front of the radiator. I would think that there would be a better place for it somewhere, but once you are moving it seems to be fine. I haven't looked for it on my new truck, but I guess that it is probably the same.

[98silvz71]

John Kennedy has a solution to this. He moved the sensor away from the radiators to limit the amount of heat it soaks up from them.

 

Hope this helps.

 

Temp Sensor Relocation

[minibike132]

I have rarely ever seen location of the sensor be the issue. If you replace the sensor the module does need to be recalibrated. If the engine has been off all night and it is +10degrees at key up how can location relative to the radiator be the issue. Following is the circuit description quote.

 

The ambient air temperature sensor mounts underhood and can be affected by city traffic, by idling, and by restarting a hot engine. Therefore, the HVAC control module filters the value of the ambient air temperature sensor for temperature display. The ambient air temperature value is updated under the following conditions:

 

Condition

Display

 

At start up with the engine off less than 2 hours

Displays last stored temperature

 

At start up with the engine off more than 2 hours

Displays real-time temperature

 

Engine coolant temperature is less than 28°C (50°F) above the ambient air temperature

Displays real-time temperature

 

Vehicle speed above 32 km/h (20 mph) for a minimum of 80 seconds

Displays real-time temperature

 

Vehicle speed above 72 km/h (45 mph)

Displays real-time temperature

 

Sensor reading is less than the last displayed value

Displays real-time temperature

 

 

The scan tool has the ability to update the displayed ambient air temperature. To update the ambient air temperature display on the HVAC control module, perform the following procedure: Simultaneously press the MODE, FRONT DEFROST and REAR DEFROST switches.

 

Turn ON the ignition.

Simultaneously press the MODE, FRONT DEFROST and REAR DEFROST switches.

 

The module does know how hot the radiator is and is designed to filter that out. Perform the sensor update and if it is still off there is a circuit issue. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor signal voltage decreases as the resistance decreases. Therefore if you are reading high then there is less resistance than there should be in the circuit or the module isn't interpreting the signal correctly.