GMT900 Outside Temp Display Weird Programming

aflesch · February 10, 2014

So I have noticed something weird about the way my outside temp display behaves. The company I work for has multiple buildings in the same industrial park and throughout the day I have to drive between them several times for various reasons. I started noticing that sometimes the temp display would update and sometimes it wouldn't. Sometimes after 3-4 trips throughout the day (sometimes running for almost and hour while I was inside) it would still read the temp that it showed when I arrived at work at 8am; but other times it would read the current temperature.

I started paying very close attention to when this would happen and here are my findings:

If the truck has not been sitting with the key out of the ignition for more than 3 hours, the temp display does not update until you have driven 3 miles.

I know this sounds really weird but it does this consistently. So when I would make 3 or 4 trips during the day (none more that 3 hours apart) the temp would not update from the 8am temp until I was 3 miles from work on my way home.

I think the weirdest part is that there is no time override. Meaning, no matter how long the truck sits and idles the temp still will not update until I have driven 3 miles.

Has anybody else noticed this in their truck?

Shaners · February 13, 2014

Mine seems to be very slow to recognize the true outside ambient temp too. I am going to have the dealer look at it this spring.

MaverickZ71 · February 13, 2014

I too have wondered about the outside temp sensor module and its programming.

I've seen times when mine instantly jumped up to an incredibly high number (say like 125F when it was 95F out) and then take a few miles to back down in the hot summertime. I assumed it was 'heat soak' in the underhood sensor. [but then I've not noticed any other vehicles that I've driven doing this kind of thing.]

I've also seen times during cold wintertime when the reading starts 20 degrees high (as compared to local weather report) and then it takes a looonnngggg time to adjust to the true temp, say like over a 2 hour trip to adjust to the correct temp.

Mentioned it to my service manager before the bumper to bumper warranty expired and he said it was ok--as long as it was reading a temp number, GM wouldn't replace the sensor.

I guess it's not much of a problem unless the PCM somehow uses the outside temp reading to adjust the engine tune and shifting and it's not right.

I just thought of another thing--my truck has the automatic climate control (where you set the interior temp at like 70F and it does what it needs to do to hold that temp.) Last fall my outside temp reading in the DIC was stuck for 3 days at 31F (following a string of days where the high was 30F or so) after it warmed back up to 62F (crazy weather around here the last couple of years). When it was stuck on 31F, the climate control had the heater on when it was 62 out, and when I put it on manual mode, even then I could not get the a/c compressor to turn on, because the climate control unit thought it was freezing out. I wasn't too happy when business-related passengers asked why it was hot inside and I had to tell them 'because my $40K truck doesn't always work right!'

Sir Dan · February 13, 2014

I too have wondered about the outside temp sensor module and its programming.

I've seen times when mine instantly jumped up to an incredibly high number (say like 125F when it was 95F out) and then take a few miles to back down in the hot summertime. I assumed it was 'heat soak' in the underhood sensor. [but then I've not noticed any other vehicles that I've driven doing this kind of thing.]

I've also seen times during cold wintertime when the reading starts 20 degrees high (as compared to local weather report) and then it takes a looonnngggg time to adjust to the true temp, say like over a 2 hour trip to adjust to the correct temp.

Mentioned it to my service manager before the bumper to bumper warranty expired and he said it was ok--as long as it was reading a temp number, GM wouldn't replace the sensor.

I guess it's not much of a problem unless the PCM somehow uses the outside temp reading to adjust the engine tune and shifting and it's not right.

I just thought of another thing--my truck has the automatic climate control (where you set the interior temp at like 70F and it does what it needs to do to hold that temp.) Last fall my outside temp reading in the DIC was stuck for 3 days at 31F (following a string of days where the high was 30F or so) after it warmed back up to 62F (crazy weather around here the last couple of years). When it was stuck on 31F, the climate control had the heater on when it was 62 out, and when I put it on manual mode, even then I could not get the a/c compressor to turn on, because the climate control unit thought it was freezing out. I wasn't too happy when business-related passengers asked why it was hot inside and I had to tell them 'because my $40K truck doesn't always work right!'

That is strange. It sounds like there could be a problem with the sensor(s) there. On my 08, the outside temp and the HVAC ambient temp are two seperate sensors located in front of the radiator. I also have the temp/compass in the rear view mirror which I much prefer over the newer trucks in the DIC cluster.