While I was trying to troubleshoot why my engine in my suburban seems to shutter a little bit at idle I noticed using my scanner that the AAT reading is -40. What sensor reports this?

The outside temperature reading on the dash still seems to work fine (it was reading 83F at the time). My 2010 Chevy Cobalt shows a proper AAT with the scan tool. Is this reading supposed to be -40? It's the only odd reading with the scan tool. There are no error codes stored or pending.

Also, would anyone be concerned with a good amount of gasoline coating the inside of the air intake. I took out the MAP sensor and it was coated in gas. My plugs that I recently replaced were also soaked in gas.

Thanks!

 

Sounds like it might be running really rich. If so, probably ruin the cat(s) before long. If the computer thinks it's running at 40*, then that would call for a rich mixture.

 

intake air temp sensor is used for fuel metering. IIRC the ambient temp sensor is just a dash display but may have an input for auto hvac.


The intake air temp is part of the maf sensor. the ambient air temp sensor is located on the left lower frame of the condenser support...behind the grille. If its reading -40 the circuit is open.

 

It's interesting, cause the IAT reading is different than the AAT sensor reading. I unpluged the outside air temp sensor and plugged my scan tool back in, then somehow the AAT was giving a reading. I've plugging the air temp sensor back in and AAT is still providing a good reading. So the outside temp sensor doesn't provide the AAT reading.

I've ordered a new MAF sensor since it does seem a bit funky and since this is an intermittent problem it's hard to track down. I'll see if that fixes the issue.

 

Its possible you just resolved it by reseating a loose connection...
What scan tool are you using?

 

I just checked the service info. you model may have 2 thermisiters. the ambient temp sensor being on the right part of the condensor support, not the left.


what are you using for a scan tool? an aat reading of -40 will set a code but it will be a body code not a powertrain code. in fact aat should not even display an aat reading under powertrain...it doesn't with a factory scan tool. regardless, it will not effect drivability.


based on your description, I would try a throttle body clean and idle relearn before a maf.

 

I have a Harbor Freight scan tool. While not the best it does seem to get the job done. It doesn't really group anything by powertrain and body and just lumps everything together.

When I plug it into my car there is one serial device it can connect to and read data from. On the suburban there are 3. 2 don't display much, but 1 displays the engine MIL codes as well as any sensor data it can pull back. The AAT is listed along with a whole bunch of other sensors in the "live data" section of the scan tool.

The sensor I unplugged was located on the front of the condenser support, passenger side (right). It's the only thermistor sensor I could located (other than the one integrated into the MAF sensor).

I will try a throttle body clean, provided I can easily get into the throttle body without too much trouble. It looks like a good amount of oil is getting in there which is probably causing issues. I read somewhere it could be caused by oil coming in through the PCV valve. We'll see once I get in there.

I also read the idle relearn can be done by unplugging the battery? Is this true or is there a service procedure for it?

 

linux2 Here is a procedure I did a while back in the DIY section, give it a read...
https://chevroletforum.com/forum/tah...-gmt900-54328/