Cascadia fan comes on

My 2016 Cascadia DD16 engine fan comes on several times a day when engine is not hot but it is below freezing out.
Works normal when the ambient temp is warm out

 

No, defrost is off.
Heat us on front and back.
Yes, probably something to do with a/c.

 

Official reply from Detroit. It's supposed to do this. It's cheaper to burn the customers fuel than for Detroit to install a $90 sensor. Even though the truck has an ambient temperature sensor that I can read, I guess the engine doesn't access it.

DD ENGINES FAN RUNNING MORE IN THE COLD
reply from Scott Trippel in Tech Talk Forum - View the full discussion

We see this all the time.

The fan comes on to check the Ambient air temp.

Typically what happens is:

On the highway all is ok, truck comes to town and stops at a light. Truck leaves light fan engages. Because the truck stopped no ram air through rad and CAC. The ambient temp is calculated but turbo inlet tamp and CAC icooler out temp. The fan increases air flow and the calculation begins. The fan stops when the temp drop stabilizes.

What has happened is when stopped the under hood temp has increased the CAC and turbo inlet temps.

The calculation is required to operate the DEF line heaters.

This was a software fix.

We had trucks freeze DEF lines before because the fan was not engaging to check the ambient temp.

After the software fix a complaint of fan on started.



Usually the fan needs to run 5 to 10 min.