Is Transmission Temp Check Mode Necessary?

FYI - On my 2021, I was trying to use a jumper wire to get it into temp mode. Took me a little while to realize that year doesn’t need the jumper to go into trans check mode. I’m wondering if a 2020 was the same and maybe why it was hard to get into.

Regardless if you have a scan tool it’s easier.

 

The 2020 doesn't need the jumper wire but I still had issues getting it to work. I watched a couple of videos including the Car Care Nut.

 

That was my next question. Thank you

 

Now that i’ve done drain and fill a couple times and know its at the right level,’ i was thinking of just adding the same volume that drains out and not checking the overflow plug….
After the factory level question is answered, if you drain 2.5….add 2.5 lol

 

That makes perfect sense to me. That's exactly why someone will post that I shouldn't do it that way because of this or that. They'll be right and I'll once again go back to electronics and databases where my expertise really is and leave this to the experts. LMAO!

 

It matters a lot. The difference between check temp and normal operating temp fluid level is significant.
For some reason ATF expands much, much more than motor oil. I don’t know the specifics as to why but it does.

 

Negative.

I can confirm this.
I think my external IR reading 5° under the gauge.
Plenty close enough.

 

I was reading the official service procedure. It's really confusing. Even if you use Techstream they still want you to put it into temp check mode??? Makes no sense. The other thing I noted was this in regards to disconnecting from Techstream:

"Be sure that terminals TC and TE1 are not connected. If the terminals are connected, the fluid level cannot be precisely
adjusted due to fluctuations in engine speed. Disconnecting terminals TC and TE1 activates engine idle speed control mode."

The Car Care nut says a scan tool is fine so that's what I'll do but it's interesting that the service manual wants you to do both. This is what gave me pause about temp check mode.

 

even 10 degrees isn't really significant. If your gun reads 100-105, do the proceedure and call it good. Were only talking about a few ounces difference here