No down shift on 02 Montana

02 Montana with 4T65E electronic 4 speed transmission. car has 75000 miles. normal driving and shifting seems to be fine. transaxle will not downshift with accelerator pedal pressed to the floor. no check or service engine lights.

Your best bet is to make sure that it’s insured and leave it someplace seedy. Those vans suck - like really badly. As do those 4T65Es. Or - since some will object that that judgment - I’ll say that one of GMs problems over the years has been inconsistency. Some people don’t have much trouble with those vans or those transmissions and like them. But when there is trouble, you might as well shoot the thing. So if you’ve liked it so far, then assume it is all downhill from here. [Sorry - recovering owner of a 2000 Silhouette - have you ever seen anyone cheer at a blown head gasket? That was me - an excuse to get rid of that POS]

Anyway. Unfortunately, you probably do have error codes in there even though there are no warning lights. GM is big on that for some reason. The transmission error zone can be lit up like a Christmas tree and unless you put a special Tech II scanner on it you’d never know there were any codes at all. So you will have to cough up the $$ to have it scanned by someone with the right equipment. If you want to do that and come back for help be sure to report the exact error codes as shown by the scan, and fill people in some more on the van and it’s maintenance history. E.g. has the trans ever been serviced (pan & filter)? Did you at least check the fluid? Etc.

If you want to tinker, there are basically 3 things responsible for telling the computer that you’ve floored it: 1) throttle position sensor (easily tested even with just a basic electrical meter); 2) MAF sensor; 3) MAP sensor. Best to have a scantool for the last two, but can also be tested with a basic meter.

You should also report more than that there is “no downshift.” Be more descriptive - it’s the internet. You might be thinking “downshift” but maybe not. Describe exactly what is happening (what you see / hear / feel…etc)