Hey guys i have a 07 silverado max 6.0 and anytime the computer sees some sort of problem and sets the check engine light off or stabiltrak light it shifts hard from 1st to 2nd but the second you clear the code it shifts normal! Ive worked in a few repair shops in my day and seen many vehicles in various makes and models with a check engine light on and many stored dtcs and never had them cause the vehicle to shift hard unless of course the problem was related to the transmission.

I have read all over the internet of people with gm trucks around the same year (07 08 09) complaining of hard shifting when the check engine light comes on even if it is something as small as a evap leak or somthing along those lines that should no way affect how the vehicle shifts. So anytime my truck throws a code for anything the truck will shift super hard from 1st to 2nd and as soon as you clear the code it shifts like new. Now obviously i understand that any issue causing you check engine light to come on should be addressed but it shouldn't cause the truck to shift like that for something like a loose gas cap or something small

can anyone explain why this happens on these trucks.........thanks for your time

 

I would suspect it's because it goes into a safe mode and probably shifts at predetermined points. Once it sees everything is normal it shifts normally.

 

what he said. the trans enters failsafe and boost line pressure to protect from a detected slip condition.
what code is setting

 

 

if the stab light is on...codes are set...but you will need a scan tool that can access chassis codes to retrieve them.