Hey JOSHUA808,
A great place to start would be to check for codes, guide below to check for engine management codes but the same process will give you transmission codes.
https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing
Also another thing to check initially will be the transmission fluid level/condition.
This is the always the first thing to do with an automatic transmission. Faults caused by fluid level, poor fluid condition and blocked transmission fluid filters are very common and you have to rule this out before diving into the control system.
There will be instructions on how to check/top up the fluid in your owners manual.
Generally you check the level with the engine at operating temperature, engine running, transmission in P.
If you have to top it up start with small increments and work your way up to avoid over filling. Make sure you are using the right fluid for your vehicle.
If the fluid looks dark and you have not had a fluid and filter change done then you will need to do this and retest.
Regards, Joe
Friday, June 25th, 2021 AT 12:48 PM
(Merged)