Transmission stuck in drive

2009 CHEVROLET IMPALA
153,000 MILES • 3.5L • 6 CYL • 2WD • AUTOMATIC
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ARMYVET2020
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It won't downshift manually but I can shift to park an take the key out. Once it's shut off I have to disconnect the battery for a minute or it won't crank or anything when I try to start it. The day before I noticed a slight miss that eventually went away. Would this be a bad TCM or shift solenoid? It hasn't thrown a check engine light on yet.
Aug 9, 2021 at 12:20 PM
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KASEKENNY
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Just to be clear, the vehicle only drives forward but you don't have any other gears but it will shift to park and you can remove the key? If this is the case then clearly the ECM is seeing the shift to park and releasing the interlock.

The BCM is actually what releases the interlock but clearly that is all working.

So if you have no reverse or any other gears then we most likely have issues with the valve body.

https://www.2carpros.com/articles/automatic-transmission-problems

If the vehicle goes into drive, and shifts normally then I suspect we have an internal transmission issue and not necessarily a valve body issue.

So let's start with the basics first before we just to the wrong conclusion.

First let's check for codes.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Next we need to check the fluid and make sure it is the proper level and condition.

I attached the process below from the manual on how to check the fluid.

Please let us know what you find with this and clarify me on the issue if I am not understanding.

Thanks
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Aug 10, 2021 at 4:53 PM