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Discussion Starter · #1 ·
My G8 is a V6 model. I thought my motor was sputtering, but I've come to realize my car is having issues when it's trying to downshift. It feels like it's jumping back and forth between the gear it's in and the gear it's trying to downshift too. I changed the filter and fluid earlier this year.
 

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Sorry to hear. Does this happen with every gear or limited to only a specific gear? Does it happen every gearshift or only under certain conditions? Are you confident the fluid level is correct?
 

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Discussion Starter · #7 ·
I found this response for a similar issue on a Cadillac forum.

"Over time the transmission module adapts to the characteristics of the driver. This adaptation resets to defaults if the battery is disconnected. This explains why trouble started when you changed the battery. As time goes by your transmission module is undergoing the relearn process. The sticker is that apparently your TCM has corrupted programming. Best case is that it relearns in a good way and the problem eases. Worst case you'll have to have the TCM reflashed or replaced."

I'm going to give this relearn procedure a try. GM 5L50 adaptive learn.pdf
 

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Very well. Had a similar issue on the former G8. Took it to the dealership and said something going on with the transmission. Perchance being warranty work they said we can't find anything wrong with it. Few days later while driving on the freeway the car wouldn't go over forty miles per hour. Took it back to the dealership and the planetary gear had seized inside the transmission. Hopefully, that's not the case in this instance.
 

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Discussion Starter · #9 ·
Very well. Had a similar issue on the former G8. Took it to the dealership and said something going on with the transmission. Perchance being warranty work they said we can't find anything wrong with it. Few days later while driving on the freeway the car wouldn't go over forty miles per hour. Took it back to the dealership and the planetary gear had seized inside the transmission. Hopefully, that's not the case in this instance.
Well I certainly hope that doesn't happen. If it does, luckily these transmissions came in a lot of cars so I can go pull one from a junkyard.

I've been reading that BMW owners have similar problems created by a bad MAF sensor. I'm surprised to find out they also use the 5L40-E transmission.
And Saturn Sky owners have similar problems with their 5L40-E transmissions created by bad VVT Cam Actuators. I already have a set of spare Actuators.

I just wish my car would give me a check engine light to point me in the right direction.
 

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Can the code reader detect pending as well as transmission control module codes?
 

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I know the fluid level was mentioned and you said you filled it until it was running out.

To confirm: was the engine RUNNING and the trans temperature between (if memory serves) 50-60 degrees celsius? Because that is the prescribed method for checking the fluid level - running, in park, level surface, in the correct temperature range. If you filled it to trickling but with the with the engine off it would be low, and low ATF does not make for a happy tranny.
 

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I had a similar problem just before my transmission went out in my red Base. I talked with the guys at Street Smart Transmissions. They have all the up-to-date information and upgrades for the 5L-40E from all the car manufacturers that used this unit. BMW apparently did a lot of re-engineering before going to a different transmission. The three-year unlimited mileage warranty helps too. I've had mine in for three years with no complaints at all. It performs much better than when it was new. streetsmarttransmission.com
 
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