I took my MINI to a tranny shop the other day cause it shifted a little slower and sharper. They said the problem was the voltage was low and they told me to check my battery/alternator. So I had the battery, alternator, and starter checked and the voltage was all good for these.

I need your insight on this. Have you experienced anything like this? If the voltage is indeed low, what would the cause be if not the battery or alternator?

 

the codes could be past codes from when the batter was indeed low and/or replaced. Clear codes and see what pops up. On the other hand, depending on the mileage, you might had burned ATF and due for change. Also, it is a possible the valve body is getting clogged or solenoids sticking/gunking up. Unscrew the ATF drain plug just to get few drops for color/smell inspection.

 

A low battery or or more likely insufficient output from the alternator can cause all sorts of issues from spurious and not so spurious warnings/error messages to engine even transmission issues. Generally if the voltage drops this low there should be an error code logged though it might be a BMW proprietary one.

Also, keep in mind while the alternator can appear healthy right after engine start with another car I have seen the alternator output drop over a 15 to 30 minute span of time. The battery voltage falls from around nearly 14V to around 12V. Had I continued to drive the car chances are all sorts of things would have happened.

I knew this was not unusual as some time before at the dealer I watched another car in the service bay with a failing alternator. The tech started the engine and the engine fired right up and ran ok. But after a few minutes some warning lights appeared, the engine starting running rough, the CEL came on then shortly thereafter the engine died. The tech turned off the ignition and repeated this around 15 minutes later and all was well. For a brief time then it all went downhill again.

 

I had my mechanic drop the pan and replace all the fluid 3.5 years/24k miles ago. The tranny guy I took the car to said the ATF looked good.

But it just seems there is a slight delay in shifting a few times here and there (no slipping).

Any recommendations for next steps? How would I check the valve body or solenoids?

 

Lookup 09G transmission on youtube. Our transmission mission is also used on VWs. You can ohm the solenoids and/or take the valve body and clean it up.