[SlimE92]

What's up guys. Just yesterday I noticed the car downshifting roughly when coming to a stop at a red light from 2nd to 1st (at tranny), but now when I put the car into reverse to back up the car will begin to reverse but if I let go of the gas and let it hang I'm reverse for a second it feels like if the car slips out of the gear and the car won't reverse no matter how much gas I give it it'll just rev up and then I get a transmission malfunction reduced acceleration on the idrive screen and a cog wheel symbol on the dash as well as no reverse. When I try to shift into reverse it just stays on neutral. But when I turn the car on and off reverse will work again with the same symptoms if I let it hang it'll slip out the gear. I read the codes with bmwhat and pulled up this A0B1 fualt code. I couldn't find to much info about it and will be taking the car to my Indy on Friday. Anybody have any ideas?

[SlimE92]

Nobody?? I've been hearing about a mechatronics sleeve?

[BMWCOUPE]

Could be as bad as needing a new transmission or an electronics sensor issue. Do you hear a loud "thunk" noise when you are putting it in reverse?

[SlimE92]

Originally Posted by BMWCOUPE

Could be as bad as needing a new transmission or an electronics sensor issue. Do you hear a loud "thunk" noise when you are putting it in reverse?

I hope it's just a sensor as my car is a 08 with only 72k on it. No thump or noises or anything and it seems to be random. Just now I reversed perfectly fine, but other times it'll just be reversing n then just stop all of a sudden but I don't feel any clunk or thump sound when it does do it

[shadow191]

Sounds like some sort of valve body issue. If there is an issue with the solenoids or signals driving them, it could cause the reverse issue. All the shifting in autos is done by the solenoids so if one fails the car may not shift correctly. There are usually solenoids that shift car from park to drive, park to reverse, and the gears themselves.

I googled the A0B1 code and it looks like the transmission can't recognize what position the shifter is in. The shift lever does actually move a piece in the valve body to indicate position. So it could be that the sensor is damaged and sending the wrong signal. Or the part itself is damaged, but that's less likely since it resets after you shut the car off. I'm guessing the indy shop will find a problem in the valve body. Good news is, the rest of your transmission is probably fine.

On another car, I had similar issues with shifting. Had a modified valve body in it and one day the car stopped shifting while idling at a light. Would only go into 4th gear since it was in limp. When I turned the car off and restarted, it would go away. But if I stopped at a light too long, it would trigger the limp as soon as I stepped on the gas and lock into 4th. If I didn't stop, it would shift fine. Turns out, it was the solenoid that switched the car from neutral to in gear. I'm guessing that your issue will be similar, but with the sensor and solenoid that goes from park to reverse. I swapped back to OEM valve body and problem solved, no other transmission damage.

[SlimE92]

Originally Posted by shadow191

Sounds like some sort of valve body issue. If there is an issue with the solenoids or signals driving them, it could cause the reverse issue. All the shifting in autos is done by the solenoids so if one fails the car may not shift correctly. There are usually solenoids that shift car from park to drive, park to reverse, and the gears themselves.

I googled the A0B1 code and it looks like the transmission can't recognize what position the shifter is in. The shift lever does actually move a piece in the valve body to indicate position. So it could be that the sensor is damaged and sending the wrong signal. Or the part itself is damaged, but that's less likely since it resets after you shut the car off. I'm guessing the indy shop will find a problem in the valve body. Good news is, the rest of your transmission is probably fine.

On another car, I had similar issues with shifting. Had a modified valve body in it and one day the car stopped shifting while idling at a light. Would only go into 4th gear since it was in limp. When I turned the car off and restarted, it would go away. But if I stopped at a light too long, it would trigger the limp as soon as I stepped on the gas and lock into 4th. If I didn't stop, it would shift fine. Turns out, it was the solenoid that switched the car from neutral to in gear. I'm guessing that your issue will be similar, but with the sensor and solenoid that goes from park to reverse.

Man I hope so, I'm going in tom afternoon to my Indy to see what they say it is for sure, hopefully it's just one of the solenoids. Thanks for the info. I just noticed this morning after an engine oil level low light that there is a leak of oil in my engine bay all over. It seems that it's coming from the oil filter housing so I'm hoping it's the gasket I doubt that's causing the tranny issue just another problem in itself. Man if I didn't know what I was getting myself into before I bought the car I would be so mad lol

[John 070]

it's not simple, but I think it's possible to drive a car that can only go forward. Just need to keep it head out. If parallel parking in the city, may have to wait once in a while because you can only park head in in limited situations.