Gearbox having a brain fart

[Nunners]

Hey there I’m new here. I’ve got - c320 2009 auto with 66k on the clock.

every now and then my gearbox will have a brain fart. After a decent drive about an hour or so when been driving on a motorway and then come to a stop for a round about or something. The gearbox won’t shift down and if I try to manually shift it will go down but won’t have much power.
I’ve just got an gearbox service as I was told that may be the issue. Just taken it out today and it was playing up again.

has anyone else had this issue or know what it could be?

thanks

 

[whitenemesis]

Don't guess get the codes read using STAR.

 

[mercmancdi]

Hey there I’m new here. I’ve got - c320 2009 auto with 66k on the clock.

every now and then my gearbox will have a brain fart. After a decent drive about an hour or so when been driving on a motorway and then come to a stop for a round about or something. The gearbox won’t shift down and if I try to manually shift it will go down but won’t have much power.
I’ve just got an gearbox service as I was told that may be the issue. Just taken it out today and it was playing up again.

has anyone else had this issue or know what it could be?

thanks

Did you make sure that they did a transmission fluid flush as it can make a good difference between that and a simple fluid change.
And at the price of fluid it makes a big difference to the cost if it was done cheap then I suspect it was not flushed. I m o

 

[Jobsworth]

I’ll bet you have a speed sensor fault logged in the transmission ecu

 

[markjay]

Did you make sure that they did a transmission fluid flush as it can make a good difference between that and a simple fluid change.
And at the price of fluid it makes a big difference to the cost if it was done cheap then I suspect it was not flushed. I m o

The 7g is due an ATF and filter change every 3 years.

 

[Nunners]

Did you make sure that they did a transmission fluid flush as it can make a good difference between that and a simple fluid change.
And at the price of fluid it makes a big difference to the cost if it was done cheap then I suspect it was not flushed. I m o

I believe they did a flush when they changed it.

I’ll bet you have a speed sensor fault logged in the transmission ecu

Would this come up using a scanner?

The 7g is due an ATF and filter change every 3 years.

I got the car just under 3 years ago at 40k and I know the gearbox was serviced before I got it

 

[Petrol Pete]

Hello and welcome. We need a little more information regarding the 'fault' and EXACTLY what was done (or not done) to sort it out. Don't panic Nunners, I doubt that your problem is not anything we have not dealt with before.

Hang in there for good advice from many on here

 

[Nunners]

Hello and welcome. We need a little more information regarding the 'fault' and EXACTLY what was done (or not done) to sort it out. Don't panic Nunners, I doubt that your problem is not anything we have not dealt with before.

Hang in there for good advice from many on here

Thanks for the welcome.

so when driving on a motorway for a long period of time an hour or so everything is fine but when I come to a stop in traffic or coming off at a junction the car won’t shift down by itself and the only way to get it to shift down is by doing it manually.
If I turn the car off and back on the issue will disappear for a little while.

I have a cheaper ob2 reader and nothing shows up. No lights on the dash come up either.

 

[Joesoap17]

you could possibly have a conductor or connector sleeve plate issue but without codes from a good scanner or a Star scanner you ar peeing in the wind.

 

[louwdj]

How sad that posters do not return with feedback on their outcomes.

 

[mioba]

@Nunners

What was the solution in the end....

 

[zipdip]

Yes I agree with posters not coming back with the solution,with these gearboxes,you do need to change the ATF every three years,but if you get a problem like the one in this post,they all tend to be roughly the same at some point in the drive you will encounter the auto box not doing what it is supposed to,in my case it was the same bit of road,and so you stop the car switch off wait 10 mins and start it up and all is well until the next time,you then have to make a decision ,have the car put on Star at a cost to see if there is any fault recorded,now sometimes there are no fault codes,the next decision is do you do a ATF change,and hope that cures it,if it does not then the electroplate will have to be serviced by a specialist like valvebodies ,for my money when the box plays up it is best to go the valvebodies route straight away,cost about £600 with new ATF,against say £300 for a ATF change that may not work,and of course is wasted when you have the electroplate repaired.