Automatic stuck in third

[Crustyoldbloke]

Hi Everyone

Just returned from a week away where my autobox got stuck in 3rd 4 times. I suspect a sensor as being the cause since switching off and restarting the car cured the problem each time.

Whilst I was stuck in third, I was unable to select S from C, and unable to manually change up or down a gear with lateral movement of the gear selector.

Has anyone else experienced this? If so, what was the cure?

 

[whitenemesis]

Sounds very much like the speed sensor on the electro-plate is failing, not uncommon. Get the codes read firstly, then probably a new plate needed. Around the £600 mark including ATF and fitting.

 

[Crustyoldbloke]

Thanks Whitenemesis, that certainly sounds feasible. I did ask my indy to change the ATF, but he said he couldn't due to the reserve chamber and that they were sealed for life after the first service anyway, but to me, 88000 miles needs fresh fluid.

With this current problem, I noticed that engaging reverse was quite fierce also (quite a powerful clunk) as was subsequently engaging drive.

 

[BlackC55]

It will be a speed sensor issue probably. Get eh codes read.

A new electrical plate is the usual repair method. You will need either a dealer to do it or someone with an official Star.

 

[Crustyoldbloke]

Thanks BlackC55. Are eh codes the ones you get from the OBD? Since returning from my Devon mini-break, the car has been 100%, so now I'm wondering if it might just be wanting fresh ATF. I have decided that I am going to keep this car for a few more years as I just like it so much and it hasn't cost me much in the 3 years I've had it.

 

[zipdip]

Well you need to get any codes,the problem is that sometimes none are stored when the gearbox plays up,I take it you switched the car off removed the key and waited for a few minutes and then you could drive normally,it may well be electro-plate ,if you buy a new one then it will need to have it coded to your car with star if you get it repaired then it can go straight back in and it will hopefully work,it is one of the major things that goes wrong with the 7g box but at least it has become cheaper to fix around £500.

 

[Crustyoldbloke]

Thanks zipdip, you are correct in that I did pull over, switch off the ignition for a few seconds, restarted and all was well. It certainly sounds like an elctro-plate problem from what I have gleaned so far (I am not a mechanic), however I am not going to dismiss the idea that it may just be an ATF problem, caused by the lack of viscosity or volume, producing a fault when hot. My debit card is ready for a hit!

 

[zipdip]

Of course try the ATF oil change,it is a service on the gearbox,that includes filter, gasket and new sump bolts as they are white metal and are only used once,so as always you take the chance that if it does not cure the problem then you have added the service to the electro-plate repair best of luck.

 

[Auto-mobile]

Bolts are reusable on 722.6.

Your Indy said said he can't service it because it's sealed for life?

 

[redjules51]

Had the identical problem about 4 years ago. Speed sensor. My Indi charged around £380 inc ATF but I do have 5 speed and not 7.

 

[zipdip]

Of course it is a 5g forgot that model had that box until 2009

 

[Crustyoldbloke]

Yes it is the 5-speed 722.6. My indy couldn't/wouldn't complete the ATF change as he could not drain the ATF reservoir for whatever reason (lack of necessary tools or didn't want to do the job). He said that the gearbox also had a reservoir which would remain full if he just allowed the ATF fluid to drain, so just replacing the fluid lost would not renew ALL of the ATF. He told me not to worry about it as MB claim that they are sealed for life after the first service. As he is now retiring, I have to look elsewhere for a new mechanic; maybe one with more enthusiasm.

My understanding now is that an ATF change might be an added expense if I find that the problem still exists and I have to go for an electro-plate change, so maybe I just bite the bullet and have electro-plate and ATF change at the same time. I am dreading using an MB main dealer for this as they charge about £160 + VAT an hour, but if the coding can only be done by them, then I have no choice.

 

[whitenemesis]

You have Jay from Mecland not that far from you ...

 

[BlackC55]

It doesnt have to be main dealer just someone with an official star machine. We are in Horndean, Hampshire and could certainly help with this if you are close.

 

[Crustyoldbloke]

Thanks, but I hope I can find someone a bit closer than the 45 miles to Nuneaton or 140 to Horndean. Since being back from hilly Devon, the problem has not arisen; I don't know if the error codes will be recorded, but all the very good advice I'm getting from people with more knowledge than me, is to go for the electro-plate replacement, which makes sense as I am going to keep this car for a few more years yet. I am extremely grateful for all the contributors to this thread.

 

[Codger49]

Many independent Mercedes specialists will have the online connection to Mercedes, certainly those often mentioned in this forum do. I would expect MSL in Birmingham have it as well as Mercland. If you do get your electroplate replaced, ask for the gearbox software to be updated as well, it made a noticeable improvement to changes in my 2006 7G box when I had mine done.

Just ask them if they can do SCN coding.

 

[Crustyoldbloke]

Thanks for that advice Codger49, I will certainly ask about that being available for the 5-speed box. Once every couple of months I reset the gearbox as per the instructions on YouTube, and it always makes a big difference anyway. I dislike the Sport settings; far too edgy for me, but there is a noticeable difference in Comfort setting too.

 

[freshprince]

Hi Everyone

Just returned from a week away where my autobox got stuck in 3rd 4 times. I suspect a sensor as being the cause since switching off and restarting the car cured the problem each time.

Whilst I was stuck in third, I was unable to select S from C, and unable to manually change up or down a gear with lateral movement of the gear selector.

Has anyone else experienced this? If so, what was the cure?

got the exact same problem at the moment had it code read not with star saying gear stick but seems according to people on here electro plate

 

[Crustyoldbloke]

I took mine to a "Merc specialist" (without STAR) on 20 March, only for them to run a diagnostic check and tell me that they wanted to keep my car for two weeks to sort it out. I have been in touch with a Merc specialist with STAR and they want the car for three days to replace the electric plate for £534.48 inc VAT.

 

[freshprince]

I took mine to a "Merc specialist" (without STAR) on 20 March, only for them to run a diagnostic check and tell me that they wanted to keep my car for two weeks to sort it out. I have been in touch with a Merc specialist with STAR and they want the car for three days to replace the electric plate for £534.48 inc VAT.

where abouts is the garage or do you have a number