Hi Guys,

My transmission had occasionally clunked from P to D recently, but then last week I started off driving in 1st and is stuck there. The check engine light is also on. I tried manually shifting but nothing will get it to upshift. It does go into reverse OK however.

I took it to a local mechanic a couple of blocks from my house and he put the analyzer on it and it gave the following codes; P0715 Input turbine speed sensor and P0720 Output shaft speed.

The mechanic didn't go any further but it said it would be about $2500 to fix and he would have to open it up to give me more detail, but it wouldn't be over that.

Any ideas what I'm looking at here? Would appreciate any advice (other than take to the MB service center- which I realize I will probably have to do).

Thanks, Rich

first,and see if that helps the problem.If you are a diy person you can do the job yourself.
Those speed sensors are on the upper part of the valve body,no way it is a $2500 job.The trans does not have to be pulled,the pan needs to be dropped the valve body removed and the new sensor assembly installed.Parts,gaskets and fluid at the dealer about 800 bucks and then labor added to that.One case where the dealer may be your best bet or find a good indie mercedes shop and have them quote the job.Run from the guy down the block,he is a rip off!
Some of those sensors are optical and when the fluid gets dark they fail to send the correct output to the trans computer(tcu)
ohlord
"GOT CODES?"
The earlier trans may even have external access to those sensors so call the dealer and find out where they are mounted on your 420 model.Might be a lot less if they are the kind that plug in from the side of the trans.Cross your fingers.

Hi Ohlord,

Thanks for the response. I'll try the fluid change first. Fingers crossed.

Rich

that happened to my car too, and for some reason the car went into limp mode, so the mechanic reset the TCU and the car has been fine since

mine is stuck in second..... I have had rear end trans issues with this car ever since eibach had their kits numbered incorrectly and I have had springs in the rear for the auto leveling car..... I am going to try and reset the trans computer and have the actuators tested because i aint into dumping 2k into this car right now

In lymp mode and need help..... had a guy look at it and he says new tranny.... I say sockit buddy...... Also my cruise control doesn't work.... dude says i need a new tranny, but i think he is full of malarky.... any help is much appreciated..... Thank you.....

This happened to my car. It's the limp-home mode. My mechanic first tried tranny fluid, filters, and installing the later generation metal magnet for $380. Worked like a charm for about 2 days - when viola - the car went into limp mode again. The car had to go back and they changed the valve body. The job was about $1,200 and to top things off - I had to change the tranny fluid and screens and magnet again.

I think I have the cleanest transmission fluid in the country.

Just bite the bullet - save yourself some time and agrovation - do the valve body. While the car is apart they can check the gearset to make sure all is well.

Also, make sure you go to someone that has had some experience with doing these.

I have a vague recollection that there is a spring the tensions one of the sliding valves that breaks and then threads into itself, rendering that valve inoperable.

As indicated above, make sure whoever works on the transmission really knows what they are doing.

Also, did whoever did the diagnostics check for codes? Problems with the optical sensors in the tranny should throw codes...

Keep us posted.

JR

Well, of course anything can happen. But like Ohlord said, itīs the electrics kit above the valve body that fails most of the time and usually not the valve body itself.
There is also a small control unit located under the gearshift lever, which sometimes fails. When that happens, your car will get stuck in 1st gear when cold. Then after a short time everything will get back to normal.

Cheers,

My car gets stuck in first sometimes, somedays it does and somedays it doesn't. 95% of the time it happens when I am first driving the car and it has not yet reached operating temp. Other than that the transmission shifts very smooth. Check engine comes on and goes off after a day or so of that happening.

Is this issue the valve body? or will itmost like be a fluid change and the sensors?

Like I said..
I believe that the control unit under the gearshift lever is your culprit..

Cheers,

he is showing a input /output sensor failure,that is the most probable culprit,and a not totally uncommon failure with these transmissions.

Ohlord, wonīt you buy me..
-Drink up mate..

Cheers,

clear the codes and disconnect the battery and step on the brakes for 30 seconds and rehook up the battery on the chance that it could reset the trans shift module referred to by our old school expert.That way you have ruled it out or in depending on the results

this happened to me like 6-8 months ago was your temp gauge pegged??
cose me about 1800 bucks in repairs.

I had limp mode problem also and p0720 code but was intermittent. It would reset if I turned the key off and restart. Then would be fine untill next day. Car started easily everysay but believe it or not the battery was bad. The amps were good enough to start but the voltage level was too low. I changed the battery and haven't had the problem for 2 months now. I got lucky i guess. A battery is a lot less than having transmission work done especially if you haven't replaced it in a while and are due. thought it was worth mentiois.ning th

same thing happened to my car i took it to mechanic and it was conductor plate cost me about $700 to fix it.

Is replacing the control unit a do it yourself item? If so what is the approximate cost of the unit?

What are your symptoms?do not be worrying about conductor plates and such without checking several other items.are you stuck in limp mode?have you checked the electrical plug at the transmission for the common leak that causes limp mode shift problems?have you spilled liquid on the shift console by mistake?If you are not an accomplished diy'r at least find a shop with sds diagnostics and have them ran for codes and the above mentioned connector inspected for leaks.
keep us posted.

My symptoms were last winter and have not occurred all summer but I have no doubt it will occur again when the weather gets colder. My '99 wagon sits out all night and in the winter it stays in first gear and I have to pull over and wait a few minutes and then it is OK. Trans. was rebuilt at 80,000 miles at a cost of $2000 at an independent shop and a year later it developed this problem and the same shop changed the fluid and said nothing to worry about because this what Mercedes do. I now have 135,000 miles and I believe there is a correction available as mentioned in an earlier post. I have not spilled anything on the console and I don't know what "safe mode" is and the check engine light has never come on. Any guesses?

Had this same problem a while ago, cost me about 800 i parts and labor, + fluid.

is a protection feature.The trans slip into a mode of 2nd gear and reverse only.Have someone or yourself check the electrical connector on the passenger side of the transmission.On a lift or on ramps but be safe.Leaking connector needs to be removed cleaned out and installed with the upgraded kit.20 bucks or so for parts.Diy on benzworld.org w210 section or search
leak 722.6 transmission
on everythingbenz.com
one of the forum members put together this Mercedes search engine.

Not sure about the cost of this item in your area, but I seem to remember it was around 150 - 200 Euros.
Itīs hardly a DIY to replace it if you are a newcomer to such things.. You must remove the complete center console and the air vents to remove the shifter. Then you must disassemble the shifter unit altogheter, which requires a bit of patience and care. It can be a bit tricky, but nothing severe..
Close to 3 or 4 hour job, if I remember correctly.
-Cheers.

not asking about the shift module,he was asking about the valve body control unit.Sits on top of the valve body inside the transmission,if bad you need to dump the fluid,remove the trans pan and the valve body making sure no dust or dirt gets in there and replace the electrical plate on top of the valve body.It can be done by a diy'r.But start with the most common suspect,the leaking part mentioned above.If it leaks it can cause all kind of fits

Many thanks to ohlord and 124-Fan for your quick responses, I will check for a leaking elect. connection first chance that I get and hope for the best.