P0730 Incorrect Gear Ratio

[rich.g.williams]

I put in a new electroplate today, all OK so far but not enough enthusiasm left over to plug the ETC computer back in and give the car a good run.

The hope is that the new electroplate will solve the problem but it just as likely may not.

Even the spurious outputs (and yes both gearbox speed sensors had similar spurious pulses) may be because the sensor is close to a transition so it flips back and forth, but then a well designed sensor would have enough hysteresis and it would not do it.

In theory it would be possible to generate two simulated speed signals to keep the ETC happy but it would create an enormous Safety concern. This gearbox can shift from 5th to 1st in two solenoid operations for a fault condition - avoiding this is probably the primary reason for the speed sensors and a primary concern for the ETC.

 

[Alex Crow]

I put in a new electroplate today, all OK so far but not enough enthusiasm left over to plug the ETC computer back in and give the car a good run.

i know the feeling. it is better to travel hopefully than to arrive, at least if you are unsure of you destination!

 

[rich.g.williams]

It is better to travel hopefully than to arrive, at least if you are unsure of you destination!

Yes exactly my feeling, this must be an old Chinese proverb!

 

[rich.g.williams]

cleared the error codes reconnected the ETC and went for a drive

1st to 2nd, 2nd to 3rd and straight into Limp Mode

What's left to do now?

electronic selector lever?
ETC computer?
adaptations?
differential ratio?
CAN bus data (road speed, torque, etc)

 

[Alex Crow]

sorry rich, that IS bad news. all i can say is it's not the rpm sensors .

yes, get the info from the diff and we'll check that. also, get plugged in to a star machine, but not mine , i like challenges yes, but within reason!

 

[rich.g.williams]

not to worry - its the journey, whatever one encounters along the way, the journey continues

there was a little bit more of that fine aluminium flake in the sump pan this time too

am taking it to a reasonably local indie early next week for their opinion and STAR reading

its strange the ETC decides soon and so easily to go into limp mode and yet the gearbox can change gears really really hard if working pressure is full on

 

[kebo57]

Hi I've read this thread and you've left me for dead, but its is very interesting it's a bit difficult for me to add to your diagnosis,
But I had a wing mirror changed on my ML with Sean guy at Read & he Leant me a MB car for a couple of hours and that want in to limp mode so I stopped and phoned him he said no problem it was because the car had stood & battery was down & I should re-start & it would be OK but it never did came out of limp mode.
I drove round in limp for 2 hrs I took it back still in limp mode he just laughed said don't worry it will be fine.
I know you lads will probably know about the voltage but that's all I can add

Kevin

 

[rich.g.williams]

kevin,

thanks for your genuine concern - the battery is oversize for the car and one thing the car does is start like a rocket no problem, that said I do notice the charging voltage seems quite high, I've measured it up at 14.38V then it drops off a bit

 

[rich.g.williams]

alex, television,

well i took the car to an indy some 40 miles away last december and it was booked in to have a new transmission fitted in january 2010

weeks and weeks went by, they fitted recon transmission - still going into limp mode

more weeks second recon transmission fitted - still going into 3rd gear limp mode

after trying several possibilities indy finally decided to fit recon differential

when the recon differential arrived it would not fit

called in to indy last week they found that whole differential/rear sub frame fitted to my car was probably from a C180 petrol not C200 diesel as it should be

so new transmission now new rear sub frame still no guarantee car will ever leave 3rd gear limp home mode, car still with indy

bought the car from M65 Car Sales, Darwen, Blackburn just under one year ago, they had subcontracted preparation of the car to Mercsmart also of Darwen Blackburn.

seems i got taken for a ride!

 

[Alex Crow]

that is a shame rich, we did speak of the diff ratio way back, and it is easy to read off the casing...

 

[rich.g.williams]

yes and ironic because i tried to read the differential part number myself, couldn't find the right part number (no pit or ramp), then started to look at all the C-Class differential ratios and decided they were all the same anyway

what i never dreamt (and neither it seems did the indy who has the car now) was that some wally had replaced the entire rear sub-frame with a C-Class C180 Petrol not C200 Diesel

ironic also that this car never made it out of 3rd gear limp home mode since a CAT D shunt in 2005 despite having two previous owners, two previous MOT's and being sold to me by M65 Car Sales in Darwen Blackburn

nothing i can do about it because the car could pass an MOT without being declared unroadworthy

 

[peet606]

Hello Rich,

Thank you for sharing the useful information.

I am facing this problem too. I took an OM606.962 from w210 and put into w461. The car had 5 gears in first 20 mins and stayed at 3rd gear later on. I had to shift to P or restart the engine to get all 5 gears. And after a while, the problem repeats.

How did you solve on your car? Can you share?

Thank you,