722.6 gearbox occasionally sticking in 3rd. Conductor plate or speed sensor next?

[bully]

I have a SL350 (R230) 2006 with a 5 speed 722.6 box that's occasional sticking in 3rd when warm in Sports mode but not when in Comfort mode. No engine management lights coming on. Getting a OBD-11 code 715 defined as 'input/turbine speed sensor circuit A malfunction' but if it were a speed sensor issue I would have thought both modes would have been affected? Also, when it gets stuck in 3rd in Sports Mode I can't change the selector from 'Sport' to 'Comfort' until I stop the engine and restart. The sticking issue then disappears for a while too. Gearbox smooth with no jerkiness. I've had the adapter for the 13 pin plug changed but no improvement. Had a transmission oil change recently as well but this started before that. Should I change the speed sensor and lead next (I think it sits on top of the flywheel bell housing) or bite the bullet and get the conductor plate changed?

 

[LostKiwi]

The speed sensor is in the gearbox on the conductor plate. The one in the bell housing is the crank position sensor.

On the conductor plate there are two speed sensors. One measures input shaft rotational speed and the other output shaft rotational speed.

 

[bully]

Thanks for that. Do my gearbox issues sound like the conductor plate is going for a burton? Does a new one need coding to work with the car?

 

[malcolm210]

Yes mine went the same way on a 210 stuck in third as soon as the gearbox was really warm say 20mins driving, reset cured everything for a couple of weeks then the transmission stuck in second permanently new electric/conductor plate cured the issue but there are specific codes so might be worth a session on STAR to confirm

 

[LostKiwi]

Thanks for that. Do my gearbox issues sound like the conductor plate is going for a burton? Does a new one need coding to work with the car?

Yes it does need replacing.
Pretty sure they don't need coding but will probably need adaptations resetting.

 

[alexanderfoti]

Yes, sounds like conductor plate, no coding required. Adaptions resetting would help, but it will drive without.

Conductor plate is on top of the valve body. oil out, sump off, filter off, electroplate off, swap plates, reverse order. Messy job but not complex.

 

[bully]

Thanks guys. A STAR gearbox adaptations reset takes wear and tear in the gearbox into account but with only 51k on the clock I wonder how much extra it would add apart from cost? I've done a TCU reset before using the MercMedic process which I could do again if the beastie is a bit uncertain after a conductor plate change maybe that will do the trick?