722.6 kickdown problem 1996 SL600

[Hereward]

I have a late 1996 R129 SL600.

Recently the use of kickdown has resulted in the immediate trigger of Limp Mode and illumination of the BAS/ESP orange light. Restarting the engine clears the symptoms until kickdown is tried again.

If kickdown is not used the car drives perfectly, with no issues whatsoever. It will cycle up and down through the gears with no problems at all. It is solely attempted kickdown that immediately triggers the problem.

I have Carsoft diagnostics and the following codes are present (code descriptions take from Actron.com):
P0150 - O2 sensor circuit malfunction
P0818 - Driveline disconnect switch circuit
P0006 - Fuel shutoff Valve A control circuit
P042A - Cat temp sensor circuit
P007B - Charge air cooler temp sensor circuit (BUT CAR IS NOT TURBOCHARGED!)
P2801 - transmission range sensor B circuit

Other info:
- The two O2 sensors are brand new. They were the first thing I replaced.
- The ATF level is correct
- The pilot bush is dry and corrosion free

Grateful for any advice. On typing this up I notice the word "circuit" is present in every error code description - is the conductor plate worth looking at? Also, the battery seems fine and is always on a CTEK charger when not used but maybe worth bunging in a new battery?

Thanks.

 

[Petrol Pete]

I have a late 1996 R129 SL600.

Recently the use of kickdown has resulted in the immediate trigger of Limp Mode and illumination of the BAS/ESP orange light. Restarting the engine clears the symptoms until kickdown is tried again.

If kickdown is not used the car drives perfectly, with no issues whatsoever. It will cycle up and down through the gears with no problems at all. It is solely attempted kickdown that immediately triggers the problem.

I have Carsoft diagnostics and the following codes are present (code descriptions take from Actron.com):
P0150 - O2 sensor circuit malfunction
P0818 - Driveline disconnect switch circuit
P0006 - Fuel shutoff Valve A control circuit
P042A - Cat temp sensor circuit
P007B - Charge air cooler temp sensor circuit (BUT CAR IS NOT TURBOCHARGED!)
P2801 - transmission range sensor B circuit

Other info:
- The two O2 sensors are brand new. They were the first thing I replaced.
- The ATF level is correct
- The pilot bush is dry and corrosion free

Grateful for any advice. On typing this up I notice the word "circuit" is present in every error code description - is the conductor plate worth looking at? Also, the battery seems fine and is always on a CTEK charger when not used but maybe worth bunging in a new battery?

Thanks.

Have you tried to 're set' the gearbox yourself by having the ignition on and burying the accelerator pedal into the carpet for 30 seconds etc..?
I can't remember the full re set procedure off the top of my (bald) head , but its out there on MBmedic website . No doubt someone on this forum will know of it, and indeed if its worth trying or best avoided.

Good luck

 

[Hereward]

Problem solved.

I fitted a new conductor plate. Some moron had been in there a few years previously and over-torqued all the valve body T30 bolts. I had to Dremel the head off one of them after rounding it off and luckily the threaded section could be unwound with pliers. Not a pleasant experience.

The conductor plate I replaced was made in 2012, so not very old at all. It could be that there was nothing wrong with the plate and simply re-seating the solenoids on the new plate sorted the problem. I also fitted a new section of intake hose between the left MAF and the throttle body (to replace a cracked section) so that could also have sorted the issue (by tidying up the fuel/air mix). Anyway, I will never know. Problem solved and the car is happy to kickdown again.