E55BOF

Good morning ladies and gentlemen. Newbie here (not to MB; I've had LOTS of those...), with my first ML - a 2003 ML320 V6 with a 5G gearbox. . The car has done a genuine 49K miles, and has pretty much been standing for nine months. I've just bought it off eBay, and it turns out there's a transmission problem, which to be fair the seller may not have known about, but he's not willing to help anyway.

Not the usual thing - limp mode, or won't shift up. Mine is the opposite; it won't shift down...

Once in fifth gear, the transmission will not downshift automatically over about 40 mph even at full throttle, and the kickdown does not seem to work at all. Using the Tiptronic for manual shifts everything is normal, so I doubt it is a gearbox mechanical problem.

I'm using an iCarsoft MB II diagnostic unit.

The only TCM (Transmission Control Module) fault code the iCarsoft found was 'P2600 - Voltage Supply of Circuit 87 has Undervoltage', and that is a stored, not current, code.

Checking the TCM switches, it read: S16/5 (Transmission mode switch Implausible) and S16/6 (Kickdown Switch) Not Operating. I think the S16/5 reading is maybe a glitch, because the car doesn't have driver-switchable transmission modes (C/S/M) as all the other MBs I've had do.

I gather the kickdown switch is adjustable, so I'll try that, but I can't see how that would affect downshifts under load. Does anyone have any ideas what might be causing the problem?

khomer2

You need to first erase the saved codes and test again to see if they or any other codes come up again.
Off the top, the simple checks would be to check the switch under the throttle pedal and the kickdown solenoid valve on the tranny.
To test the solenoid valve, you need a power source so that you can at least check if the solenoid is functioning (pretty simple test to do and eliminate this as
the issue). It's possible it could be internal too in the soleniod valve itself where it's connected to the tranny.

Maj. Dundee

Have you erased all codes as khomer suggested, taken it for a short drive and checked for codes again?

Are you using the battery that was installed when this truck was sitting for 9 months?

E55BOF

Good Morning guys. Thank you for that.

I didn't think this transmission actually had a kickdown solenoid. I can't find any reference to one here: http://www.w124performance.com/docs/..._ATSG_2004.pdf.

You're not thinking of the earlier 722.3 transmission, are you?

Yes, it does have the battery it came with, but I drove it fifty miles back home, so the battery should have been fully charged. The problem was still there.

I've just been out and cleared all the codes, then gone for a drive. There are no DTCs in the TCM. I checked the kickdown switch by leaving the iCarsoft connected in datastream mode for the TCM switches, and sure enough, even with the pedal hard down, I got 'S16/6 Kickdown Switch Not Operating'. The switch clicks OK, but it isn't doing anything electrical.

I've ordered a new one. I'll fit that, then see how it goes. Fingers crossed, it will be OK. Wish me luck...

Maj. Dundee

Please UPDATE YOUR PROFILE in USER CP to include the year, model and where you live.

Then in a separate post provide your full vin #.

Maj. Dundee

Why did you order the Kick Down Sw. without knowing if you have one and not knowing its location?

E55BOF

I guess my last post was not entirely clear; I'm sorry if I confused you, but I thought it was evident from the context. I've ordered a new kickdown switch. I know that the car has one, and where it is, and and that it's not working.

A kickdown solenoid is something else.

Maj. Dundee

Please show me what a kickdown solenoid is. Provide a photo with part number.

E55BOF

I don't think I can, because I'm not convinced it exists; not for the 722.6, anyway. Better ask Khomer (post #2), and see my post #4 replying to him.

When he says solenoid, I now think he means switch. On the 722.3 this was indeed on the transmission, but on the 722.6 it is under the throttle pedal.

Agent-A01

Replace the pilot bushing(electrical connector to TCU and valve body), check for transmission oil wicking to TCU, and/or replace the conductor plate.

E55BOF

The transmission works perfectly using Tiptronic, and there are no DTCs. Maybe I should replace the known faulty kickdown switch first?

Maj. Dundee

You still have not provided your vin #. so I can check to see if you have a kick down switch.

E55BOF

Thank you for the offer, but I do indeed have a kickdown switch; it is in the carpet under the throttle pedal. I have checked, and it has not escaped...

E55BOF

New switch fitted, and working - much more positive click than the old one - but the transmission still seems to be very keen to stay in top, or fourth at best, at any motorway speed, even when I use kickdown going up a fairly steep incline. It will drop down to third fine if I use Tiptronic, so I'm assuming that MB did consider that ML buyers wouldn't be in all that much of a hurry, and it's doing what it is programmed to do. It may change as the box adapts to my driving style, but I can live with it as it is anyway.

SpenserM

Doesn't sound right still, it should down shift even if you don't engage the kick down. Some people say these year MB always seem to be in the wrong gear so maybe lol but I dont feel that way.

I would still check the connector for leaking and especially wicking as that's a common fault, gets worse over time and leads to the failure of the TCM.

Also check the transmission fluid level, it may be over filled.

And you're right it does adapt and gets more gear hold and down shift happy if you always demand a lot of torque with quick pedal presses.

E55BOF

SOLVED!

I contacted the last owner but one, who had it for three years, and he said it was a nice car, but very,very slow, and seemed to have got slower while he had it. Ah-HA! What could cause that?

We need a Lightbulb emoji...

Of all the stupid things; it was the throttle cable! The car was only getting about two-thirds throttle at most. Cable correctly adjusted, and all the lost power is back, and the gearbox changes as and when it should. Best of all, it cost me nothing but a little time.