HumW166

Hi everyone,

I've gone through the W166 threads about transmission issues but couldn't find anything that matches my situation, so I'm posting here for help.

**Car Details:**
- Model: W166 ML250 Bluetec Special Edition
- Current Mileage: 145,000 miles
- Modifications: AdBlue/DPF/EGR delete and remap done in June 2023 at 139,000 miles. During the delete, a hole was drilled in the exhaust to prevent gas or dirt buildup.
- Service History: Well maintained and always serviced on time.
- Last Transmission Service: January 2022 at 119,000 miles (by SPR Autos, SK1.2JT, UK)

**Main Issue:**
- Transmission/Gearbox related problems

**Other Minor Issues:**
- Slight coolant leak

**Fault Codes:**
- None

**Description of the Issue:**
- The car jerks when shifting from park or neutral to drive or reverse while stationary.
- While driving, gears do not change properly and the car jerks and over-revs during gear changes (slipping).
- The only smooth gear shift is from 2 to 3. Possibly a downshift is smooth as well, but I'm not sure which gears. Most shifts up and down are bad.
- Because of this issue, I keep the car in manual mode to avoid sudden jerks from the 7G automatic transmission.

**Timeline of Events:**

- **March 2022:**
- Mercedes dealership performed a recall service. Reported everything as fine including a visual health check.

- **November 2022:**
- First experienced a jerk when shifting from stationary to reverse. It was intermittent, so I took no action.

- **March 2023:**
Engine cut out whilst driving.

- **April 2023:**
After weeks, still couldn't get the car to start. Finally car recovered to AMG Cheshire Specialists (SK14 4QF, UK). XENTRY test showed fuel pressure frequently lowering. This points to a high pressure fuel pump fault. May also need new Injectors. Somehow they managed to get the car started! They didn't even know how (maybe they fiddled with the electrics). Since then, car had never cut out and it's as if the issue resolved itself.

- **June 2023:**
- AdBlue delete done.

- **June 13, 2024:**
- Local mechanic replaced front CV boots and performed a full service (fuel filter, oil filter, air filters, engine oil). No fault codes were found.

- **June 15, 2023:**
- Transmission issue worsened, with jerking in every gear at any time. Initially minor and intermittent, the problem became severe.

- **July 19, 2024:**
- Local mechanic found no fault codes but mentioned a possible issue with the torque converter. There was a P0171 fault code stored (System too lean Bank 1). This came on for first time a few days ago and caused EML on dash to turn on but then disappeared the next day. Maybe this is a remininent of the fuel pump engine cut out issue I had a year ago in April 2023?

- **July 20, 2024:**
- Took the car to AMG Cheshire Specialists (SK14 4QF, UK). They found no fault codes but noticed metal in the transmission fluid, which was silvery black. They recommended replacing the gearbox, stating that a transmission service would not be effective.

**Questions:**
1. Would it be worth doing another transmission service, or will the problem likely return after a few weeks?
2. What could be causing this issue?
3. Could something in my timeline, such as a mechanic's error or the AdBlue delete, have caused this?

Thanks for reading. Any advice or input would be greatly appreciated. I bought my W166 as a keeper and haven't spared any expense on maintenance. I'm hoping to avoid replacing the entire gearbox.

Best regards,
Harry

CaliBenzDriver

Harry, I read through your precise timeline.
Your main issue is the gearbox destroying itself.
Never mind the AdBlue side tale.

This sounds like WRONG ATF WAS USED.
Normal ATF service would be in the order of 50kMi... not 10kMi to burn ATF black.

The engine Bank1 stored lean code has no relation with gearbox.

The tranny banging righ from PRND selection is significant to dissociate CAN-C networking issues.

You can easily trigger a shift relearn using 30s ON/OFF Pedal procedure shown on Youtube.

The AMG Specialist should be able to diagnose and program the tranny adaptations without charging for a £10k job.

HumW166

Retire the current transmission and replace it all?
The transmission will just eat away at itself and another oil change won't do anything good right?

They were suposedly a Mercedes specialist who serviced the gearbox on January 2022 using "Blue 4L 236.15 4 LTR" x 1.5

Transmission problems then began 9 to 10 months after that. In hindsight, I should of gone back to them instead of trusting their name.


Details

HumW166

I've understood the part on triggering a shift relearn using 30s ON/OFF Pedal procedure to combat the tranny banging from PRND issue.

What is the recommendation of action to deal with the over revving during gear changes whilst driving?

CaliBenzDriver

My "recommendation of action to deal with the over reving during gear changes" is to get tranny diagnosed before it's entirely done for.

New ATF does not seem to help prevent the oil from burning black because clutch frictions are slipping on limited pressure.

Also it may well be tranny was overheated and bad hard seals are loosing pressure then you'll need a rebuild job....

+++ plugin your favorite scanner to read ATF TEMPS

HumW166

Update as of 30/08/24:

Car started to get stuck in gears and restarting would relive that temporarily.
Then car suddenly wouldn't start.
Able to start only by directly jump starting from the main battery.
Now it won't go higher than gear 1 and changing to reverse and back causes a very hard vibration and loud sound.

Error codes also appeared for the first time:
U0101 - Lost Communication with TCM
P2759 - Torque Converter Clutch Pressure Control Solenoid Control Circuit Electrical
P0748/0778/0798/2716/2725/2734/2810 - Pressure Control Solenoid "A" to "G" Electrical

Took it to MB Specialist with Xentry said: "Gearbox Control Unit Y3/8n4 is defective"

Mechanic said needs new TCU (c.£1500)
Also may need new gearbox (c.£1100), but won't know until he opens it up.

Looking at a repair bill of c.£2600 to get it road worthy again. Thinking I will go ahead...

CaliBenzDriver

There you go... all tranny solenoids are reported failing.

Try a simple "conductor plate" then next is complete pull-out if clutches, converter and pump failed.

(Don't be surprised when repair tab easily passes the £5k mark when everything is opened up: £6.5k)

HumW166

Which parts are you referring to by "Converter" and "Pump"? What's the full name of these parts?
Torque converter and Conductor plate are part of the Gearbox which is costing £1000 fitted.

A 2012 W166 ML 250 with c.150k mileage has a market value of £7-8k.

I didn't consider if the Clutch may also have become damaged - It would be ideal if my mechanic can check if the Gearbox and clutch are faulty, before replacing the Transmission Control Unit.

Maybe I'll tell him to open it all up just to check before ordering the TCU from Germany (2 hours of labour @ £100/hour).

I'm only prepared to replace the TCU and Gearbox, as that would cost £2500. Anything more may not be worth it considering car value.

CaliBenzDriver

The ATF pump is what's located right behind the torque concerter.

I really hope your specialist can get this sorted out with "conductor plate" only. I doubt it due to clutch particulate being the source of valves contamination. The high heat cooks the seals that leak pressure necessary to clutches.

In US Dollar £2500 is less than half the cost of rebuilding, reprogramming & shifts adaptations... $6k!

Other ppl will chime in with experience... by the time you have already committed £2500, you have no other choice besides going all the way to a fully fixed warranted job.

Rebuilding tranny is a highly specialized job for EXPERTS at transmission shops.

My point here is don't get anything started unless you're committed to paying for the complete job with an honest ballpark estimate, not misleading bait-switching.
Pay if you have to get the exact complete job quote figures. It's not misterious for specialists.

I hope this repair pans out best for your vehicle.
🤞

HumW166

Just to be clear on the costs and parts:

A New TCU parts and labor costs 1,500 GBP with 12 month warranty
A Used & Fully Working Gearbox parts and labor costs 1,000 GBP (if done at same time as TCU) with 3 month warranty

A W166 gearbox already includes a Conductor Plate, Torque Converter, ATF Pump ... so I am trying to understand how my 2500 GBP cost could potentially double?

The only thing that is not part of the gearbox is the clutch, which can be ruled out not faulty pretty quick.
Also, considering the costs, rather than trying to fix the conductor plate, it's makes sense just to replace the TCU as Xentry is saying that's the fault.

Nevertheless, your comments have made me want a 2nd opinion from another transmission specialist mechanic outfit here in Manchester, UK!

trigital

1 - The TCU from the Used Gearbox is already "married" with donor car, so a pricy procedure need to be followed to re-married with your car. Also, the Torque Converter is not always included into a Used Gearbox. The Clutch is inside of Torque Convertor.

2 - My opinion is that the car was poorly diagnosticated from the beginning and the initial defective component is still present. You only "repair" the effects without troubleshoot the cause.

"AdBlue/DPF/EGR delete" I am 100% that all those was only a scam by the workshop, only to make you pay because they can not make a real diagnose - at that time the engine had just a cheap hose with a small crack.
Also, this is not legal in the UK.
3 - The workshop that change the oil when they knew about metal shavings....can be responsible for a new Gearbox as Mercedes documentation ( and the common sense..) clearly ask for a Transmission change.

The Gearbox is governed by the Engine management. The TCU just follow the maps from the engine, has no decision to take. A wrong manipulated engine SW in 99% of the cases force the multidisc clutch from the Lock-up Clutch inside the Torque Converter to become burned till the metal parts starts to flow together with the Gearbox oil.

So, in the first place because (maybe ) a cracked hose the Engine was unable to perform and the TCU responded accordingly
After "tuning" the clutch slowly burned and the Gearbox was " scratched" instead of lubricated.

In the EU, the AdBlue/DPF/EGR delete can be used as a argument for trying to recover the repair costs. Always this kind of "tuners" has just one explanation - "is not my fault, it never happens to anyone ", but if you ask him for proofs ...all clients already sold their cars.


In my opinion you will need the following:

1 - Recover and upload the original SW for Engine ECU. Repair the original motive for all this sad story. Please do not use the Adblue argument, as you delete DPF and EGR because the tuner knows about the smoke and absurd torque limitation...
Without correct SW is impossible to make a proper diagnosis, so the engine will never report the correct info/torque data, etc to the TCU, so you will never obtain a proper adaptation for the Gearbox. Without proper adaptation, disc burning can happen again.

2 - You have to clean the radiators and the pipes, as a lot of metal shavings are waiting to contaminate the "new " gearbox. Not a easy job!

3 - Install new/used Torque Converter and Gearbox only if you find a garage with proper tools and knowledge.

HumW166

To answer you points and clarify:

1. The new TCU job costs 1500 GBP and the price includes setting ("Marrying") to either current gearbox or a used replacement gearbox if needed (Replacement gearbox includes a torque converter / clutch included / ATF Pump).

2. Xentry troubleshoot of cause point to faulty TCU. All error codes point to TCU. What more are we looking for? The car was only diagnosed this weekend.

x. AdBlue delete was not a scam. It was simply to override the AdBlue system, because I didn't want to pay c.£1000 to replace a poorly designed AdBlue tank sensor only for it to fail again (the sensor is in the tank and got corroded by the ad blue, which meant my car only let me drive 800miles because it thinks there is no ad blue in the tank). Not sure what "Tuners" has anything to do with this topic - please keep your replies relevant

3. No oil was found in the ATF when it went for Transmission service in January 2022.

4. Obviously, I have found a proper Transmission specialist, and if they fit a replacement gearbox, then they will do a proper job and clean radiator pipes.

5. About the "Original Software for Engine ECU". The Transmission problem (specifically only hard shifts from PRND in Stationary) originally started 6 months before I had the AdBlue delete done. The gear jerking whilst driving started after the AdBlue delete was done.
This is an interesting point. Could an engine remap of software have caused or played a role in this issue, how can I probe this deeper as mechanics said it is nothing to do with Transmission or this issue. Do you disagree?

6. What are you referring to when you say "engine cheap hose small crack". What engine hose are you talking about that you think caused this Transmission problem?

trigital

I asked you respectfully to no use Adblue argument for deleting the DPF and EGR. Adblue system is far away from the DPF or EGR,

As I already stated, tuner delete all that because he knows that without deleting DPF and EGR the engine will melt because of his wrongdoing.

The wrong SW forced your Gearbox to die

No need to follow my opinion, although I have 26 years of experience only with MB and I saw exactly the same route like 50 times with the exact your type of car and bad choices. That's why I already know the client and tuner answers,

​​​​​​I only tried to help,


This is an interesting point. Could an engine remap of software have caused or played a role in this issue, how can I probe this deeper as mechanics said it is nothing to do with Transmission or this issue. Do you disagree?

I Already explained in detail!!.


3. No oil was found in the ATF when it went for Transmission service in January 2022.

At this point I was talking about a 3£ hose....or something not related with the Gearbox as I already explained in detail why