Step-by-Step Guide to Easily Replace TCC Solenoid Valve in the Mercedes 722.6 Automatic Transmission

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Mercedes BenzW203 Repair Manuals

Introduction

The 722.6 automatic transmission is a 5-speed automatic transmission used by Mercedes, among others in the W203 model. When the automatic transmission starts jerking, it is crucial to observe the symptoms carefully. Does the automatic transmission jerk during shifting, starting, coasting, downshifting, or only in the first gears without a gear change? The latter indicates a malfunction in the Torque Converter Lockup Clutch, abbreviated as TCC.

Das WÜK Magnetventil im 722.6 Automatikgetriebe im Mercedes W203

The TCC’s task is to minimize slip in the torque converter itself in the higher gears by locking up the converter. In this guide, I’ll outline a method for diagnosing a defect in the TCC and resolving the issue.

For every W203 enthusiast, I highly recommend the book “Mercedes C-Class W203 So wird’s gemacht.” It provides numerous guides on the most common issues with the W203.

Symptoms and Diagnosis

The TCC is electronically engaged in the higher gears unnoticed. Normally, the engagement of the torque converter lockup clutch is imperceptible. The TCC is actuated by oil pressure, triggered by an electronic solenoid.

The TCC usually operates in the following states:

  • Open: In 1st gear below 2000 RPM
  • Slip: In 2nd and 3rd gears between 1000 RPM and 2000 RPM
  • Closed: Above 2000 RPM (except 1st gear)

Common symptoms of TCC malfunction include:

  • Fluctuations in RPM between 1000 RPM and 2000 RPM
  • Jerking during acceleration in the RPM range between 1000 RPM and 2000 RPM
  • Jerk during turning or starting on an incline in the RPM range between 1000 RPM and 2000 RPM

Using a Star Diagnosis, you can temporarily deactivate the TCC. If the symptoms disappear, there is definitely a malfunction in the Torque Converter Lockup Clutch.

However, even without Star Diagnosis, if the automatic transmission jerks in the mentioned RPM ranges without a gear change, it is highly likely due to an issue with the TCC.

Defective Electronic Solenoid of the TCC

Before opting for a rebuilt transmission, there is hope that the solenoid on the electronic transmission control unit board is defective. While Star Diagnosis allows testing the solenoids for functionality, this test occurs with the engine off. Therefore, it is not possible to check a solenoid in operation.

Possible defects in the solenoid:

  • The piston is stuck or worn out.
  • The solenoid starts to flutter during operation.

Replacing the Torque Converter Lockup Clutch Solenoid

Now, I’ll show you how I replaced the solenoid for controlling the Torque Converter Lockup Clutch.

For the replacement, you will need:

The solenoid replacement takes approximately 3.5 hours. During the removal of the electronic control unit, cleanliness is crucial. Avoid placing the internals of the automatic transmission on cloths or similar materials to prevent contamination.

W203 Automatic transmission - Oil pan
A sufficiently large container should be placed directly under the drain plug to collect the automatic transmission fluid.
W203 Automatic Transmission - Oil Drain Plug
Now we open the drain plug on the oil pan, and about 2 liters of automatic transmission oil will drain out.
W203 Automatic Transmission - Disassembled Oil Pan
Now we start loosening the six screws located on the oil pan. This requires a lot of sensitivity, as there is still about 1 liter of oil in the pan.
W203 Automatic Transmission - Draining Oil
After successfully removing the oil pan, we can carefully pull out the oil filter. About 0.5 liters of automatic transmission oil will flow out again during this process.
W203 Automatic Transmission - Oil Pan, Oil Filter, and Oil Magnet
We set aside the oil pan, oil filter, and magnet to clean them thoroughly later with brake cleaner.
To remove the transmission plug, loosen the screw in the middle and simply pull it out.
To remove the transmission plug, loosen the screw in the middle and simply pull it out.
W203 Automatic Transmission Transmission Plug Socket
The transmission plug sits very tightly, as it is still held by two O-rings.
W203 Automatic Transmission Control Unit Fastenings
After successfully removing the transmission connector, we can loosen the fastenings of the transmission control unit. To do this, we need to loosen the gray screws all one turn at a time. Approximately 2 liters of transmission oil will flow out again. Remove all screws, except for two diagonally opposite screws. Now, support the transmission control unit with one hand and use the other to remove the last two screws.
W203 Automatic Transmission Entire Control Unit
After loosening the screws, we can remove the transmission control unit and remove the yellow plastic covers. Under these plastic covers are the solenoids.
W203 Automatic Transmission Solenoids
The solenoids are secured with a Torx screw and a clamp. In the picture, they are in the ordered sequence as they sit in the control unit. The solenoid for the WÜK is located in the top right.
W203 Automatic Transmission Electronic Control Board
The board can be lifted after releasing the clips for the solenoids when the two tabs are unlatched.
W203 Automatic Transmission - Screen in the Solenoid
In two of the six openings for the solenoids, small screens are located. Be careful not to lose them. If they fall out, simply insert them back into the row with the four solenoids into the two right openings.
W203 Automatic Transmission Control Unit
The transmission control unit should now be in front of you.
W203 Automatic Transmission - Entire Control Unit Cleaned
Now you should clean everything thoroughly with brake cleaner, and all openings should be well flushed. Make sure that the brake cleaner can always drain well. After the control unit has been cleaned, let it air out well and reinstall it.

Adapting/Teaching the Torque Converter Lockup Clutch

After replacing the solenoid, it is usually necessary to reset the adaptation values in the control unit. Subsequently, the torque converter lockup clutch needs to be re-adapted. Adapting the TCC can be done without a Star Diagnosis. To perform the adaptation, the engine and transmission must be cold.

  1. Start the engine.
  2. Press the brake pedal.
  3. Shift to “D” (Drive).
  4. Stand still for 15 seconds with the brake pedal depressed.
  5. Release the brake pedal.
  6. Drive until the engine temperature has risen by 10°.
  7. Stop and hold the brake for another 15 seconds with a gear engaged.

Repeat this procedure until the engine reaches its operating temperature. Then drive for an extended period at a constant speed.

Checking Automatic Transmission Fluid Level

To determine the correct fluid level for the automatic transmission, the oil temperature must be at least 80 degrees. After that, measure the oil level through the filler tube with the engine running in Park. The dipstick should be inserted until it touches the bottom of the oil pan.

Additional Links for the 722.6 Automatic Transmission

Be sure to check the following links related to the 722.6 automatic transmission:

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