MERCEDES W203 FACELIFT: GEARBOX ISSUE, DRIVE IN LIMP MODE. NOT ABLE TO SHIFT TO REVERSE OR PARKING

Transmission Issue: Unable to Detect Gear Location

Fig 1: Symptom of Gear status unknown

Symptoms:

• Gear status unknown (as in the picture above: Fig 1)
• When attempting to reset, the car can move, but in "Drive" mode, it only operates in limp mode.
• Unable to shift gears to "Reverse" (R) or "Park" (P), only to "Neutral" (N).

Observed Behavior:

• Limp mode activated.
• Gear status not detected.
• In "Drive" (D) mode, the car moves but only in limp mode.
• Gear cannot be shifted to "Reverse" or "Park."

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Troubleshooting and Rectification Steps

Initial Steps:

1. Perform a gearbox reset. If the problem persists, proceed to the next steps.
2. Verify the last gearbox service. If it is still within the recommended service interval, follow these solutions:

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Solution 1: TCU Check and Cleaning

• Remove the Transmission Control Unit (TCU) and inspect it.
• Heat the TCU board (the electrical board inside Fig 2) in an oven at 200°C for 6-8 minutes to reflow the soldering.
• Reinstall the TCU and test.
• If the problem persists, proceed to the next step.

Fig 2: TCU body (inside is the control circuit)

Fig 3: TCU location on passenger side

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Solution 2: Gear Shift Selector Inspection

• Remove and inspect the gear shift selector in the centre console (Fig 4).
• If needed, heat the selector board (Fig 5) in an oven at 200°C for 8 minutes to reflow the soldering.
• Reinstall and test.
• If the issue is resolved after reheating, the selector is likely the cause.
• If the problem remains, proceed to Solution 3.

Fig 4: Gear shift selector on the center console

Fig 5: Board inside gear shift selector

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Solution 3: Gearbox Components
If the issue persists, it may be a more significant problem with the gearbox. Troubleshoot in the following order:

1. Conductor Plate:

• Replace the conductor plate, ideally with the solenoid included, as this component may be causing incorrect gear signal transmission. (Fig 6)

2. Valve Solenoid:

   • If replacing the conductor plate does not solve the issue, replace the valve solenoid.

3. Professional Consultation:

   • If none of the above solutions work, the problem may require dismantling the gearbox. Seek professional assistance.
     
     
     
     

     

     Fig 6: Conductor plate
     
     
     

Fig 7: Valve and solenoid with conductor plate

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