Transmission Range Sensor

Replace the transmission range sensor (also called transmission position sensor or PRNDL sensor) on the 9G-TRONIC automatic transmission. This sensor communicates gear selector position to the TCU and instrument cluster.

Warnings

Tools required

Parts

• Transmission range sensor × 1 — A0005406217 or A0005407017 (verify for 9G-TRONIC 9G590)
• Transmission range sensor seal/O-ring × 1 — Use OEM specification

Fluids

• MB 236.17 ATF — 1 qt

Preparation

1. Park vehicle on level surface and engage parking brake.
2. Allow transmission to cool to ambient temperature if recently driven (transmission fluid is extremely hot after operation).
3. Disconnect negative battery terminal and wait 5 minutes for system capacitors to discharge.
4. Raise vehicle on lift or secure on jack stands with all four wheels off ground for access underneath.
5. Remove engine undertray panels using Torx fasteners (typically T25 or T30) to access transmission from below.

Procedure

1. 1

   Locate the transmission range sensor
   From underneath the vehicle, verify the exact location and mounting of the range/selector position sensing for the 725.0 9G-TRONIC before proceeding — on this transmission the gear position is typically sensed by the internal VGS/mechatronic controller within the valve body rather than by a discrete externally bolted sensor. Confirm with Mercedes-Benz service documentation (WIS) whether a separately serviceable external range sensor exists on this unit, its side of the case, mounting fastener count, and connector type.
2. 2

   Position drain pan and disconnect electrical connector
   Position a drain pan beneath the work area. Fluid loss will depend on the actual sensor design and location; verify expected ATF loss against Mercedes-Benz documentation once the correct component and its mounting are confirmed. Press the locking tab on the electrical connector and disconnect it from the transmission range sensor. Secure the connector away from the work area to prevent ATF contamination.
3. 3

   Remove transmission range sensor mounting bolts
   Remove the mounting bolts securing the transmission range sensor to the transmission case, verifying the exact count and fastener drive type (E-Torx vs. external Torx vs. hex) against Mercedes-Benz service documentation for the 725.0 transmission. Note the bolt length and positions for reinstallation. Keep bolts organized and clean.
4. 4

   Extract transmission range sensor
   Carefully pull the transmission range sensor straight out from the transmission case. ATF will begin draining immediately from the mounting bore. Allow fluid to drain into the pan for 1-2 minutes. Inspect the sensor for physical damage, fluid contamination on the electrical connector pins, or obvious wear on the mounting flange.
5. 5

   Inspect mounting bore and remove old seal
   Inspect the transmission case mounting bore for debris, metal particles, or damage to the sealing surface. Remove the old O-ring seal from the transmission case bore (it may remain in the bore or come out attached to the old sensor). Clean the mounting bore and sealing surface with a clean shop rag. Do not use solvents that could contaminate the transmission fluid.
6. 6

   Prepare new transmission range sensor
   Install the new O-ring seal onto the new transmission range sensor, ensuring it is properly seated in the sensor groove. Lightly lubricate the O-ring with clean MB 236.17 ATF to ease installation. Verify the sensor mounting flange is clean and free of debris. Inspect the new sensor electrical connector for any shipping damage or contamination.
7. 7

   Install new transmission range sensor
   Align the transmission range sensor with the mounting bore and carefully insert it into the transmission case. The sensor will have a specific orientation with alignment features on the housing. Push the sensor fully into the bore until the mounting flange contacts the transmission case. Ensure the O-ring does not roll or pinch during installation.
8. 8

   Install and torque sensor mounting bolts
   Install the 2 transmission range sensor mounting bolts by hand, threading them in several turns to ensure proper engagement. Torque the mounting bolts to the Mercedes-Benz specified value (verify exact torque in WIS for the 725.0 sensor fasteners) using a torque wrench. Do not overtighten. Do not overtighten, as this can damage the sensor housing or transmission case threads.
9. 9

   Reconnect electrical connector
   Connect the electrical connector to the transmission range sensor, ensuring it clicks fully into the locked position. Verify the locking tab is properly engaged. Gently tug on the connector to confirm it is secure.
10. 10

    Add replacement transmission fluid
    From the transmission dipstick tube or fill port (depending on your specific transmission configuration), add the appropriate quantity of the Mercedes-Benz specified ATF (verify correct sheet — typically MB 236.15/236.16 for the 725.0 9G-TRONIC) to replace the fluid lost during the procedure. The 9G-TRONIC transmission requires precise fluid level, so this will be verified during the final fluid level check procedure.
11. 11

    Reinstall undertray panels
    Reinstall all engine undertray panels and secure with their Torx fasteners. Ensure all panels are properly aligned and all fasteners are tightened securely.
12. 12

    Reconnect battery and perform transmission adaptation
    Reconnect the negative battery terminal. Connect Mercedes-Benz STAR Diagnosis or equivalent diagnostic scanner. Clear all stored transmission fault codes. Perform the transmission range sensor adaptation/calibration procedure as specified by Mercedes-Benz. This typically involves a guided procedure where the system learns the sensor position in each gear. Follow the on-screen instructions, which will require cycling through each gear position (P, R, N, D) with the engine running.
13. 13

    Verify transmission fluid level and perform test drive
    With the engine running and transmission at operating temperature (approximately 80°C/176°F), verify the transmission fluid level using the proper Mercedes-Benz procedure for the 9G-TRONIC. This typically requires the diagnostic scanner to monitor transmission temperature while checking level. Add or remove ATF as necessary to achieve proper level. Perform a comprehensive test drive including all gear ranges, checking for proper gear display on the instrument cluster, smooth shifting, and no fault codes.

Reassembly

1. Reinstallation follows the reverse order of removal with attention to proper torque specifications.
2. The transmission range sensor adaptation procedure is mandatory after replacement — the TCU must learn the new sensor's position values.
3. Proper transmission fluid level verification requires the transmission to be at operating temperature and typically requires a diagnostic scanner to monitor temperature accurately.

Verification

• Start the engine and verify the gear position display on the instrument cluster matches the physical gear selector position in all ranges (P, R, N, D).
• Use diagnostic scanner to verify no transmission fault codes are present after adaptation procedure.
• Verify the vehicle will only start in Park and Neutral positions (neutral safety switch function).
• Verify reverse lights illuminate when shifted into Reverse.
• Perform test drive and confirm smooth shifting through all gears with no harsh engagements or delayed shifts.
• Inspect transmission range sensor area for any ATF leaks after test drive.
• Verify transmission fluid level is correct at operating temperature using proper Mercedes-Benz procedure.

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