Transmission Speed Sensor - Input

This procedure covers the replacement of the input speed sensor on the 722.9 7-speed automatic transmission in the 2007-2013 Mercedes-Benz S65 AMG.

Warnings

Tools required

Parts

• Transmission input speed sensor × 1 — Use OEM specification
• Sensor O-ring seal × 1 — Usually included with sensor
• Transmission pan gasket × 1 — Use OEM specification

Fluids

• Mercedes-Benz ATF 134 — 2.5 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow transmission to cool to ambient temperature if recently driven
3. Raise and safely support vehicle on lift or jack stands rated for vehicle weight
4. Remove engine undertray panels and transmission access covers using T30 Torx bit
5. Place fluid catch pan beneath transmission pan area

Procedure

1. 1

   Drain partial transmission fluid
   Locate the transmission drain plug on the bottom of the pan. Using a 13mm socket, carefully remove the drain plug and allow approximately 2-3 quarts of fluid to drain into the catch pan. Install the drain plug with a new crush washer if equipped.
   Torque spec

   Transmission Drain Plug30 Nm (22 lb-ft)
2. 2

   Remove transmission pan bolts
   Using a 10mm socket, remove all transmission pan bolts in a criss-cross pattern starting from the outer edges working inward. There are approximately 13 bolts securing the pan. Keep track of bolt locations as some may be different lengths.
   ⚠Additional fluid (approximately 1 quart) will drain when pan is lowered. Ensure catch pan is positioned correctly.
   Torque spec

   Pan Bolts22 Nm (16 lb-ft)
3. 3

   Lower and inspect transmission pan
   Carefully lower the transmission pan and pour remaining fluid into catch pan. Inspect pan for metal shavings or debris (small amount of fine material is normal). Inspect magnet for excessive metal particles. Clean pan thoroughly and remove old gasket material from both pan and transmission housing.
4. 4

   Locate input speed sensor
   With pan removed, locate the input speed sensor (Y3/6n1) on the valve body. It is positioned on the driver's side of the transmission, near the front section of the valve body. The sensor has a black electrical connector and is secured by a single bolt.
5. 5

   Disconnect electrical connector
   Press the locking tab on the electrical connector and carefully disconnect it from the input speed sensor. If connector is difficult to remove, use a pick or small screwdriver to release the secondary lock if equipped. Inspect connector terminals for corrosion or damage.
6. 6

   Remove input speed sensor
   Using a 10mm socket, remove the sensor mounting bolt. Carefully pull the sensor straight out from the valve body housing. Note the orientation of the sensor for installation of the new unit. Remove and discard the old O-ring seal from the sensor bore.
   ⚠Do not pry against valve body or use excessive force. Sensor should pull out with gentle pressure.
   Torque spec

   Sensor Bolts15 Nm (11 lb-ft)
7. 7

   Prepare new sensor for installation
   Remove new input speed sensor from packaging. Verify new O-ring seal is present on sensor. Lightly lubricate O-ring with clean ATF 134 transmission fluid to ease installation. Inspect sensor electrical terminals for any shipping damage.
8. 8

   Install new input speed sensor
   Align new sensor with bore in valve body, ensuring proper orientation matches original sensor position. Press sensor firmly into place until fully seated. Install sensor mounting bolt and tighten to specification.
   Torque spec

   Sensor Bolts15 Nm (11 lb-ft)
9. 9

   Reconnect electrical connector
   Push electrical connector onto new sensor until locking tab clicks into place. Verify connection is secure by gently pulling on connector. Ensure wiring is routed away from any moving components or sharp edges.
10. 10

    Install new transmission pan gasket and pan
    Position new gasket onto transmission housing, ensuring all bolt holes align correctly. Lift transmission pan into position and start all bolts by hand. Tighten pan bolts in criss-cross pattern from center outward to specification.
    Torque spec

    Pan Bolts22 Nm (16 lb-ft)
11. 11

    Refill transmission fluid
    Through the transmission fill tube (accessed from engine bay near firewall), add approximately 2.5 quarts of Mercedes-Benz ATF 134 fluid using appropriate funnel. Start engine and allow to idle in Park. Shift through all gear positions, pausing 3 seconds in each position, then return to Park.
    ℹ️Transmission fluid level must be checked at operating temperature. Initial fill is approximate only.
12. 12

    Check fluid level and verify operation
    With engine running and transmission at operating temperature (80-100°C), check fluid level through fill plug or dipstick per manufacturer specification. Add fluid as needed. Using diagnostic scan tool, verify input speed sensor is reading correctly and no fault codes are present.

Reassembly

1. Reinstall transmission access covers and engine undertray panels, tightening all fasteners securely
2. Lower vehicle to ground and verify no fluid leaks from transmission pan or drain plug
3. Clear any transmission adaptation values using Mercedes-Benz diagnostic equipment to allow transmission to relearn shift patterns with new sensor data

Verification

• Start engine and verify no transmission warning lights illuminate on instrument cluster
• Road test vehicle through all gears, verifying smooth shifts and proper gear engagement
• Using diagnostic scan tool, verify input speed sensor voltage/frequency signal is present and within specification (typically 0-5V pulsing signal)
• Recheck transmission fluid level after vehicle reaches full operating temperature
• Inspect underneath vehicle for any fluid leaks after test drive

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