Electric Power Steering Module

This procedure covers the removal and replacement of the electric power steering module on the 2007-2013 Mercedes-Benz S65 AMG, including disconnection of electrical connections, hydraulic lines, and steering linkage components.

Warnings

Tools required

Parts

• Electric Power Steering Module × 1 — Use OEM specification
• Power steering line O-rings × 4 — Use OEM specification
• Tie rod end cotter pins × 2 — Use OEM specification
• Protective caps for open hydraulic fittings × 4 — Generic

Fluids

• Pentosin CHF 11S — 1 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect negative battery terminal and wait 10 minutes for system capacitors to discharge
3. Turn steering wheel to center position and lock in place with steering wheel holder or seatbelt
4. Raise front of vehicle and secure on jack stands at manufacturer-specified lift points
5. Remove both front wheels
6. Place drain pan beneath power steering module and lines
7. Take photos of all electrical connections and hydraulic line routing for reference

Procedure

1. 1

   Remove engine undercover and access panels
   Remove the front engine undercover using appropriate socket. Remove plastic access panels in wheel wells to expose steering components. Keep all fasteners organized for reinstallation.
2. 2

   Disconnect tie rod ends from steering knuckles
   Remove cotter pins from tie rod end castle nuts and discard. Loosen but do not remove castle nuts. Use tie rod end puller to separate tie rod ends from steering knuckles. Remove castle nuts completely once ball joints are freed. Keep tie rods attached to steering rack.
   ⚠Do not strike tie rod ends with a hammer as this can damage the ball joint threads and seals.
3. 3

   Disconnect electrical connections from steering module
   Locate all electrical connectors on the power steering module (typically 2-3 connectors). Press release tabs and carefully disconnect each connector. Use electrical contact cleaner on terminals if corrosion is present. Secure connectors away from work area.
4. 4

   Depressurize and drain power steering system
   Start engine briefly and turn steering wheel lock to lock 3-4 times to circulate fluid, then turn off engine. Allow system to sit for 5 minutes to depressurize. Loosen reservoir cap slowly to release any remaining pressure. Position drain pan beneath module.
   ⚠️Fluid may spray when fittings are loosened. Wear safety glasses and have rags ready to contain spillage.
5. 5

   Disconnect hydraulic lines from steering module
   Using brake line wrenches, carefully loosen power steering line fittings at the module. Expect fluid drainage. Remove pressure and return lines, capping open ports immediately with protective caps to prevent contamination. Inspect O-rings on disconnected lines and discard old O-rings.
   ⚠Keep hydraulic fluid away from painted surfaces and electrical components. Clean any spills immediately with approved cleaner.
6. 6

   Remove steering rack mounting bolts
   Support the steering rack with a transmission jack or secure support. Locate and remove steering rack mounting bolts from the subframe. There are typically 2-4 mounting points depending on configuration. Lower steering rack assembly slightly to access module mounting.
   ⚠The steering rack assembly is heavy (approximately 25-30 lbs). Ensure adequate support before removing mounting bolts.
7. 7

   Remove power steering module mounting bolts
   Locate the power steering module mounting bolts securing it to the steering rack or subframe. Remove mounting bolts while supporting the module. Carefully maneuver the module out of the engine bay, being careful not to damage surrounding components or wiring harnesses.
8. 8

   Prepare new power steering module for installation
   Unpack new steering module and verify part number matches old unit. Install new O-rings on all hydraulic line fittings, lubricating lightly with Pentosin CHF 11S. Do not reuse old O-rings. Inspect mounting surfaces and clean with wire brush if necessary.
9. 9

   Install new power steering module
   Position new module into mounting location, aligning bolt holes with rack or subframe. Install mounting bolts finger-tight initially to allow for alignment adjustment. Torque mounting bolts to specification in a cross-pattern.
10. 10

    Reinstall steering rack to subframe
    Raise steering rack assembly into position using support jack. Align mounting bolt holes with subframe. Install steering rack bolts and torque to specification. Ensure rack moves freely through its full travel before proceeding.
11. 11

    Reconnect hydraulic lines
    Remove protective caps from hydraulic ports. Connect pressure and return lines to steering module, ensuring proper routing matches original configuration. Hand-tighten fittings first, then torque to specification using brake line wrenches. Double-check that new O-rings are properly seated.
12. 12

    Reconnect electrical connections and tie rod ends
    Reconnect all electrical connectors to steering module, ensuring positive clicks. Connect tie rod ends to steering knuckles and install new castle nuts. Torque castle nuts to specification and install new cotter pins. Ensure cotter pins are properly bent to prevent loosening.
13. 13

    Fill and bleed power steering system
    Fill power steering reservoir with Pentosin CHF 11S to MAX mark. With engine off, turn steering wheel slowly lock to lock 10 times. Check fluid level and add as needed. Start engine and repeat lock to lock procedure 5 times. Check for leaks at all connections. Top off fluid to proper level.
    ℹ️Air in the system will cause noise and reduced steering assist. Bleeding may take 15-20 minutes and multiple cycles to completely remove air.
14. 14

    Perform system calibration with Star Diagnostic System
    Connect Mercedes-Benz Star Diagnostic System to vehicle OBD-II port. Navigate to steering system module and perform steering angle sensor calibration and power steering module initialization. Follow on-screen prompts to complete calibration with wheels pointed straight ahead. Clear any stored fault codes.
    ⚠️Vehicle must not be driven until steering system calibration is complete. Uncalibrated steering can result in erratic assist levels and potential loss of control.

Reassembly

1. Reinstall wheel well access panels and front engine undercover, torquing cover screws to specification
2. Install front wheels and torque lug nuts to 183 Nm (135 lb-ft) in star pattern
3. Lower vehicle to ground and reconnect negative battery terminal
4. Verify power steering fluid level one final time after test drive

Verification

• Start engine and verify no warning lights related to steering system are illuminated
• Turn steering wheel lock to lock while stationary and verify smooth operation with no unusual noises
• Perform test drive at low speed in safe area, verifying steering assist is functioning properly and wheel returns to center
• Inspect all hydraulic connections for leaks after test drive
• Verify steering angle sensor reads 0 degrees with wheels straight ahead using Star Diagnostic System
• Perform front wheel alignment to verify toe settings are within specification after tie rod disconnection

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