Ignition Switch

Replacement of the ignition switch assembly, which interprets steering column key cylinder or start button input to enable engine starting and accessory power modes.

Warnings

Tools required

Parts

• Ignition switch assembly × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and apply parking brake
2. Turn ignition to OFF position and remove key fob from vehicle
3. Open driver's door and leave open throughout procedure
4. Disconnect battery negative terminal at battery located in engine bay passenger side
5. Wait 15 minutes for airbag system capacitors to discharge
6. Adjust steering wheel to lowest and most extended position for maximum access

Procedure

1. 1

   Remove Lower Steering Column Cover
   Locate the lower steering column cover below the steering wheel. Remove the Torx fasteners securing the lower cover (typically 3 fasteners - check along the underside edges and near the hinge point). Carefully pull the lower cover downward and away from the column, releasing any retaining clips at the rear edge. Set cover aside.
2. 2

   Remove Upper Steering Column Cover
   With the lower cover removed, locate the Torx fasteners securing the upper steering column cover (typically 2-3 fasteners accessible from below). Remove these fasteners. Separate the upper cover by lifting it upward and away from the column assembly, working around the key cylinder or start button assembly. The cover may have alignment tabs at the front - slide forward slightly if needed to disengage.
3. 3

   Locate Ignition Switch Assembly
   With column covers removed, identify the ignition switch assembly on the right side of the steering column, typically mounted with a bracket near the key cylinder housing. The switch is a rectangular electrical component with a multi-pin connector (approximately 8-12 pin) attached. Note the routing of the wiring harness for reinstallation reference.
4. 4

   Disconnect Ignition Switch Connector
   Locate the locking tab or release button on the ignition switch connector. Press the release mechanism and carefully pull the connector straight away from the switch body. Do not pull on the wiring - use the connector body itself. If access is restricted, you may need to release any nearby harness clips to gain slack.
5. 5

   Remove Ignition Switch Mounting Fasteners
   Remove the mounting fasteners securing the ignition switch to its bracket. These are typically 2 Torx screws (T20 or T25). Note the orientation of the switch and any alignment features or index marks before removal. Keep track of any washers or spacers. Remove the switch from the column assembly.
6. 6

   Verify Mechanical Linkage Condition
   With the old switch removed, inspect the mechanical actuator rod or cam interface that connects the key cylinder rotation to the switch. Verify this linkage moves freely and shows no wear or damage. Clean any debris from the mounting area. This rod must engage properly with the replacement switch.
7. 7

   Position New Ignition Switch
   Align the new ignition switch to the mounting bracket, ensuring the mechanical actuator rod or cam engages correctly with the switch body. The switch will only fit in the correct orientation - look for alignment tabs or index features. Do not force the switch into position. Verify the actuator engages fully before proceeding.
8. 8

   Install Ignition Switch Mounting Fasteners
   Install the mounting fasteners finger-tight first to ensure proper alignment. Once both fasteners are started and the switch is properly seated, torque the fasteners to specification. Verify the switch does not move once tightened.
9. 9

   Reconnect Ignition Switch Connector
   Route the wiring harness to the new switch, ensuring no pinch points or interference with steering column movement. Align the connector with the switch terminals and press firmly until the locking mechanism clicks into place. Tug gently on the connector to verify it is fully seated and locked.
10. 10

    Reinstall Upper Steering Column Cover
    Position the upper steering column cover over the column assembly, working it carefully around the key cylinder or start button. Ensure any alignment tabs engage properly at the front of the cover. Install the Torx fasteners and tighten securely but do not overtorque plastic mounting bosses.
11. 11

    Reinstall Lower Steering Column Cover
    Position the lower steering column cover and align with the upper cover and column assembly. Ensure all retaining clips at the rear edge engage properly. Install the Torx fasteners and tighten securely. Verify both cover halves mate properly with no gaps or misalignment.
12. 12

    Reconnect Battery and Initialize System
    Reconnect the battery negative terminal. Before attempting to start the vehicle, cycle the ignition through its operating modes (OFF, accessory, ignition-on) using the Keyless-Go start button or key fob. A new EIS-related component must be coded and personalized to the vehicle using Mercedes XENTRY diagnostic equipment (SCN online coding); simply cycling the ignition will not initialize the module. Check for proper operation of accessory power, dashboard illumination, and starter engagement.

Reassembly

1. Ensure all steering column covers are properly secured with no gaps or rattles
2. Verify wiring harness has adequate slack and is routed clear of moving steering components
3. Confirm all Torx fasteners are installed and properly tightened

Verification

• Turn ignition to ACC position - verify radio, power windows, and other accessories operate
• Turn ignition to ON position - verify all dashboard warning lights illuminate as expected
• Start the engine - verify starter engages normally without hesitation or multiple attempts
• Test steering wheel lock function if equipped - turn key to OFF and remove, verify wheel locks when turned
• Scan for fault codes using Mercedes-Benz diagnostic system - clear any communication codes that may have been set during battery disconnect
• Verify no new fault codes are present related to ignition switch or EIS module
• Test all ignition positions through multiple cycles to ensure consistent operation

Related trouble codes on this vehicle

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