Fuse Box - Engine Bay

Removal and replacement of the engine bay fuse box (SAM module) on a 2019 Mercedes-Benz G-Class with 4.0L Turbo V8 engine, including disconnection of electrical connectors and mounting hardware.

Warnings

Tools required

Parts

• Engine bay fuse box (SAM module) × 1 — Use OEM specification
• Fuse box cover seal (if damaged) × 1 — Use OEM specification

Preparation

1. Park vehicle on level ground and engage parking brake
2. Turn ignition off and remove key fob from vehicle interior
3. Open hood and secure with prop rod
4. Allow engine to cool completely if recently operated
5. Locate the engine bay fuse box on the driver's side of the engine compartment, near the inner fender
6. Photograph the fuse box installation and all visible connectors for reference during reassembly

Procedure

1. 1

   Disconnect Battery Negative Terminal
   Using a 10mm wrench or battery terminal wrench, loosen the negative battery terminal clamp bolt. Remove the negative cable from the battery post and secure it away from the battery to prevent accidental reconnection. Wait a minimum of 10 minutes to allow capacitors in electronic modules to fully discharge before proceeding.
2. 2

   Remove Fuse Box Cover
   Release the cover locking tabs on the fuse box by pressing or lifting the release mechanisms (typically located on the front and sides of the cover). Lift the fuse box cover straight up and away from the housing. Inspect the cover seal for damage or deterioration and set aside for reinstallation or replacement.
3. 3

   Document and Remove Individual Fuses and Relays
   Before disconnecting the fuse box, photograph the fuse and relay positions inside the box. Using the fuse puller tool (typically stored in the fuse box cover or elsewhere in the engine bay), remove all individual fuses and relays from the fuse box. Place them in a labeled container or on a clean surface in their correct positions to maintain organization during reinstallation.
4. 4

   Disconnect Primary Electrical Connectors
   Identify the large multi-pin electrical connectors on the bottom and sides of the fuse box housing. These connectors typically have red or gray locking tabs or sliding locks. Press or slide the locking mechanism away from the connector body while pulling the connector straight out from the fuse box. Disconnect all electrical connectors attached to the fuse box assembly. Verify the exact number and type of connectors against Mercedes WIS for the W463/M176 before removal.
5. 5

   Disconnect Ground Connection
   Locate the ground wire connection on the fuse box housing (typically a bolt with a ring terminal on the side or bottom of the assembly). Using the appropriate socket (verify size against Mercedes WIS; commonly 8mm–13mm on this platform), remove the ground bolt and disconnect the ground wire from the fuse box. Keep the bolt and any washers together for reinstallation.
6. 6

   Remove Fuse Box Mounting Fasteners
   Locate the mounting fasteners securing the fuse box to the body or mounting bracket. The fuse box may be secured by Torx fasteners, hex bolts, or plastic locking clips depending on the exact assembly — verify the fastener type, size, and count against Mercedes WIS for the W463/M176 before removal. Remove all fasteners or release all clips holding the fuse box in place.
7. 7

   Remove Fuse Box Assembly
   Carefully lift the fuse box assembly up and away from its mounting location. The assembly may be held by alignment pins or guides, so lift vertically first to clear these before angling the box out of the engine bay. Check for any additional wiring harness clips or ties that may still be securing the box to the vehicle and release them as needed. Remove the fuse box from the vehicle.
8. 8

   Inspect Mounting Area and Connectors
   With the fuse box removed, inspect the mounting bracket and body mounting points for corrosion, damage, or loose hardware. Inspect all electrical connector pins in the vehicle-side harnesses for corrosion, bent pins, or damage. Clean any corrosion from mounting surfaces and connector housings using electrical contact cleaner. If connector pins show corrosion, clean them carefully with contact cleaner and allow to dry completely.
9. 9

   Install New or Replacement Fuse Box
   Position the new or replacement fuse box assembly into the mounting location, aligning any guide pins or locating features with their corresponding holes in the mounting bracket. Ensure the fuse box is fully seated and flush with the mounting surface before installing fasteners. The connectors should be easily accessible and positioned correctly for connection.
10. 10

    Install Mounting Fasteners
    Install all fuse box mounting bolts by hand, threading them into their mounting points. Once all bolts are started, tighten them in a cross pattern using a torque wrench to the Mercedes-specified torque (verify in WIS; small M6 plastic-carrier fasteners are typically approximately 7-9 Nm — do not over-torque as this can crack the housing). This ensures even pressure distribution and proper seating of the fuse box assembly.
11. 11

    Reconnect Ground Connection
    Reconnect the ground wire to the fuse box housing using the original mounting location. Install the ground bolt with any washers in their original orientation. Tighten the ground bolt to the Mercedes-specified torque using a torque wrench (verify in WIS; M6 ground studs are commonly approximately 8-10 Nm). Ensure the ring terminal is making clean metal-to-metal contact with the mounting surface.
12. 12

    Reconnect Electrical Connectors
    Apply a small amount of dielectric grease to the connector seals if desired (optional but recommended for corrosion protection). Reconnect each electrical connector to the fuse box by aligning the connector with its mating receptacle and pushing firmly until you hear or feel a click. Verify each locking mechanism is fully engaged by gently pulling on the connector body—it should not separate from the fuse box. Reference your photographs to ensure all connectors are attached to the correct locations.
13. 13

    Reinstall Fuses and Relays
    Using your photographs as reference, reinstall all fuses and relays into their correct positions in the fuse box. Ensure each fuse and relay is fully seated in its socket. Verify that the fuse ratings match the markings on the fuse box diagram (typically printed on the inside of the cover or in the owner's manual).
14. 14

    Reinstall Fuse Box Cover
    Inspect the cover seal and replace if damaged or deteriorated. Position the fuse box cover over the fuse box housing, aligning any locating features. Press down firmly on the cover until all locking tabs click into place. Verify the cover is secure by gently attempting to lift it—it should not separate from the housing.
15. 15

    Reconnect Battery and Verify Systems
    Reconnect the negative battery cable to the negative battery post. Tighten the terminal clamp bolt securely using a 10mm wrench. Turn the ignition to the ON position (do not start engine) and verify that the instrument cluster illuminates and no warning lights indicate electrical system faults. NOTE: If a NEW fuse box / front SAM control unit was installed, it will likely require SCN online coding/programming via Mercedes Xentry/DAS before it functions correctly — verify coding requirements before returning the vehicle to service. Check the operation of lights, windows, and other electrical accessories to confirm proper fuse box operation.

Reassembly

1. Reassembly follows removal steps in reverse order
2. Ensure all electrical connectors are fully seated and locked before reconnecting battery
3. Verify fuse and relay positions match the fuse box diagram before closing cover
4. After battery reconnection, reset clock, radio presets, and any other vehicle settings that may have been cleared
5. If vehicle exhibits anti-theft lockout, follow Mercedes-Benz procedures for system reset using security credentials

Verification

• Turn ignition to ON position and verify instrument cluster displays no electrical fault warnings
• Start engine and confirm it runs normally without fault codes
• Test operation of all major electrical systems: headlights, turn signals, windows, climate control, infotainment system
• Use a diagnostic scanner to check for any stored fault codes related to the fuse box (SAM module) or electrical system
• Verify that all fuses and relays are properly seated and providing power to their respective circuits
• Check for any loose connectors or hardware around the fuse box installation area
• Road test vehicle to confirm all electrical systems function normally under driving conditions

Related trouble codes on this vehicle

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