Relay - Generic

Procedure for locating and replacing a faulty relay in the 2007-2013 Mercedes-Benz S65 AMG, which may be located in the engine compartment fuse box, trunk fuse box, or SAM modules depending on the specific relay circuit.

Warnings

Tools required

Parts

• Replacement relay (specific to circuit being repaired) × 1 — Use OEM specification - varies by relay function

Preparation

1. Identify the specific relay requiring replacement using fault codes, wiring diagram, or symptom diagnosis
2. Locate the relay position using the fuse/relay diagram on the fuse box cover or in the owner's manual
3. Turn ignition off and remove key from vehicle
4. For relays in engine compartment: allow engine to cool if recently operated
5. For rear seat or trunk relays: ensure you have access to proper fuse box location

Procedure

1. 1

   Access the relay location
   For engine compartment fuse box: Open hood and locate the fuse/relay box on the left side of engine bay. Remove the cover by releasing the clips. For rear seat fuse box: Fold forward the rear seat cushion to access the SAM module. For trunk fuse box: Open trunk and locate the fuse/relay panel on the right side, remove the access cover.
2. 2

   Locate the specific relay
   Using the relay diagram on the fuse box cover or owner's manual, identify the exact position of the relay to be replaced. Note the relay number and function. Common relays include fuel pump relay (K27), starter relay (K4), cooling fan relays, AC compressor relay, and various lighting relays.
3. 3

   Inspect the existing relay
   Before removal, visually inspect the relay for signs of burning, melting, or corrosion on the terminals. Check surrounding relays and fuses for similar damage which may indicate a larger electrical issue. If widespread damage is present, further electrical diagnosis is required before proceeding.
4. 4

   Remove the faulty relay
   Grasp the relay firmly and pull straight up with steady pressure. If resistance is encountered, use a relay puller tool or gently rock the relay side-to-side while pulling upward. Do not twist or bend the relay excessively as this can damage the socket terminals. Some relays may have a locking tab that must be pressed before removal.
5. 5

   Inspect the relay socket
   Examine the socket terminals for corrosion, burning, or damage. Look inside the socket with a flashlight to ensure all terminals are present and not pushed back. If corrosion is present, clean terminals with electrical contact cleaner and allow to dry. If terminals are damaged or burned, the entire fuse box may require replacement or professional repair.
6. 6

   Verify replacement relay specifications
   Compare the new relay to the old relay. Verify the part number, amperage rating, voltage rating, and pin configuration match exactly. Mercedes-Benz uses various relay types including standard 4-pin, 5-pin change-over, and specialized multi-pin relays. Installing an incorrect relay can cause electrical system damage or fire.
7. 7

   Install the new relay
   Align the relay pins with the socket terminals, ensuring correct orientation. The relay body will typically have an arrow or notch indicating proper alignment. Press the relay firmly into the socket until it seats completely and sits flush with surrounding relays. You should feel a positive click or seating sensation when properly installed.
8. 8

   Reinstall fuse box cover and test operation
   Replace the fuse box cover ensuring all clips are properly engaged. Turn the ignition to position II (all accessories on) without starting the engine. Test the circuit controlled by the relay (lights, fuel pump prime, cooling fans, etc.). Listen for the relay click when the circuit activates. If the relay does not click or the circuit does not function, recheck relay installation and specifications.

Reassembly

1. Ensure all fuse box covers are properly secured to prevent moisture intrusion
2. If rear seat was moved, ensure it locks back into position correctly
3. Verify no tools or parts were left in the engine compartment or trunk area

Verification

• Test the affected circuit multiple times to ensure consistent operation
• Listen for proper relay clicking sound when circuit is activated
• Check for any new warning lights on the instrument cluster
• For fuel pump relay replacement: verify engine starts and runs normally without hesitation
• For cooling fan relays: run engine to operating temperature and verify fans activate
• If problem persists after relay replacement, further electrical diagnosis is required as the relay may not be the root cause

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

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