Alternator

Remove and replace the alternator on the 2007-2013 Mercedes-Benz S65 AMG with 6.0L V12 BiTurbo M275 engine, including serpentine belt removal and electrical connections.

Warnings

Tools required

Parts

• Alternator × 1 — OEM Mercedes-Benz or Bosch AL0892X equivalent, 220A output
• Serpentine belt × 1 — Use OEM specification if existing belt shows wear

Preparation

1. Ensure vehicle is parked on level ground with ignition off and key removed
2. Allow engine to cool for at least 1 hour if recently operated
3. Photograph or diagram the serpentine belt routing before removal for reference
4. Open hood and secure it in the fully open position
5. Gather all tools and position them for easy access

Procedure

1. 1

   Disconnect battery negative terminal
   Locate the battery in the engine compartment. Using a 10mm socket, loosen the negative (-) battery terminal bolt. Remove the terminal from the battery post and secure it away from the battery to prevent accidental reconnection. Wait 5 minutes for system capacitors to discharge.
   Torque spec

   Battery Terminal Bolts8 Nm (6 lb-ft)
2. 2

   Remove engine cover
   The M275 V12 engine has a multi-piece engine cover. Remove the center decorative cover by releasing the quick-release fasteners. Lift the cover straight up and off the engine. Set aside in a clean area.
3. 3

   Document and release serpentine belt tension
   Locate the automatic belt tensioner on the left side of the engine. Using a 16mm wrench or serpentine belt tool, rotate the tensioner clockwise to release tension. While holding tension, slide the belt off the alternator pulley first, then carefully release the tensioner. Remove the belt completely from all pulleys and inspect for wear.
4. 4

   Disconnect alternator electrical connections
   Locate the B+ power cable connection on the rear of the alternator (red protective cover). Lift the protective cover and use a 13mm socket to remove the battery cable nut. Remove the cable and secure it away from the alternator. Disconnect the plug connector for the voltage regulator by pressing the release tab and pulling straight out.
   ⚠Do not allow the B+ cable to contact any ground surface or metal components
5. 5

   Remove alternator mounting bolts
   Locate the upper and lower alternator mounting bolts. Using a 16mm socket with extension, remove the upper alternator mounting bolt completely. Then remove the lower mounting bolt (pivot bolt). Support the alternator with one hand while removing the final bolt to prevent it from falling.
   Torque spec

   Alternator Mounting Bolts50 Nm (37 lb-ft)

   Alternator Pivot Bolt25 Nm (18 lb-ft)
6. 6

   Remove alternator from engine
   With both mounting bolts removed, carefully maneuver the alternator upward and out of the mounting bracket. On the M275 V12, there is limited clearance due to the engine configuration. Tilt the alternator slightly toward the front of the vehicle while lifting. Remove the alternator from the engine bay.
7. 7

   Prepare and install new alternator
   Compare the new alternator to the old unit to verify correct replacement. Clean the mounting bracket surfaces with a wire brush to remove any corrosion or debris. Position the new alternator into the mounting bracket, tilting as needed to clear surrounding components. Align the mounting holes with the bracket.
8. 8

   Install alternator mounting bolts
   Insert the lower pivot bolt first and thread it by hand to hold the alternator in position. Insert the upper mounting bolt and thread by hand. Using a torque wrench and 16mm socket, tighten the upper mounting bolt to 50 Nm (37 lb-ft). Then tighten the lower pivot bolt to 25 Nm (18 lb-ft). Verify the alternator is secure and properly aligned with the belt pulley plane.
   Torque spec

   Alternator Mounting Bolts50 Nm (37 lb-ft)

   Alternator Pivot Bolt25 Nm (18 lb-ft)
9. 9

   Reconnect alternator electrical connections
   Connect the voltage regulator plug connector to the alternator until it clicks into place. Position the B+ power cable over the alternator terminal stud. Install the battery cable nut and tighten to 18 Nm (14 lb-ft) using a 13mm socket and torque wrench. Replace the red protective cover over the B+ terminal.
10. 10

    Install serpentine belt
    Following the belt routing diagram photographed earlier, route the new or existing serpentine belt around all pulleys except the alternator pulley. Using the 16mm wrench, rotate the tensioner clockwise to create slack. While holding the tensioner, slip the belt onto the alternator pulley. Carefully release the tensioner to apply proper tension to the belt. Verify the belt is seated correctly in all pulley grooves.
11. 11

    Reinstall engine cover and reconnect battery
    Replace the engine cover by aligning the quick-release fasteners and pressing down until they click into place. Clean the battery terminals with a wire brush if needed. Reconnect the negative battery terminal and tighten the terminal bolt to 6 Nm (4 lb-ft) using a 10mm socket. Do not overtighten as this can damage the terminal.
    ⚠Battery terminal bolts are low torque specification - overtightening will strip threads or crack the terminal
    Torque spec

    Battery Terminal Bolts8 Nm (6 lb-ft)

Reassembly

1. Ensure all electrical connections are secure and protective covers are in place
2. Verify serpentine belt is properly seated in all pulley grooves and has proper tension
3. Confirm no tools or materials were left in the engine compartment

Verification

• Start the engine and verify the alternator is operating smoothly without unusual noise
• Check that the battery warning light on the dashboard illuminates during start and then turns off
• Use a multimeter to verify charging voltage at battery terminals reads 13.5-14.5 volts at idle with engine running
• Observe the serpentine belt operation for 30 seconds to ensure proper tracking and no slippage
• Turn on electrical loads (headlights, climate control, radio) and verify voltage remains in proper charging range

Related trouble codes on this vehicle

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