Mercedes-Benz Cars 2000-05

Alternator

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Diagnosis & Testing



Alternator Load Test
  1. Before servicing the vehicle, refer to the Precautions Section.
  2.  
  3. With the engine running, turn on the blower motor and the high beams (or other electrical accessories to place a load on the charging system).
  4.  
  5. Increase and hold engine speed to 2000 rpm.
  6.  
  7. Measure the voltage reading at the battery.
  8.  
  9. The voltage should increase at least 0.5 volts from the voltage test. If the voltage does not meet specifications, the charging system is malfunctioning.
    NOTE
    Usually under and overcharging is caused by a defective alternator, or its related parts (regulator), and replacement will fix the problem; however, faulty wiring and other problems can cause the charging system to malfunction. Many automotive parts stores have alternator bench testers available for use by customers. An alternator bench test is the most definitive way to determine the condition of your alternator.

  10.  

Alternator No-Load Test
  1. Before servicing the vehicle, refer to the Precautions Section.
  2.  
  3. Connect a tachometer to the engine.
    CAUTION
    Ensure that the transmission is in Park and the emergency brake is set. Blocking a wheel is optional and an added safety measure.

  4.  
  5. Turn off all electrical loads (radio, blower motor, wipers, etc.)
  6.  
  7. Start the engine and increase engine speed to approximately 1500 rpm.
  8.  
  9. Measure the voltage reading at the battery with the engine holding a steady 1500 rpm. Voltage should have raised at least 0.5 volts, but no more than 2.5 volts.
  10.  
  11. If the voltage does not go up more than 0.5 volts, the alternator is not charging. If the voltage goes up more than 2.5 volts, the alternator is overcharging.
    NOTE
    Usually under and overcharging is caused by a defective alternator, or its related parts (regulator), and replacement will fix the problem; however, faulty wiring and other problems can cause the charging system to malfunction. Many automotive parts stores have alternator bench testers available for use by customers. An alternator bench test is the most definitive way to determine the condition of your alternator.

  12.  
  13. If the voltage is within specifications, proceed to the next test.
  14.  

Voltage Test
  1. Before servicing the vehicle, refer to the Precautions Section.
  2.  
  3. Make sure the engine is OFF , and turn the headlights on for 15-20 seconds to remove any surface charge from the battery.
  4.  
  5. Using a DVOM set to volts DC, probe across the battery terminals.
  6.  
  7. Measure the battery voltage.
  8.  
  9. Write down the voltage reading and proceed to the next test.
  10.  

Removal & Installation



  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Accessory drive belt
     
    Engine under cover
     
    Alternator electrical wires
     
    Alternator from the bottom of the vehicle
     

  4.  

To install:

  1. Install or connect the following:

    Alternator. Torque the mounting bolts to 31 ft. lbs. (42 Nm).
     
    Alternator electrical wires
     
    Engine under cover
     
    Accessory drive belt
     
    Connect the negative battery cable
     

  2.  
  3. Start the engine and check for proper operation.
  4.  

  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Accessory drive belt
     
    Right inner fender liner
     
    Alternator electrical wires
     
    Alternator
     

  4.  

To install:

  1. Install the alternator assembly. Torque the mounting bolts to 31 ft. lbs. (42 Nm).
  2.  
  3. Install or connect the following:

    Alternator electrical wires
     
    Right inner fender liner
     
    Accessory drive belt
     
    Connect the negative battery cable
     

  4.  
  5. Start the engine and check for proper operation.
  6.  

  1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Accessory drive belt
     
    Engine under cover
     
    Alternator electrical wires
     
    Alternator from the bottom of the vehicle
     

  4.  

To install:

  1. Install or connect the following:

    Alternator. Torque the mounting bolts to 31 ft. lbs. (42 Nm).
     
    Alternator electrical wires
     
    Engine under cover
     
    Accessory drive belt
     
    Connect the negative battery cable
     

  2.  
  3. Start the engine and check for proper operation.
  4.  

2.8L, 3.2L, 3.6L (104), 1.8L, 2.3L (111), 2.6L, 2.8L, 3.2L (112), 4.3L, 5.0L & 5.5L (113) Engines
  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Accessory drive belt
     
    Engine under cover
     
    Alternator electrical wires
     

  4.  
  5. Remove the alternator from the bottom.
  6.  

To install:

  1. Install the alternator assembly. Torque the mounting bolts to 31 ft. lbs. (42 Nm).
  2.  
  3. Install or connect the following:

    Alternator electrical wires
     
    Engine under cover
     
    Accessory drive belt
     
    Negative battery cable
     

  4.  
  5. Start the engine and check for proper operation.
  6.  

2.8L, 3.2L, 3.6L (104), 2.2L, 2.3L (111), 3.2L (112) & 4.3L (113) Engines
  1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Accessory drive belt
     
    Engine under cover
     
    Alternator electrical wires
     

  4.  
  5. Remove the alternator from the bottom.
  6.  

To install:

  1. Install the alternator assembly. Torque the mounting bolts to 31 ft. lbs. (42 Nm).
  2.  
  3. Install or connect the following:

    Alternator electrical wires
     
    Engine under cover
     
    Accessory drive belt
     
    Connect the negative battery cable
     

  4.  
  5. Start the engine and check for proper operation.
  6.  

  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Accessory drive belt
     
    Engine under cover
     
    Alternator electrical wires
     

  4.  
  5. Remove the alternator from the bottom.
  6.  

To install:

  1. Install the alternator assembly. Torque the mounting bolts to 31 ft. lbs. (42 Nm).
  2.  
  3. Install or connect the following:

    Alternator electrical wires
     
    Engine under cover
     
    Accessory drive belt
     
    Connect the negative battery cable
     

  4.  
  5. Start the engine and check for proper operation.
  6.  

4.2L & 5.0L (119) Engines
  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Viscous fan coupling if equipped with ball-type alternator
     
    Accessory drive belt
     
    Alternator electrical connections
     
    Alternator mounting bolts
     
    Alternator
     

  4.  

To install:

  1. Install or connect the following:

    Alternator assembly
     
    Electrical connections
     
    Accessory drive belt
     
    Viscous fan coupling
     
    Negative battery cable
     

  2.  
  3. Start the engine and check for proper operation.
  4.  

  1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Viscous fan coupling if equipped with ball-type alternator
     
    Accessory drive belt
     
    Alternator electrical connections
     
    Alternator mounting bolts
     
    Alternator
     

  4.  

To install:

  1. Install or connect the following:

    Alternator assembly
     
    Electrical connections
     
    Accessory drive belt
     
    Viscous fan coupling
     
    Negative battery cable
     

  2.  
  3. Start the engine and check for proper operation.
  4.  

  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Viscous fan coupling if equipped with ball-type alternator
     
    Accessory drive belt
     
    Alternator electrical connections
     
    Alternator mounting bolts
     
    Alternator
     

  4.  

To install:

  1. Install or connect the following:

    Alternator assembly
     
    Electrical connections
     
    Accessory drive belt
     
    Viscous fan coupling
     
    Negative battery cable
     

  2.  
  3. Start the engine and check for proper operation.
  4.  

6.0L (120) Engine
  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Accessory drive belt
     
    Alternator electrical connections
     
    Automatic transmission coolant pipe
     
    Engine under cover
     
    Right torsion bar and spring leaf rockers
     
    Alternator mounting bolts
     

  4.  
  5. Remove the alternator from the bottom.
  6.  

To install:

  1. Install or connect the following:

    Alternator assembly
     
    Right torsion bar and spring leaf rockers. Torque the bolts to 44 ft. lbs. (60 Nm).
     
    Automatic transmission coolant pipe
     
    Alternator electrical connections
     
    Engine under cover
     
    Negative battery cable
     
    Accessory drive belt
     

  2.  
  3. Start the engine and check for proper operation.
  4.  

  1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Accessory drive belt
     
    Alternator electrical connections
     
    AutoMatic transmission coolant pipe
     
    Engine under cover
     
    Right torsion bar and spring leaf rockers
     
    Alternator mounting bolts
     

  4.  
  5. Remove the alternator from the bottom.
  6.  

To install:

  1. Install or connect the following:

    Alternator assembly
     
    Right torsion bar and spring leaf rockers. Torque bolts to 44 ft. lbs. (60 Nm)
     
    AutoMatic transmission coolant pipe
     
    Alternator electrical connections
     
    Engine under cover
     
    Negative battery cable
     
    Accessory drive belt
     

  2.  
  3. Start the engine and check for proper operation.
  4.  

  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Accessory drive belt
     
    Alternator electrical connections
     
    AutoMatic transmission coolant pipe
     
    Engine under cover
     
    Right torsion bar and spring leaf rockers
     
    Alternator mounting bolts
     

  4.  
  5. Remove the alternator from the bottom.
  6.  

To install:

  1. Install or connect the following:

    Alternator assembly
     
    Right torsion bar and spring leaf rockers. Torque bolts to 44 ft. lbs. (60 Nm)
     
    AutoMatic transmission coolant pipe
     
    Alternator electrical connections
     
    Engine under cover
     
    Negative battery cable
     
    Accessory drive belt
     

  2.  
  3. Start the engine and check for proper operation.
  4.  

Diesel Engine
  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Remove or disconnect the following:

    Negative battery cable
     
    Accessory drive belt
     
    Engine under cover
     
    Alternator electrical wires
     
    Alternator from the bottom of the vehicle
     

  4.  

To install:

  1. Install or connect the following:

    Alternator. Torque the mounting bolts to 31 ft. lbs. (42 Nm).
     
    Alternator electrical wires
     
    Engine under cover
     
    Accessory drive belt
     
    Connect the negative battery cable
     

  2.  
  3. Start the engine and check for proper operation.
  4.  

M111, M112, M113 And M271 Engines
  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. To gain easier access to the alternator, remove or place aside any components in the way such as the air intake tube, engine fan and cooling hoses.
  6.  
  7. Remove the accessory drive belt.
  8.  
  9. Remove the engine under covers.
  10.  
  11. Detach the electrical connections from the alternator.
  12.  
  13. Remove the bolt(s) securing the alternator.
  14.  
  15. Remove the alternator out from the bottom except on CL, S and SL Class; remove it from the top on those models.
  16.  
  17. Installation is the reverse of removal. Tighten the mounting bolts to:

    M271 engines: 15 ft. lbs. (20 Nm)
     
    SL Class and 2003-05 E Class with self tapping screws: 33 ft. lbs. (45 Nm) if holes are tapped, 42 ft. lbs. (57 Nm) if non-tapped.
     
    All others: 31 ft. lbs. (42 Nm).

    Click image to see an enlarged view

    Fig. Exploded view of the alternator mounting-2000-05 E Class, others similar

     

  18.  

M272 Engines
  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Remove the engine under covers.
  6.  
  7. Detach the electrical connections from the alternator.
  8.  
  9. Remove the lower bolts securing the alternator.
  10.  
  11. Remove the engine fan assembly.
  12.  
  13. Remove the accessory drive belt.
  14.  
  15. Remove the upper bolts from the alternator, then take it down and out from the bottom.
  16.  
  17. Installation is the reverse of removal. Tighten the mounting bolts to 15 ft. lbs. (20 Nm).
  18.  

 
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