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Pelican Technical Article:

Alternator Replacement

Steve Vernon

Time:

1 hour1 hr

Tab:

$400

Talent:

**

Tools:

E12 Torx, 13mm socket, screwdriver, floor jack, jack stands, wheel chocks, safety glasses, torque wrench

Applicable Models:

Mercedes-Benz C350 (2008-15)
Mercedes-Benz GLK350 (2010-15)

Parts Required:

New or rebuilt alternator

Hot Tip:

ALWAYS disconnect the battery before beginning

Performance Gain:

Car charges again

Complementary Modification:

Change the drive belt

The alternator charges the battery and provides your car with a constant source of electricity while the engine is running. Over time, the alternator will begin to fail and cause trouble with the various electrical devices in the car. If you suspect alternator trouble, you need to check to see that it is operating correctly, and is indeed the cause of the problems with your charging system. Sometimes, bizarre electrical problems can be caused by a number of faults other than the alternator. It's important to troubleshoot the system prior to replacing your alternator.

Inspect the belt that drives the alternator. Is it tight and amply turning the alternator? If not, then check that the belt tensioner is working correctly. Modern belts seldom break, but they get brittle and glazed with age, and can slip on their pulleys. Replace the belt with a new one as required.

The next item to check is the voltage at the battery. Before performing any tests of your alternator, charge and test your battery. If the battery is faulty, your alternator tests will not be accurate. This should read a little more than 12 volts with the engine off. Next check the voltage of your charging system under load, the voltage should be within 13.2: 14.5 volts d/c. To load, have the engine running at idle, turn on the headlights and the HVAC blower motor. Never disconnect a battery cable while the engine is running to test the alternator, you may cause damage to the alternator or other electrical components from the surge in amperage. If your battery appears to be leaking, then your voltage regulator has probably failed.

The battery will usually only leak acid if it has been overcharged at a much higher voltage. If the voltage measured at the battery is more than 14.5 volts when the engine is running, then the regulator is probably bad. If your battery has boiled over and has acid overflowing out the top, make sure that you clean up any spilled acid immediately. Dousing the area with a water and baking soda solution should help considerably to neutralize the acid and prevent it from eating away at the metal.

An important item to check on your car is the engine ground strap. The engine is electrically isolated from the chassis by rubber motor mounts. If the engine ground strap is damaged or disconnected, you will have problems, including electrical system malfunctions and/or difficult starter cranking.

If you've checked all of these things and you still have charging problems, it's likely the alternator will need to be replaced.

You will need to safely raise and support the vehicle; please see our article on safely raising and supporting your vehicle for additional instructions.

The first step in replacing any alternator is to disconnect the battery.
Figure 1

The first step in replacing any alternator is to disconnect the battery. You will be working around live electric wires here. If you happen to touch the lead going to the alternator against something, you can cause permanent damage to the electrical system and yourself if the battery is hooked up. Be smart here and disconnect it. Please refer to our article on battery replacement for more info.

You need to remove the drive belt; this picture shows the routing of the belt around the power steering pump (green arrow), the A/C compressor (yellow arrow) and the alternator (red arrow).
Figure 2

You need to remove the drive belt; this picture shows the routing of the belt around the power steering pump (green arrow), the A/C compressor (yellow arrow) and the alternator (red arrow). You can use this image for directions when reinstalling the belt at the end of the job.

Place a 17mm socket over the nub on the tensioner and turn it counter clockwise.
Figure 3

Place a 17mm socket over the nub on the tensioner and turn it counter clockwise. This will loosen the belt and allow you to slip it off the pulleys (red arrow). Use care not to get your fingers pinched between the belt and pulleys.

You will need to remove the lower engine trays to access the alternator on the lower right side of the engine (red arrow).
Figure 4

You will need to remove the lower engine trays to access the alternator on the lower right side of the engine (red arrow). Please see our article on under body tray removal for additional assistance.

Use a 13mm socket and remove the power steering line (red arrow) from the lower mount on the alternator.
Figure 5

Use a 13mm socket and remove the power steering line (red arrow) from the lower mount on the alternator. Next use an E12 Torx and remove the two lower mounting bolts (yellow arrows). The forward bolt does not have enough clearance to be fully removed and will remain in the alternator until you have removed the upper bolts.

Looking up between the steering rack and sub-frame you can see the rear of the alternator.
Figure 6

Looking up between the steering rack and sub-frame you can see the rear of the alternator. There is a plastic cap over the main wire going to the back of the alternator (red arrow); remove the cap and then use a 13mm socket to remove the nut holding the wiring harness to the alternator. There is also a plug (yellow arrow) that needs to be disconnected but I found this easier to do from above.

Working from above you can squeeze in the tab on the wiring connection and pull it off the alternator (red arrow).
Figure 7

Working from above you can squeeze in the tab on the wiring connection and pull it off the alternator (red arrow). If your vehicle still has the zip tie holding the wiring loom in place on the alternator mount use a set of cutters and cut it using care not to cut the loom (yellow arrow).

Next use the E12 Torx socket and remove the two upper mounting bolts (red arrows).
Figure 8

Next use the E12 Torx socket and remove the two upper mounting bolts (red arrows).

With a little wiggling and work you can remove the alternator from the engine.
Figure 9

With a little wiggling and work you can remove the alternator from the engine.

Installation is the reverse of removal.
Figure 10

Installation is the reverse of removal. Do not forget to install the power steering line bracket and forward mounting bolt before you start bolting the alternator in place, or you will need to remove it to fit the pieces.

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