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Pelican Technical Article:

Alternator Replacement

Jared Fenton

Time:

1 hour1 hr

Tab:

$300

Talent:

****

Tools:

8mm/13mm/24mm sockets, small standard screwdriver, pliers

Applicable Models:

Jetta MkIV 2.0L (1998-05)

Parts Required:

Alternator

Hot Tip:

Be careful not to damage the electrical connectors

Performance Gain:

Better working electrical system

Complementary Modification:

Replace serpentine belt

The alternator provides your car with a constant source of electricity while the engine is running. Over time, the alternator can begin to fail and start causing trouble with the various electrical systems in the car. If you suspect alternator trouble, you need to check to see that it's 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.

The first thing to check is the belt that drives the alternator. Is it tight? 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.

The next item to check is the voltage at the battery. This should read a little more than 12 volts with the engine off. When the car is running, the voltage should read in the range of 13 to 14.5 volts with the engine at 2000 rpm. 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 16 or 17 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.

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

Before starting any work, make sure that you disconnect the battery. The positive battery terminal is directly connected to the alternator, and it can be dangerous to work on if it's live. See our article on Battery Replacement for more information.

This project also requires removing the serpentine belt. See our article on Serpentine Belt Replacement for more information.

Before starting, it is vitally important that you disconnect the negative terminal from the battery.
Figure 1

Before starting, it is vitally important that you disconnect the negative terminal from the battery. Loosen the 10mm nut on the negative battery clamp (green arrow) and pull the terminal off. Make sure that the terminal can't accidentally touch the battery.

Loosen and remove the top 13mm bolt (green arrow) holding the alternator in place.
Figure 2

Loosen and remove the top 13mm bolt (green arrow) holding the alternator in place.

Now loosen and remove the lower 13mm bolt holding the alternator in place.
Figure 3

Now loosen and remove the lower 13mm bolt holding the alternator in place.

Move to the rear of the alternator and remove the plastic cover (yellow arrow) over the positive lead with a pair of pliers.
Figure 4

Move to the rear of the alternator and remove the plastic cover (yellow arrow) over the positive lead with a pair of pliers. Press the tab on the electrical connector (green arrow) and pull it off.

Loosen and remove the 13mm nut (green arrow) holding the positive lead to the alternator.
Figure 5

Loosen and remove the 13mm nut (green arrow) holding the positive lead to the alternator. Make sure you disconnect the negative lead from the battery before doing this.

Now pull the alternator out of the mounting bracket and turn it over.
Figure 6

Now pull the alternator out of the mounting bracket and turn it over. Use an 8mm wrench to loosen and remove the nut (green arrow) holding the wiring harness (yellow arrow) to the alternator casing.

In some cases, you'll need to transfer the pulley from the old alternator to the new one.
Figure 7

In some cases, you'll need to transfer the pulley from the old alternator to the new one. The easiest way to do this is with an impact wrench or driver. Just zap the 24mm nut (green arrow) off the shaft. If you don't have an impact, you'll need to counter hold the shaft with a T50 Torx driver (green arrow) while using a deep, offset 24mm wrench to loosen the nut. Installing the new alternator is the reverse of removal.


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