Alternator Replacement Guide

Got a battery warning light on? This most likely means the alternator has gone out and needs to be replaced. This is a common problem for most vehicles but it isn't as bad as it sounds because most assembly's can be replaced in about an hour using everyday tools. You will be able to save a good chunk of change by changing it yourself or at least know what you are paying for when taking your vehicle into a garage for repair. If you are not sure about the performance of the voltage output of the unit is will need to be tested.

See Also: How to Test an Alternator By watching this video and reading the repair guide below you will gain knowledge if you want to do it yourself or have a garage do the work for you, though appearances may vary the procedure is the same for most vehicles. Once you are done watching the video follow the guide below to get tips and information you may have missed in the video.

You can get a high quality OEM factory such as AC Delco, Motorcraft or Nippon replacement units and a serpentine belt from Amazon for about the same price the repair shops can buy them for. Follow the step by step guide below and get started:

Tools and Supplies Needed

  • Replacement assembly
  • New serpentine belt
  • Basic tool set
  • Protective eye wear and gloves
  • Shop towels
Park your vehicle on level ground with the engine off with the emergency brake on, use a basic set of tools while wearing eye protection and gloves. If needed, raise the vehicle using a floor jack and secure with jack stands.

Step 1

Loosen and remove the negative battery cable, push the cable away from the terminal to avoid accidental connections if the cable wants to wander back over to the terminal. This step is to remove electrical power for the vehicle to avoid short circuits when working with the wiring harness.

Record the radio presets if you want to re-enter them when the job is complete. Avoid removing the positive cable end because it can ground out to the body or accessory while using a wrench.

Step 2

The serpentine belt will need to be removed, located the belt tensioner and hold reverse tension against it using a wrench, socket or breaker bar. This will allow the belt to be removed from the alternator pulley, once the belt has been removed inspect it for cracks and glazing because now would be a good time to replace it with a new one.

Step 3

Remove the dust boot from the main power terminal to expose the main power wire. If the wiring is difficult to access, you will be able to disconnect the wiring once the alternator is loose from the engine. All alternators are designed with a main power cable (large gauge) that is connected directly to the battery for main charging purposes.

Step 4

Using a socket or wrench remove the nut by turning it counterclockwise. After the nut has been removed, grasp the main power cable and lift it from the alternator charge terminal.

Step 5

Next, locate the wiring harness, grasp the dust boot and pull it back enough to access the electrical connector.

Step 6

While releasing the safety clip on the side of the connector, gently pull to outward to remove the wiring harness. These connectors can be stuck because of the weather pack seal which you might need to wiggle to remove.

Step 7

Clear any hoses or wiring by removing mounting bolts or screws, once completed use a wrench or socket to remove the upper mounting bolt and bracket.

Step 8

Locate and remove the lower mounting bolt. This bolt can be a little tight so keep a good grip on the wrench or socket while placing the wrench or socket firmly on the head of the bolt.

Step 9

After the mounting bolts have been removed, grasp the unit and move it back and forth while pulling upward, this will help release the press fit (lower mounting bracket) used to hold the alternator in place.

Step 10

Once the old unit becomes loose in the engine bay, get a good grip in on it to gently lift and remove it. This step can take some trial and error while rotating the unit while some minor adjustments (loosen) to surrounding fan shrouds or radiator hoses that may get in the way of the removal.

Step 11

Once removed, check the old assembly to the replacement unit, including electrical plug, mounting bolt locations and pulley size to ensure a proper installation. Also count the grooves on each of the pulleys they should be the same.

Step 12

Most lower mounting brackets include a press fit sleeve that must be forced slightly outward to make room for the replacement unit, this step is important because installing the new unit would be very difficult if not impossible without this step.

Step 14

Using a large punch gently or metal bar to hammer the sleeve outward. This can take a little finesse but stay with it because it only needs to be moved a little bit to get the lower bolt installed.

Step 15

Here is a close up shot of what the job should look like when completed, now the lower boss of the housing will slip onto position easily.

Step 16

Gently lower the replacement unit into the engine bay while being carefully not the damage any of the surrounding components such as the radiator. The radiator core is made of thin aluminum and it can be easily damaged which would not make your day if you cause a leak.

Step 17

Once the replacement unit is in place reinstall the lower mounting bolt, leave the bolt hand tight until the installation of the upper bolt. If you tighten the lower bolt first the upper bolt might bind which can cause the bolt to strip out.

Step 18

Now hand thread in the upper mounting bolt and tighten, then tighten the lower bolt as well. These bolts need to be snug but don't over tighten which can cause the bolts to strip out especially the upper mounting bolt because it's smaller is size.

Step 19

After the mounting bolts are tightened, reinstall the computer wiring harness that monitors the voltage output along with the rubber weather boot, be sure the connector is free from dirt and grease.

Step 20

Reinstall the main charge cable and mounting nut, gently tighten the cable into place and do not over tighten. This electrical terminal this made of a hard plastic and is used as an insulator which can break causing an internal short hindering the charging operation. Reinstall the rubber weather boot to keep any moisture from entering the connection which will cause corrosion and more problems further down the line.

If the wring harness has mounting clip reinstall them to keep the harness from wearing through and touching ground which will blow the charging system fuse and possibly damage the new unit.

Step 21

Next, reinstall any hoses or brackets removed in the replacement process.

Step 22

After checking the conditioner of the serpentine belt and replacing it if needed, reinstall the belt. Do this by holding tension against the tensioner and then release it once the belt has been routed and in place. If you are confused by the routing of the belt which happens to the best of us, use a belt routing diagram made for your vehicle.

After the belt installation is complete use a flashlight to check the position of the belt on each one of the accessory pulleys to make sure all of the belt ribs are correctly positioned.

Step 23

Now you are ready to connect the battery negative cable back up gently touch the cable to the battery post, there should be a small spark while installing the cable end to the terminal then tighten the cable end. If a large spark is generated the alternator charge cable has grounded and needs to be rechecked, do not reconnect the battery cable until this problem has been fixed. It doesn't happen very often but it's something you should know.

When the job has been completed start the engine and observe the battery warning light which should be out. It's a good idea to check the new alternator's voltage output using a voltmeter. Learn more

How it works

An alternator is designed to supply electrical power (13.6 to 14.6 volts) to a vehicle when the engine is operating while charging the battery for future use.

A serpentine belt is used to deliver rotation from the engine via the main drive pulley.

A large power terminal is used as the main voltage feed to the electrical system which is usually connected to the positive battery post or fuse box, most units are designed with a built in voltage regulator which helps stabilize the voltage output.

This main power feed is used to power circuits throughout the vehicle.

A wiring harness connector is used by the computer PCM to control and monitor the voltage regulator during variable engine speeds (RPM's) and voltage demands.

The assembly works on the principle of electromagnetism, by turning the magnetic armature inside a wire field which has been electrified to produce AC (alternating current) voltage. A series of diodes (6) convert AC to DC voltage which is needed for the electrical system. An armature is supported by two roller bearings on either end of the housing, voltage is transferred to terminals at the rear of the housing via a spring loaded brush set.

Helpful Information

A common problem is undercharging, this condition is often accompanied by symptoms such as a battery warning light, low state of battery charge, poor or erratic performance from electrical components.

Common Problems

  • Unit will overheat due to extreme usage causing a failure.
  • Poor battery condition can cause failure.
  • Weak voltage can cause the battery to slowly drain.
Best Practices

  • Once jump started a severely discharged battery can cause failure and overload the unit and fail internally, if this occurs replace or recharge the battery.
  • A serpentine belt must be in good condition
  • Clean battery terminals regularly
If you need more information on what you have just seen or read please visit our forum where our online mechanics have answered thousands of alternator questions about this subject.

Article first published