How do I replace an alternator?
By Cheryl B
The alternator is part of the charging system on a vehicle. In many cases, it is easy enough to remove and replace the alternator, but on some vehicles, you may not be able to access the bolts without removing other parts. If you need to do this, be sure you have the instructions to remove the parts that are in the way. Label wires and hoses so you know where to put them when you put everything together.
Also, before you start, locate the belt diagram. If your vehicle’s belt diagram sticker is missing from the hood or radiator shroud, sketch the belt’s routing before you take it off, especially if your vehicle uses a serpentine belt that is routed around all of the pulleys.
Before you put your hands into the engine compartment, remove the positive battery cable. It is always a good idea to tag the wires going to the back of the alternator. If you attach the wires in the wrong place, you could fry the alternator and the store and manufacturer won’t cover that mistake under warranty.
Remove the serpentine belts or V-belts. If your vehicle has V-belts, remove only the belts needed. Usually V-belts use a slider to put the proper tension on the belt. Simply loosen the slider bolt, push the alternator toward the center of the engine and lift the belt off the pulley. You do not need to remove the belt from the other pulleys.
If your vehicle has a serpentine belt, rotate the belt tensioner toward the center of the engine. This will provide enough slack so that you can remove the belt from the alternator pulley. You can leave the belt on the rest of the pulleys if you don’t have to remove one of the other accessories.
Unplug the alternator wiring harness connector. Remove the nut holding the power wire onto the alternator. Set the wire aside, then put the nut back on the stud for now — just so you don’t lose it. Remove the alternator and set it aside. Don’t throw it away — most places charge you a core charge, which you get back when you bring it into the store.
Install the new alternator. Reinstall the belts. Reattach the alternator’s wiring -- get the nut for the stud from the old alternator. Reinstall any other parts you may have had to remove to complete the alternator replacement. Reinstall the belts. Tighten the belts. If you have V-belts, tighten the belts until you can twist the belt 90 degrees. If the belts won’t tighten, make sure you have them on the right pulleys. If they still won’t tighten, the belts need to be replaced because they stretched.
If you have a serpentine belt, install it around all of the pulleys except the tensioner. Rotate the tensioner toward the center of the engine and slide the belt over the tensioner. Make sure the marks on the tensioner are in the correct range. If they are not, replace the serpentine belt — it stretched so far that the tensioner won’t tighten it.
Reattach the battery positive cable. Start the vehicle and using a voltmeter, be sure the alternator is charging the battery. The battery must have at least 12 volts before you start the vehicle or it will look like the alternator is not charging. Furthermore, you could damage the alternator if you try to charge a completely dead battery by running the vehicle. Use a battery charger to charge the battery. If everything checks out, the alternator should be putting out between 13.5 and 14.5 volts when the vehicle is running.
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