Haynes Tech Tips - Alternator Replacement
Your alternator provides the electrical current necessary to keep your battery charged. When your alternator malfunctions, the charging light on your dash will usually be on or the gauge will indicate a discharge. Also, you will likely have starting problems (the engine cranks slowly or will not crank at all). Keep in mind that other problems, such as a bad battery or starter, may produce some similar symptoms. It’s best to have your charging and starting systems checked before assuming the alternator is at fault.
Disconnecting the battery is a necessary part of this procedure. Computers in some vehicles must “re-learn” certain operating data after the battery has been disconnected. On these vehicles, specific procedures must be followed to ensure normal operation after the battery is re-connected. See your service manual for details on your particular vehicle.
- Purchase a service manual for your vehicle. It contains essential information for getting the job done safely and correctly the first time.
- Open the hood. The alternator is located at the drivebelt end of the engine (it is driven by the belt). Most often the alternator is high on the engine and accessible from under the hood. Sometimes, however, access is easier from underneath the engine compartment, requiring the vehicle to be raised and supported securely on jackstands.
- Check the belt to be sure it is tight and in good condition. A damaged or slipping belt will cause the alternator to malfunction.
- Disconnect the cable from the negative terminal of the battery (see Caution above).
- Note how the drivebelt is routed, then remove it. On most modern vehicles, you’ll need to rotate a spring-loaded tensioner away from the belt, relieving the tension so the belt can be slipped off the pulleys (see illustration). On some models, you may need to loosen the alternator mounting bolts to relieve the belt tension.
- Disconnect the electrical connectors from the alternator (see illustration).
- Unscrew the alternator mounting bolts and remove the alternator from the engine compartment.
- Installation is the reverse of removal. Be sure to follow all procedures in your service manual regarding battery re-connection.
Most vehicles have spring-loaded tensioners that must be rotated away from the belt. Here, a ratchet is being used (a ½-inch square hole is in the tensioner). On some vehicles, you’ll need to use a wrench or socket
Remove the electrical connectors from the alternator (right arrows), then remove the mounting bolts (left arrows) (typical)