How to Change an Alternator in a GMC Sonomaby Grace Mclain
The alternator replacement process on the GMC Sonoma pickup is basically the same for all models. The alternator regulates the vehicle's charging system. The alternator also keeps the battery fully charged and it keeps the complete electrical system up and running. When the alternator fails, it will stop charging the battery and the battery will die. Once the battery dies, the vehicle's electrical system will fully shut down.
Open the Sonoma's hood and locate the battery. Remove the negative battery cable from the battery with an adjustable wrench. The negative battery cable will be attached to the negative battery post, which has a minus (-) symbol embossed near or on the post. Secure the negative battery cable to the side so that it does not touch metal and cannot inadvertently slide into contact with the battery post.
Locate the alternator and the serpentine belt tensioner on the front of the engine. The alternator on the GMC Sonoma is located on the passenger side. Relieve the tension on the belt tensioner with a ratchet and a 13mm socket. Turn the tensioner counterclockwise and remove the belt from the alternator pulley only.
Remove the 13mm nut on the backside of the alternator. This nut is holding the wire connector to the rear of the alternator. Then pull the wire off the stud and lay it out of the way. Then pull the electrical plug out of the back of the alternator and lay it out of the way.
Remove the two main bolts holding the alternator to the alternator bracket. One bolt is through the top left-hand side of the alternator and the other bolt is through the bottom of the alternator in the center. Remove these bolts with a 13mm socket and ratchet. Turn the bolts counterclockwise to loosen and remove them from the alternator. Then slide the alternator out of the alternator bracket. Set the alternator aside.
Slide the new alternator into the bracket and slide the lower bolt in first. Then slide the top left-hand-side bolt in. Tighten the bolts down to the proper bolt torque settings. The proper torque settings for the alternator bolts on the GMC Sonoma series is 32 foot-pounds as recommended by the Haynes Repair Manual. You can use a torque wrench and a socket to get the proper torque settings. Once the alternator bolts are tight, plug the wire connector back in to the lower plug socket on the rear of the alternator. Also reattach the wire connector to the center stud and screw the 13mm nut back down tight over the wire connector.
Relieve the tension on the belt tensioner and slide the serpentine belt back over the alternator pulley. Release the belt tensioner and let it pull the slack out of the belt and bring the belt back to the proper tension.
Reconnect the negative battery cable to the battery post and tighten the cable bolt back down tight with the adjustable wrench.
Crank the Sonoma and let the new alternator charge the battery. Make sure the serpentine belt is running evenly and securely inside the alternator pulley. Turn the engine off after 20 to 30 minutes and close the hood.
- You can purchase a small torque wrench at most auto parts stores. The reason for having the proper torque on the alternator bolts is so that you do not over-tighten the bolts and crack or break the alternator bracket.
- Always wear safety glasses when working around the battery.
Items you will need
- Adjustable wrench
- Small torque wrench
- New alternator
- "Haynes Repair Manual; 1992-1994; 1995-2006 GMC Sonoma Trucks"; John Haynes; 2007
- Pictures of a GMC Sonoma Alternator With Bolt Positioning
- Photodisc/Photodisc/Getty Images