1999-2007 GMC Sierra Alternator Replacement

This guide will demonstrate how to replace an...

iFixit Library 1999-2007 GMC Sierra Moderate 30 minutes - 1 hour Guide 137526

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Guide overview

Before you begin

This guide will demonstrate how to replace an alternator in any GMC Sierra made from 1999 to 2007. Although the guide will be demonstrated on my 1999 Sierra, you can use the same procedure for any GM truck or SUV that uses a Vortec V8 engine.

Step 1

Repair step

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Using an 8mm wrench, disconnect the negative battery terminal. This is the one on the right (closest to the engine).
Caution: Hazardous situation which, if not avoided, could result in minor or moderate injury.

Step 2

Repair step

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Loosen the hose clamps on the factory intake tube with an 8mm socket and remove the intake tube. One hose clamp will be located at the port of the intake manifold and one will be near the factory air box.

Step 3

Repair step

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Remove the black wire from the back of the alternator using a 10mm socket and disconnect the voltage sensor. For the Voltage sensor, depress the tab towards the base of the sensor and pull outwards.

Step 4

Repair step

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Using a 15mm socket on a half inch socket wrench, loosen the belt tensioner by pushing downwards. The tensioner is spring loaded so you will need to use your free hand to remove the serpentine belt.

Step 5

Repair step

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TOOL USED ON THIS STEP Battery Charger Referenced by the iFixit guide

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Using a 16mm socket, remove both alternator mounting bolts and remove the alternator. These will be located at the base of the alternator. You may need a crowbar to remove the alternator from the mounting bracket because the mounting points often rust.
After replacing the alternator, make sure the battery is fully charged before starting the vehicle. You can do this by using a battery charger. Connect the red (positive) lead to the red (positive) battery terminal. Then do the same for the negative lead and terminal (black).
Set the charger to 12V and TRICKLE CHARGE, then wait until the indicator reads FULL CHARGE.