How to Change an Alternator on a Chevy 5.3 Liter Vortec V8 Engine

Your Chevy Avalanche 1500’s alternator is an integral part of starting and running your vehicle. Your truck’s alternator charges the battery to help start your truck, and provides power to your truck’s electrical accessories while the engine is running, which includes power windows, radio, windshield wipers, and more. When the alternator fails, your Chevy’s electrical systems will only stay on until the battery's reserve charge is depleted. Your truck may die, but you might be able to restart it with a jump start. Replacing a worn or failing alternator on your 2003 Chevy Vortec 5.3-liter V8 engine is a straightforward repair that can help ensure your truck’s electrical system is performing properly. If you need to replace your truck’s alternator, you may notice dim headlights or that your battery is not staying fully charged. Our step-by-step instructions will help you perform an alternator replacement on your Chevy Avalanche.


Tools & Materials List

Remove the Old Alternator

Install the New Alternator

Tools & Materials

Safety Eye Glasses Safety Glasses

Protective Gloves Nitrile Gloves

Drain Pan Drain Pan

ratchet Ratchet

Sockets Sockets

fan clutch wrench Fan Clutch Wrench

Alternator Alternator

Step-by-Step Instructions to Change Your Alternator

Today, we’ll be installing an alternator on this 2003 Chevy Avalanche 1500, but this process will be similar on a lot of Chevy Vortec V8s. A good number of GM and Chevy trucks were equipped with this engine, but be sure to know the specifics for your truck before getting started. And if you’re not completely comfortable doing this yourself, we’d be happy to recommend a professional technician in your area.

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Remove the Old Alternator

Man in blue gloves holding negative cable by car battery

Step 1: Disconnect the Negative Battery Cable

Before you start to remove your alternator, park on a level surface and open your hood. Disconnect your negative battery cable and move it aside someplace safe.


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Mechanic removing Vortec V8 engine cover

Step 2: Remove the Vortec V8 Engine Cover

Take off the engine cover by loosening the intake manifold sight shield bolt and lifting the cover out from the vehicle. After removing the Vortec V8 engine cover, remove the engine cover retainer, if required.
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Man holding an air cleaner outlet duct

Step 3: Remove the Air Cleaner Outlet Duct

Then, loosen the air cleaner outlet duct clamps at the throttle body and mass airflow/intake temperature sensor. Remove the radiator inlet hose clip from the outlet duct and then remove the air cleaner outlet duct.
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Mechanic removing old serpentine belt from the engine

Step 4: Remove the Serpentine Belt

Remove the accessory drive belt by using a breaker bar with a hex-head socket on the drive belt tensioner bolt. Rotate the drive belt tensioner clockwise in order to relieve tension on the belt. Then you can remove the belt from the pulleys and tensioner. Slowly release the tension on the tensioner, then remove the breaker bar and socket.



Do It Right: Clean and inspect the belt surfaces of all the pulleys.

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Man in blue gloves holding wiring harness plug

Step 5: Disconnect the Wiring Harness Plug

Disconnect the wiring harness plug from the alternator by pushing down on the tab and pulling the connector straight out. Slide down the protective boot to reveal the terminal stud.
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Step 6: Disconnect the Battery Output

Step 6: Disconnect the Battery Output

Remove the battery output BAT terminal nut and disconnect the battery output BAT cable.
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Mechanic removing bolts from old alternator

Step 7: Remove Mounting Bolts

Remove both mounting bolts from the old alternator.
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Man holding old alternator above the engine

Step 8: Remove the Old Alternator

You should now be able to remove the old alternator by gripping it firmly and pulling it away from the engine.
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Install the New Alternator

New Ultima alternator in position for install

Step 9: Position the New Alternator

Put the new alternator in place and prepare for installation.
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Man in blue gloves torqueing the bolts to secure a new alternator

Step 10: Reinstall the Mounting Bolts

Secure the new alternator with the mounting bolts you removed previously. Torque these bolts to 37 foot pounds.
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Mechanic holding battery output cable nut on the back on an alternator and then torqueing it

Step 11: Reconnect the Battery Output BAT Cable

Reconnect the battery output BAT cable and tighten the terminal nut to 13 foot pounds.
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Man plugging cable into the back of the alternator

Step 12: Reconnect the Wiring Harness Plug 

Replace the protective boot and reconnect the wiring harness plug.
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Man using hit hands to put serpentine belt onto engine pulleys

Step 13: Reinstall the Serpentine Belt

Reinstall the drive belt by routing it around all the pulleys except the idler pulley. Then use your breaker bar and socket to rotate the tensioner clockwise. Install the drive belt under the final idler pulley and slowly release tension on the belt tensioner. Remove your breaker bar and socket and inspect the belt for proper alignment.
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Mechanic in blue gloves lower engine cover back under hood of truck

Step 14: Reinstall the Air Cleaner Outlet Duct & Engine Cover

Reinstall the air cleaner outlet duct by putting it in place and torquing it to 62 inch pounds. Reinstall engine cover retainer, if required. Then, install the Vortec V8 cover and tighten the bolts to 44 inch pounds.



Do It Right: Don’t let the cover contact the manifold absolute pressure sensor wire harness connector.

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Man using ratchet to connect terminal to batter and mechanic standing in from of Chevy Avalanche

Step 15: Reconnect the Battery and Close the Hood

Reconnect your negative battery terminal and close the hood.
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Additional Resources

How to Replace a Camshaft Position Sensor

How to Replace a Camshaft Position Sensor
Shop Oil

Selecting the Right Motor Oil for Your Engine
How to Check/Set Gap/Replace Spark Plugs

How to Check, Set Gap & Replace Spark Plugs
These step-by-step instructions and video detail an alternator replacement on a 2003 Chevy Avalanche 1500, and will be similar to replacement procedures on 2004 Chevy Avalanche models, and Chevy Avalanche 2500 from 2003, 2004, 2005, and 2006. The replacement procedures will also be similar for select Chevy Silverado 1500, 2500, and 3500 models from 2004, 2005, 2006, and 2007, as well as Cadillac Escalade models from 2003, 2004, and 2005 equipped with a 5.3L Vortec engine. Replacing a damaged or faulty alternator helps you maintain a safe, functioning electrical system, and can keep your truck’s electrical accessories running smoothly and your battery charged. If you notice your truck’s headlights or dashboard lights are dim, or if your truck’s battery is not staying fully charged, you should test and replace your alternator as soon as possible to prevent stalling and inconvenient breakdowns.
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The automotive repair work depicted in this series is performed under the direction of the manufacturer of the product featured. Prior to undertaking any of the demonstrated repairs on your vehicle, we suggest you consult with a certified mechanic or another professional who can adequately advise you of the proper repair or remedy required. O’Reilly Automotive Stores, Inc. and its affiliates (“O’Reilly”) disclaims any responsibility for injury or damage resulting from a viewer’s attempt to recreate the repairs shown in this series.