🔧 WRX - Alternator Replacement

The alternator charges the battery and powers the car’s electrical system while the engine is running. On your WRX, replacement involves removing the drive belt, unplugging the alternator wiring, and swapping the alternator unit.

Difficulty Level: Intermediate | Estimated Time: 1.5-3.0 hours

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⚠️ Safety & Precautions

• Disconnect the negative battery cable before touching the alternator wiring (the main alternator wire is always “live” otherwise).
• Let the engine cool completely; the turbo/nearby parts can be very hot.
• Keep fingers and tools clear of the belt path and pulleys.
• Support any removed ducts/hoses so you don’t crack plastic fittings.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Mechanic gloves
• 10mm socket
• 12mm socket
• 14mm socket
• 3/8" ratchet
• 3/8" torque wrench
• 3" socket extension
• 6" socket extension
• 14mm box-end wrench
• Flat trim clip tool
• Pick tool
• Digital multimeter

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Alternator - Qty: 1
• Serpentine/drive belt - Qty: 1
• Dielectric grease (small packet) - Qty: 1

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📋 Before You Begin

• Park on level ground, set the parking brake, and open the hood.
• Make sure the key is out of the ignition.
• Disconnect the battery: use a 10mm socket to remove the negative (-) terminal and tuck it aside so it can’t spring back.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the intake snorkel/ducting (for access)

• Use a flat trim clip tool to pop up the plastic clips holding the snorkel/upper duct.
• Use a 10mm socket to remove any snorkel bolts (if equipped).
• Lift the snorkel/duct out and set it aside.

Step 2: Release belt tension and remove the belt from the alternator

• Locate the belt tensioner pulley.
• Use a 14mm box-end wrench on the tensioner’s hex and rotate it to relieve belt tension. Hold tensioner firmly; it’s spring-loaded.
• Slip the belt off the alternator pulley and slowly release the tensioner.
• If you’re reusing the belt, take a quick photo of the belt routing before removal.

Step 3: Disconnect alternator electrical connections

• On the back of the alternator, remove the rubber boot covering the main charge terminal.
• Use a 10mm socket to remove the nut on the main charge wire (B+ terminal) and move the cable aside safely.
• Torque to 9.8 Nm (7.2 ft-lbs) when reinstalling the B+ terminal nut.
• Unplug the alternator’s electrical connector: press the tab (use a pick tool if the tab is stubborn) and pull straight back.
• Add a tiny smear of dielectric grease to the connector seal during reassembly (optional but helpful).

Step 4: Remove alternator mounting bolts

• Use a 14mm socket, 3/8" ratchet, and a 3" or 6" extension as needed to remove the alternator mounting bolts.
• Support the alternator with one hand as you remove the last bolt so it doesn’t drop.
• Lift the alternator up and out of the engine bay.

Step 5: Install the new alternator

• Set the new alternator into place and hand-thread the mounting bolts to avoid cross-threading.
• Use a 14mm socket to snug the bolts evenly.
• Use a 3/8" torque wrench to tighten the alternator mounting bolts: Torque to 39 Nm (29 ft-lbs).

Step 6: Reconnect alternator wiring

• Plug in the alternator connector until it clicks.
• Install the main charge wire onto the B+ terminal and start the nut by hand.
• Use a 10mm socket and then a 3/8" torque wrench: Torque to 9.8 Nm (7.2 ft-lbs).
• Reinstall the rubber protective boot over the charge terminal.

Step 7: Reinstall the drive belt

• Route the belt correctly around the pulleys (use your photo).
• Use a 14mm box-end wrench to rotate the tensioner again and slip the belt fully onto the alternator pulley.
• Visually confirm the belt is seated in every pulley groove (no ribs hanging off).

Step 8: Reinstall intake snorkel/ducting

• Reinstall the snorkel/duct and align the clips/holes.
• Use a 10mm socket for any bolts and press clips in by hand.

Step 9: Reconnect the battery

• Reconnect the negative (-) battery terminal using a 10mm socket.
• Make sure the terminal is snug and doesn’t rotate by hand.

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✅ After Repair

• Start the engine and confirm there are no belt squeals or warning lights.
• Use a digital multimeter at the battery posts: engine idling should typically show about 13.5V–14.8V charging.
• Turn on headlights and rear defroster and recheck voltage; it should remain in the charging range.
• Recheck the belt seating after a short 5-10 minute drive.

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💰 DIY vs Shop Cost

Shop Cost: $450-$850 (parts + labor)

DIY Cost: $180-$450 (parts only)

You Save: $270-$400 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.5-3.0 hours.

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🎯 Ready to get started?

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