🔧 Impreza - Alternator Replacement

The alternator charges your battery and powers the electrical system while the engine runs. Replacing it on your Impreza is mostly about getting safe access, removing the drive belt, unplugging the wiring, and swapping the alternator.

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

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⚠️ Safety & Precautions

• ⚡ Disconnect the negative battery terminal first to prevent a short.
• 🔥 Work on a cool engine; the exhaust and radiator area can burn you.
• 🧤 Keep hands clear of the belt path; pinch hazard when releasing the tensioner.
• 🛑 Never let the alternator B+ cable touch metal; it can arc.

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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 (10–100 Nm range)
• 3" extension (3/8")
• Flathead screwdriver
• Trim clip removal tool
• Serpentine belt tool (specialty)
• 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 Recommended if belt is worn
• Dielectric grease - Qty: 1

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📋 Before You Begin

• Park on level ground, shift to Park, and set the parking brake.
• Open the hood and let the engine cool completely.
• Disconnect the battery: use a 10mm socket to remove the negative (–) terminal and isolate it so it can’t spring back.
• Take a quick photo of the belt routing.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the intake ducting for access

• Loosen the air duct clamps with a flathead screwdriver (or a 10mm socket, depending on clamp style).
• Remove any plastic clips with a trim clip removal tool.
• Lift the intake snorkel/ducting out of the way so you can clearly reach the alternator and belt area.

Step 2: Release belt tension and remove the drive belt

• Place a 14mm socket on the belt tensioner hex and rotate to relieve tension (use a serpentine belt tool (specialty) if you need extra leverage).
• Slide the belt off the alternator pulley while holding the tensioner released.
• Slowly let the tensioner return to its resting position.
• Don’t let the tensioner snap back.

Step 3: Disconnect alternator electrical connections

• Remove the protective rubber boot on the alternator B+ terminal by hand.
• Remove the B+ cable nut using a 10mm socket (some units may use 12mm socket).
• Unplug the alternator electrical connector by pressing the lock tab and pulling straight out.
• Add a tiny amount of dielectric grease to the connector seal before reinstalling (optional but helpful).

Step 4: Remove the alternator mounting bolts

• Remove the alternator mounting bolts using a 12mm socket and/or 14mm socket with a 3" extension (3/8") and 3/8" ratchet.
• Support the alternator with one hand as the last bolt comes out so it doesn’t drop.
• Lift the alternator out of the engine bay.
• Torque note: Alternator bracket/mounting bolt torque varies by fastener location. Torque to Subaru factory specification (FSM) using a 3/8" torque wrench.

Step 5: Install the new alternator

• Set the new alternator into position and start all mounting bolts by hand to avoid cross-threading.
• Tighten mounting bolts evenly using a 12mm socket/14mm socket, then final tighten with a 3/8" torque wrench.
• Torque to Subaru factory specification (FSM).

Step 6: Reconnect alternator wiring

• Reconnect the alternator electrical connector until it clicks (no tool needed).
• Install the B+ cable and nut using a 10mm socket (or 12mm socket if equipped).
• Torque to Subaru factory specification (FSM), then reinstall the rubber boot fully over the terminal.

Step 7: Reinstall the drive belt

• Route the belt exactly like your photo (or the under-hood routing diagram if present).
• Rotate the tensioner with a 14mm socket (and serpentine belt tool (specialty) if needed), slip the belt onto the alternator pulley, then slowly release the tensioner.
• Visually confirm the belt sits in the grooves on every pulley.

Step 8: Reinstall intake ducting

• Reinstall the intake ducting and clips using a trim clip removal tool as needed.
• Tighten hose clamps using a flathead screwdriver (or 10mm socket).

Step 9: Reconnect the battery

• Reconnect the negative battery terminal using a 10mm socket.
• Torque to Subaru factory specification (FSM).

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✅ After Repair

• Start the engine and listen for belt squeal or slapping noises.
• With the engine idling, check charging voltage at the battery using a digital multimeter: you should typically see about 13.8–14.7V.
• Turn on headlights and blower motor; verify voltage stays stable and the battery light stays off.
• Recheck belt alignment after a short test drive.

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💰 DIY vs Shop Cost

Shop Cost: $450-$900 (parts + labor)

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

You Save: $270-$450 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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