🔧 Impreza - Alternator Replacement

The alternator charges your battery and powers the electrical system while the engine runs. On your Impreza, it sits at the front/top of the engine and can be replaced from above by removing the belt and a few bolts and connectors.

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

Assumption: Stock 2.0L layout with OEM-style alternator and belt tensioner.

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⚠️ Safety & Precautions

• ⚠️ Disconnect the negative battery cable first to prevent a short at the alternator “B+” terminal.
• ⚠️ Keep fingers/tools clear of the belt path; the tensioner is spring-loaded.
• ⚠️ Work on a cool engine; the radiator fans can turn on unexpectedly—keep hands clear.
• ⚠️ Do not pry on the alternator wiring; damaged connectors can cause charging problems.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 10mm socket
• 12mm socket
• 14mm socket
• 10mm wrench
• 12mm wrench
• 14mm box wrench
• 3/8" ratchet
• 3/8" torque wrench (10–80 Nm range)
• 6" extension (3/8")
• Flat trim tool
• Flathead screwdriver
• Small pick tool
• Digital multimeter
• Fender cover

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Alternator assembly - Qty: 1
• Accessory drive belt - Qty: 1
• Dielectric grease - Qty: 1

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📋 Before You Begin

• 🅿️ Park on level ground, shift to Park, and set the parking brake.
• 🔑 Remove the key/fob from the car so the system stays asleep.
• 🧼 Lay a fender cover to protect paint while you lean in.
• 🔋 Plan to disconnect the battery: negative cable off first, on last.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Disconnect the battery

• Use a 10mm wrench to loosen the negative (-) battery terminal clamp and remove it from the post.
• Tuck the cable end aside so it cannot spring back onto the battery.

Step 2: Remove the front air duct/snorkel (access)

• Use a flat trim tool to pop up any plastic clips holding the duct in place.
• Use a flathead screwdriver to loosen any band clamp(s) (if equipped), then lift the duct out.
• This opens space to lift the alternator out.

Step 3: Relieve belt tension and remove the belt

• Locate the belt tensioner near the front of the engine (spring-loaded arm with a hex/bolt head).
• Use a 14mm box wrench (or 14mm socket with 3/8" ratchet) on the tensioner hex and rotate to relieve tension.
• While holding tension off, slip the belt off the alternator pulley and then remove the belt from the other pulleys.
• Take a quick photo of the belt routing.

Step 4: Disconnect alternator electrical connectors

• Unplug the small regulator connector: use a small pick tool to gently lift the lock tab (a lock tab is a small plastic catch that must be released) and pull the connector straight off.
• Remove the rubber boot from the alternator “B+” terminal.
• Use a 10mm socket with 3/8" ratchet to remove the B+ retaining nut, then lift the ring terminal off and move the cable aside.
• Do not let the B+ cable touch metal.

Step 5: Unbolt and remove the alternator

• Use a 12mm socket and 3/8" ratchet to remove the alternator mounting bolts (upper and lower, depending on bracket layout).
• If the alternator is stuck in the bracket, use a flathead screwdriver carefully at the bracket ear to wiggle it free (do not pry on the aluminum housing hard).
• Lift the alternator up and out of the engine bay.

Step 6: Install the new alternator

• Set the new alternator into place and hand-start all mounting bolts to avoid cross-threading.
• Use a 12mm socket with 3/8" ratchet to snug the bolts evenly.
• Use a 3/8" torque wrench to tighten mounting bolts: Torque to 39 Nm (29 ft-lbs).

Step 7: Reconnect alternator wiring

• Apply a thin film of dielectric grease to the small connector seal (not the metal pins).
• Install the B+ ring terminal onto the stud, then use a 10mm socket with 3/8" torque wrench: Torque to 9 Nm (80 in-lbs).
• Reinstall the rubber boot over the B+ terminal.
• Plug in the regulator connector until it clicks.

Step 8: Reinstall the belt

• Route the belt around all pulleys except the alternator pulley (use your photo as a reference).
• Use a 14mm box wrench on the tensioner to relieve tension, then slip the belt onto the alternator pulley.
• Slowly release the tensioner and visually confirm the belt is seated fully in every pulley groove.

Step 9: Reinstall the air duct/snorkel

• Reinstall the duct and any clips you removed using a flat trim tool.
• Re-tighten any clamp(s) using a flathead screwdriver.

Step 10: Reconnect the battery

• Install the negative (-) battery cable and tighten using a 10mm wrench until snug.

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✅ After Repair

• 🔎 Start the engine and listen for belt squeal or slapping; shut off and re-check belt seating if you hear noise.
• 📏 Use a digital multimeter at the battery posts: engine running should typically show about 13.8–14.7V.
• 💡 Confirm the battery/charging warning light stays off on the dash.
• 🧯 Recheck the B+ boot is fully covering the terminal.

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💰 DIY vs Shop Cost

Shop Cost: $550-$950 (parts + labor)

DIY Cost: $220-$520 (parts only)

You Save: $330-$430 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.5-2.5 hours.

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🎯 Ready to get started?

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