🔧 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 of the engine and is driven by the serpentine belt, so the job is mainly belt removal, unbolting the alternator, then reinstalling and tensioning correctly.

Difficulty Level: Intermediate | Estimated Time: 1.0-2.0 hours

Assumption: Stock FB20 2.0L layout; torque values are best-effort OEM-typical where exact spec varies by fastener.

---

⚠️ Safety & Precautions

• ⚠️ Disconnect the negative battery cable first to prevent a short.
• ⚠️ Let the engine cool; the exhaust and radiator area can burn you.
• ⚠️ Keep fingers and tools clear of the belt path.
• ⚠️ Do not pry on the alternator case or electrical studs.

---

🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 12mm socket
• 14mm socket
• 3/8" ratchet
• 3/8" torque wrench (10–80 Nm range)
• 3/8" breaker bar
• 6" socket extension
• Serpentine belt tool (specialty)
• Flat trim tool
• Needle-nose pliers
• Work light
• Nitrile gloves
• Safety glasses

---

🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Alternator - Qty: 1
• Serpentine belt - Qty: 1
• Dielectric grease - Qty: 1

---

📋 Before You Begin

• Park on level ground, set the parking brake, and put the shifter in neutral.
• Open the hood and remove the key from the area.
• Disconnect the battery: use a 10mm socket to remove the negative (–) terminal first, and tuck it aside so it can’t spring back.
• Take a quick photo of the belt routing (or draw a simple sketch).

---

🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the air intake snorkel (if it blocks access)

• Use a flat trim tool to pop out any plastic clips.
• Use a 10mm socket to remove any bolts, then lift the snorkel out.

Step 2: Relieve belt tension and remove the serpentine belt

• Locate the automatic belt tensioner (spring-loaded pulley).
• Use a serpentine belt tool (specialty) or 14mm socket with a breaker bar to rotate the tensioner and relieve tension.
• Slide the belt off the alternator pulley first, then remove the belt from the rest of the pulleys.
• Tip: Keep the belt routing photo visible.

Step 3: Disconnect the alternator electrical connections

• Unplug the alternator connector by pressing the lock tab and pulling straight back (don’t yank the wires). Use needle-nose pliers only if needed.
• Remove the main power cable nut: pull back the rubber boot, then use a 12mm socket to remove the nut from the charging stud.
• Move the cable aside so it can’t touch metal.
• Apply a thin film of dielectric grease to the connector seal during reassembly.

Step 4: Unbolt the alternator

• Support the alternator with one hand.
• Use a 14mm socket with a ratchet and extension to remove the alternator mounting bolts (typically an upper and lower bolt).
• If it feels “stuck” in the bracket, gently wiggle it out by hand. Do not pry on the aluminum housing.

Step 5: Install the new alternator

• Set the new alternator into the bracket and hand-start all mounting bolts to avoid cross-threading.
• Use a 14mm socket to snug the bolts evenly.
• Torque the alternator mounting bolts with a torque wrench: Torque to 35–45 Nm (26–33 ft-lbs).

Step 6: Reconnect alternator wiring

• Install the main power cable onto the charging stud and start the nut by hand.
• Use a 12mm socket to tighten the nut: Torque to 9–12 Nm (80–106 in-lbs).
• Reinstall the rubber boot fully over the stud.
• Plug in the alternator connector until it clicks.

Step 7: Reinstall the serpentine belt

• Route the belt around all pulleys except the alternator pulley last (use your photo/diagram).
• Use the serpentine belt tool (specialty) or 14mm socket with a breaker bar to rotate the tensioner.
• Slip the belt onto the alternator pulley, then slowly release the tensioner.
• Visually check the belt is fully seated in every pulley groove.

Step 8: Reinstall intake snorkel and reconnect battery

• Reinstall the snorkel using the 10mm socket and any clips with the flat trim tool.
• Reconnect the battery negative terminal using a 10mm socket (snug, do not over-tighten).

---

✅ After Repair

• Start the engine and confirm the battery/charging warning light turns off.
• Listen for belt squeal or slapping; if present, shut off and re-check belt seating.
• With the engine idling, a healthy charging system is typically about 13.5–14.7V at the battery using a multimeter.
• Recheck for loose tools, and make sure the alternator wiring boot is covering the stud.

---

💰 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 1.0-1.8 hours.

---

🎯 Ready to get started?

HowToo makes it easy: same-day/2-day shipping on every part, plus all the tools and specialty tools you need! Check out the parts and tools sections below to add everything to your cart.