Quick answer: Alternator on a 2015–2019 Subaru Outback is rated Advanced and takes about 1–1.5 hours. You'll need 7 tools for this job, and parts cost about $140. This guide walks you through the full job step by step, including the mistakes to avoid.
| Part Name |
Part Number |
Price |
Buy |
| Alternator (amperage match) |
— |
$140.00 |
|
About prices: shown prices are typical retail averages and change frequently; cheaper alternatives may be available. Confirm the current price before buying.
💡 Pro tip: Order all parts at once to save on shipping
Step-by-Step Instructions
Follow these steps carefully
1
Confirm the alternator is the problem, not the battery or belt
With the engine running, expect roughly 13.5–14.5 volts at the battery terminals. Also inspect the serpentine belt and tensioner: the good news on the FB25 engine is that the alternator sits right at the top of the engine bay, making this one of the easier alternator swaps, with everything reachable from above.
🔧 Mechanic's note — Tom Becker
I've learned: the Outback's top-mounted alternator makes this one of the easiest swaps out there — everything's reachable from above. But load-test the battery first anyway; a dying battery mimics alternator failure almost exactly, and it's the cheaper fix.
2
Disconnect the battery negative terminal first
Open the hood and find the battery at the front-left of the engine bay. Loosen the negative clamp with a 10 mm socket, lift the cable off the post, and tuck it aside so it can't fall back on.
3
Photograph the belt routing from above
Note which pulleys are ribbed and which are smooth. While you're looking, check the belt for cracks or glazing and give the tensioner pulley a spin — roughness now means a cheap part to replace while access is open.
4
Release the belt tensioner and slip the belt off the alternator
Put a 15 mm socket on the belt tensioner's hex and rotate it to relieve tension, keeping fingers clear of the belt path. While holding it back, slip the belt off the alternator pulley and tuck it aside — there's no need to remove the whole belt from the car. Let the tensioner return to rest slowly; a snapped-back tensioner can crack its pulley or pinch your hand. Because the alternator sits at the top of the FB25, you get full visibility for this step — use it to double-check your routing photo.
5
Unplug the regulator connector and remove the B+ cable
With the battery disconnected, find the small regulator plug on the back of the alternator, press its locking tab, and slide it straight off — grip the connector body, not the wires. Then remove the 10 mm nut holding the heavy B+ cable to its stud and lift the cable off. Lay both connections aside where they can't touch metal. These connectors see a lot of heat cycling on the boxer engine, so if the plug feels stuck, wiggle it gently side to side rather than forcing it and snapping the latch.
6
Remove the mounting bolts and lift the alternator straight out
Back out the alternator's mounting bolts with 12 mm and 14 mm sockets, supporting the unit with your free hand as the last one comes free. A bench comparison now is your cheapest chance to catch a wrong part before it's bolted in.
7
Reinstall, re-belt, reconnect, and verify charging
Lower the new alternator into place, start every mounting bolt by hand to avoid cross-threading, then tighten them snug per the service manual — do not overtighten. Reconnect the regulator plug until it clicks and refit the B+ cable with its 10 mm nut. Route the serpentine belt exactly like your photo, confirming it sits in every pulley groove, then slowly release the tensioner. Reconnect the battery negative last, start the engine, and check roughly 13.5–14.5 volts at the battery with the headlights and blower on — and confirm the charging warning light stays off after a short drive.
🔧 Mechanic's note — Ray Delgado
I always verify charging with the headlights and blower on — 13.5–14.5 volts under load is the real test. An alternator that reads fine at idle but sags under load is on its way out.
All Done!
Test your repair before closing everything up. If something doesn't work right, double-check your steps.
⚠️ Common Mistakes to Avoid
- • Condemning the alternator without load-testing the battery first — dead batteries mimic alternator failure exactly.
- • Yanking the heat-cycled regulator connector by its wires and snapping the latch.
- • Skipping the belt-routing photo on such an easy job and mis-seating a groove anyway.
- • Leaving the B+ nut loose, which causes intermittent charging and arcing at the stud.
