Parts for your 2012 Subaru Impreza-Alternator

2012 Subaru Impreza alternator — purpose, care, and replacement tips

Technical sources confirm the 2012 Subaru Impreza is fitted with an alternator. The Subaru Workshop Manual (2012 Impreza, Electrical — Charging System), Subaru Technical Information System (STIS), and the Subaru parts catalogue (Alternator Assy, PNC 23700 for FB20-powered models) all list and detail a belt-driven alternator, making the alternator fully relevant to this vehicle.

On a 2012 Subaru Impreza, the alternator’s job is to turn engine rotation into electrical power, keeping the battery charged and running everything from the ECU and ignition to headlights, demister, and accessories. Once the engine’s under way, the alternator takes over from the battery as the main power source. This model uses an internally regulated, ECU-managed charging system with a battery current sensor, so voltage can float a little depending on load and temperature — that’s normal.

As part of regular servicing, it pays to give the charging system a once-over. A quick multimeter check across the battery with the engine running should typically show around 13.8–14.6 V, though short dips or rises can occur with smart charging. If the battery light flickers, lights dim at idle, or there’s a whining or grinding under the bonnet, it’s time for a closer look.

• Inspect the drive (serpentine) belt for cracks, glazing, or fraying, and make sure the tensioner runs smoothly. Replacing a tired belt early can save the alternator from overwork.
• Test the battery and clean the terminals. A weak battery makes the alternator work overtime and can shorten its life.
• Listen for bearing noise and check for wobble at the pulley. Any rumble usually means the bearings are on the way out.
• Keep splash shields intact, water and grit are enemies of the alternator’s bearings and electronics.

When replacement is due, match the amperage rating and plug type to the original. Quality OEM or reputable reman units (commonly Denso/Hitachi on these cars) tend to be quieter and last longer. Disconnect the negative battery terminal before starting, follow the workshop manual for bolt torques and belt routing, and consider fitting a new belt while you’re there. Most workshops will sort the swap in about 1–2 hours. Avoid reverse-polarity jump starts — that can cook the rectifier in a heartbeat. With sensible checks at each service and prompt attention to warning signs, the Impreza’s alternator will usually go the distance for many kilometres.

Popular questions about a 2012 Subaru Impreza alternator

What voltage should I see from the alternator?
With the engine running, most owners will see roughly 13.8–14.6 V at the battery. Because this model uses ECU-controlled charging, it may vary slightly with load, temperature, and battery state — brief readings a bit lower or higher can be normal. If it’s sitting near battery voltage (around 12.3 V) with the engine on, charging is likely not happening.

How long do these alternators typically last?
It’s common to see 150,000–250,000 km from an original unit if the belt and battery are kept in good nick. Signs it’s time include a steady battery light, dim lights, whining or grinding from the alternator, or repeated flat-battery dramas despite a healthy battery.

Can I keep driving with the battery light on?
It’s risky. Once the battery’s depleted, the engine can stall and power steering, ABS, and lights can drop out. If the light comes on, switch off non-essential electrical loads and head to a workshop or home base promptly for testing.