Parts for your 2007 Subaru Impreza-Alternator

2007 Subaru Impreza Alternator

Based on technical sources including the Subaru Factory Service Manual (2007MY Impreza, Charging System section), Subaru Technical Information System documentation, and the Haynes Repair Manual for Subaru Impreza 2002–2011 (Electrical/Charging chapters), the 2007 Subaru Impreza is equipped with a belt-driven alternator (typically Denso or Mitsubishi Electric, around 90–110 A depending on engine/trim). So yes—the alternator is absolutely relevant and fitted to this vehicle.

The alternator on a 2007 Subaru Impreza keeps the battery topped up and powers the car’s electrics while the engine’s running—headlights, wipers, heater fan, ABS, ECU, stereo, and the lot. Its internal regulator holds charging voltage around the mid-14s so the battery charges without being overcooked. When things go south, drivers may see the battery warning light, get dim lights at idle, hear a bearing whine, or cop a flat battery after short trips.

Good servicing under the bonnet helps the alternator live a long life. A quick look during regular services (every 10,000–15,000 kilometres is a fair rhythm in AU/NZ conditions) goes a long way:

• Check the drive belt for cracks, glazing, or fraying, and set tension to spec. A slipping belt can mimic a “dead alternator.”
• Inspect the alternator plug and main output cable for corrosion or looseness, confirm the engine earth strap is clean and tight.
• With a multimeter across the battery, look for about 13.8–14.6 V at warm idle with lights and fan on. Anything well outside that range needs a closer look.
• Keep the battery healthy, a failing battery makes the alternator work overtime.

When replacement time comes, it’s a straightforward driveway job for a confident DIYer, but follow the book. Disconnect the negative battery terminal, relieve belt tension, remove the belt, undo the mounting bolts, and label the wiring before swapping the unit. Fit a quality new or reman alternator built to Subaru/Denso spec, torque the hardware to service data, and refit/retension the belt. After the first few drives (100–200 km), recheck belt tension. If the belt shows its age, replace it together with any tired idler or tensioner. On start-up, confirm the battery light goes out and voltage sits in the mid-14s. For cars running extra lights or a hefty audio setup, consider a high-quality unit with output capacity to match the load.

As always, if any doubt pops up—charging voltage oddities, hot belts, or mystery warning lights—it’s worth getting a qualified auto sparky to test the system properly, including diode ripple and load tests.

Popular questions

What voltage should a 2007 Subaru Impreza alternator produce?
At warm idle with the engine running, expect roughly 13.8–14.6 volts measured across the battery, and similar under light electrical load (headlights and fan on). If it’s much lower, the alternator, belt, wiring, or battery could be at fault, if it’s much higher, the regulator may be misbehaving.

How long does an alternator typically last on a 2007 Impreza?
It varies with use, heat, and battery condition, but many see 150,000–250,000 km. Lots of short trips, a weak battery, or high accessory loads can shorten life. Regular belt and connection checks help push it towards the higher end.

Can a weak battery damage the alternator?
Yes, a battery that won’t hold charge forces the alternator to work harder for longer, which can overheat diodes and bearings. If the battery tests poor, replace it promptly to spare the alternator.