Parts for your 2012 Subaru Impreza-Ignition coils

2012 Subaru Impreza ignition coils — what they do and when to replace them

Based on technical sources including the Subaru Factory Service Manual for the 2012MY Impreza (FB-series engine, Ignition System), Subaru’s Technical Information System (STIS), and the Subaru electronic parts catalogue and major ignition manufacturers’ application guides, the 2012 Subaru Impreza petrol models are fitted with individual coil-on-plug ignition coils. So yes, ignition coils are used and are absolutely relevant on this vehicle.

On the 2012 Impreza, each cylinder gets its own coil mounted directly on the spark plug. The engine control unit triggers each coil to step up the 12-volt battery supply into a high-voltage spark at precisely the right moment. That coil-on-plug layout improves spark energy, cuts losses from old-school leads, and helps the car run cleaner and more efficiently.

Ignition coils aren’t a scheduled “consumable” like filters or brake pads, but they do benefit from periodic checks during servicing, especially when spark plugs are changed. A technician should inspect connectors and wiring for heat damage, make sure the coil boots are clean and dry, and confirm there’s no oil in the plug tubes (which can come from a rocker cover gasket leak). If the check engine light’s on, scan for misfire codes (P0301–P0304) or coil circuit faults (P0351–P0354) and test the suspect coil before replacing.

• Signs a coil may be failing: rough idle, hesitation under load, hard starting, higher fuel use, or a flashing check engine light.
• Physical red flags: cracked housings, green/white corrosion on terminals, or carbon tracking on the boot.

Replacement is straightforward for a competent home spanner-spinner: disconnect the battery, unplug the coil, remove the hold-down bolt, and lift the coil straight off the plug. Fit quality OEM-equivalent coils (commonly Denso for Subaru), seat the boot firmly, use a dab of dielectric grease on the insulator (not the terminal), and tighten the fastener to the factory spec — no overdoing it. After refitting, clear fault codes and take a proper test drive. Many owners swap just the faulty coil, on higher-kilometre cars or where heat has taken a toll, doing them as a set can save repeat visits.

With good plugs and clean, dry plug wells, coils can easily run well past 150,000 km. Avoid pressure-washing under the bonnet, and fix any oil or coolant leaks that could contaminate the coil boots to keep the system happy.

How long do ignition coils last on a 2012 Subaru Impreza?

With healthy plugs and no oil or moisture in the plug tubes, coils commonly last well beyond 150,000 km. There’s no fixed replacement interval in Subaru’s service schedules, they’re replaced on condition. If misfires start appearing under load or when hot, test the coils before they become a roadside headache.

What are the classic symptoms of a bad coil on this model?

Expect a lumpy idle, hesitation climbing hills, poorer fuel economy, and a check engine light. Scans often show cylinder-specific misfire codes (P0301–P0304). Visual clues include cracked coil bodies, corrosion on terminals, or carbon tracking down the boot.

Is it worth replacing all four coils at once?

If only one coil has failed on a modest-kilometre car, replacing the single unit is fine. On higher-kilometre engines or if multiple misfires have occurred over a short time, replacing the full set can be cost-effective, especially if heat or oil contamination has aged the others.