Subaru Forester Exhaust System: Specs, Fitment & Common Faults

A genuinely alarming, honest account: a catalytic converter replaced four times under warranty on the same car, with the same code returning each time, because the root cause was never actually diagnosed — just the symptom repeatedly swapped.

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OEM Part Numbers

Accuracy note: genuinely worth knowing: diesel Foresters with a Diesel Particulate Filter (DPF) require the DPF to be replaced or professionally cleaned as part of any exhaust work involving that section — a generic universal exhaust section without matching DPF specifications can cause the car to fail its next MOT even if it drives fine.

Left-bank exhaust manifold with catalytic converter	Subaru's horizontally-opposed "boxer" engine genuinely has two separate cylinder banks, each with its own manifold and catalytic converter — this is a distinctly different physical layout from an inline engine's single manifold, and the left and right units are not interchangeable
Right-bank exhaust manifold with catalytic converter	A genuinely separate part from the left-bank unit above — both banks feed into the shared downstream system, but each has its own dedicated cat
Centre/intermediate pipe	The section where both cylinder banks' exhaust streams merge into a single pipe, genuinely separate from the twin front manifolds and the rear silencer
Rear silencer	Confirm your exact engine and trim, since Subaru used multiple distinct rear silencer references across most model generations — Symmetrical All-Wheel Drive is standard across nearly the whole range, so there's no separate FWD-specific silencer to worry about on most models

The Part That Announces Its Own Problems

Unlike a lot of the parts on this site, this is one where you'll usually hear the fault before you see it — a rattle, a drone, a sudden increase in noise that wasn't there last week. That's actually useful, since it gives you a head start on catching problems early.

Before you buy: exhaust configuration differs significantly by engine size, fuel type and whether your car has a particulate filter. Always confirm against your VIN before ordering.

What It Does

The exhaust system channels burnt gases away from the engine, reduces noise through the silencer, and on most modern cars, treats emissions through a catalytic converter and particulate filter before gases exit the tailpipe. Petrol and diesel versions of the same model often use entirely different systems due to different emissions treatment requirements.

Subaru Forester Exhaust System reference plate

A Genuinely Alarming, Honest Real Account Worth Knowing — Subaru Forester Exhaust System

If you're facing a recurring P0420 code and catalytic converter replacement, this is genuinely worth knowing before agreeing to another straight swap: one documented case on a 2017 Forester saw the catalytic converter replaced under warranty four separate times, roughly every four months, with the exact same code returning each time — because the underlying root cause was never actually diagnosed, only the symptom repeatedly swapped out. It's genuinely worth knowing that replacing a catalytic converter without first identifying and fixing whatever actually damaged it — commonly a poor battery or earth connection, a vacuum leak, a separate exhaust leak, or a faulty sensor giving the engine incorrect feedback — will very likely just result in the replacement failing again in exactly the same way.

A genuinely important diagnostic principle worth insisting on: if a dealer or garage is proposing to replace the catalytic converter for a P0420 code, it's genuinely worth asking directly what's been done to identify and rule out these other potential causes first, rather than accepting a straight swap as the default first step. A converter replaced without addressing the actual underlying cause is a genuine, documented recipe for the same fault returning within months.

It's also genuinely worth knowing that P0420 doesn't automatically mean the catalytic converter itself has failed — the code specifically relates to catalyst efficiency falling below an expected threshold, which can be triggered by several of the causes above without the converter itself being physically damaged at all.

Warning Signs, DIY Difficulty & Aftermarket Advice

These are the same regardless of make or model — see our full Exhaust System Guide for warning signs and fault codes to watch for, confirming fitment against your VIN, and which aftermarket brands are worth trusting.

More Subaru Exhaust System

The same part, covered across other Subaru models.

Subaru Forester Exhaust System: Specs, Fitment & Common Faults

OEM Part Numbers

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A Genuinely Alarming, Honest Real Account Worth Knowing — Subaru Forester Exhaust System