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.
Illustration for editorial purposes
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OEM Part Number: confirm via VIN — Rear silencer (aftermarket) Bosal 229-683
| Rear silencer (back box) — aftermarket | Bosal 229-683; Vegaz SAS-56, SAS-56IMA, SAS-55/55IMA (left rear), SAS-44, SAS-43IMA, SAS-60 (581 mm), SAS-63 (right rear), SAS-18, SAS-5; Polmo 46.21, 46.22, 46.23, 46.10; Izawit 45.006, 45.008 (left rear); (also Imasaf 68.44.57, 68.22.07, 68.44.67) |
|---|---|
| Centre / intermediate silencer — aftermarket | No branded centre silencer is listed for this car in UK catalogues — order the centre section against your VIN |
| Front pipe / catalytic converter (DPF on diesels) — aftermarket | or DPF: Bosal 090-640 (Euro 3); Walker 28249 (740 mm, code 92), 28747 (450 mm, code 91); Ernst 759717 (Euro 1/2), 757997 (Euro 3/4, 880 mm); Vegaz SAK-909, SAK-913, SAK-925; BM Catalysts BM91070H, BM91976H, BM80563H; JMJ 1091581 (EJ20/EJ201/EJ251), 1090122, 1091686 |
| Genuine (OE) numbers quoted | None quoted in catalogue listings — order genuine parts against your VIN |
| Fitment notes | Petrol, one diesel (2.0D SJD) and bi-fuel; left/right/centre positions differ. |
Subaru Forester Exhaust System: The Part That Announces Its Own Problems
On the Subaru Forester, most faults are things you'd spot visually first, but this one usually announces itself acoustically — a rattle, a drone, a noticeable jump in noise levels. That's actually helpful, since it means you'll likely notice trouble well before it gets serious.
Subaru Forester Exhaust System: What It Does
Three jobs happen inside the Subaru Forester's exhaust system: routing burnt gases away from the engine, quieting them through the silencer, and treating emissions via a catalytic converter and particulate filter. Petrol and diesel variants often need completely different systems to meet their respective emissions requirements.
Subaru Forester Exhaust System: Watch: Replacing It
Straight muffler replacement on an SJ; best match in the batch
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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.
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.
Subaru Forester Exhaust System: 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.