Parts for your 1999 Subaru Forester-Fuel cap

1999 Subaru Forester fuel cap — what it does, why it matters, and when to replace it

Based on Subaru’s SF-series Forester owner’s/service literature and genuine parts listings (fuel filler cap commonly catalogued as 42031FC030, with some markets noting 42031AE020), the 1999 Subaru Forester is designed to use a proper EVAP-sealing fuel cap. OBD‑II evaporative emissions diagnostics on this model rely on an airtight cap, with Subaru service guidance to tighten the cap until it clicks. So yes — a fuel cap is relevant, fitted, and essential on a 1999 Forester.

For owners and buyers, the fuel cap on a 1999 Forester isn’t just a lid for the petrol filler. It seals the tank to contain vapours, helps the evaporative emissions system run correctly, and prevents dust, water, and road grime getting into the tank. A healthy cap stops nuisance check-engine lights after refuelling and keeps that faint whiff of petrol out of the cabin and garage. The genuine-style cap is a tethered, click-to-tighten design that maintains the right seal while allowing safe pressure and vacuum relief in the tank.

As part of regular servicing, it’s worth giving the cap five minutes of attention. Wipe the rubber sealing ring and the filler neck with a clean, lint-free rag, grit here is the enemy of a good seal. When refuelling, tighten the cap until it clicks several times — that’s Subaru’s intended confirmation it’s seated. Don’t lubricate the seal with oil-based products, if anything, a quick clean is all it needs.

• Signs a cap needs replacing:
  • Fuel smell around the rear quarter or after parking.
  • Check Engine Light with small/medium EVAP leak faults (often P0440, P0442, P0456).
  • Perished, cracked, or flattened rubber seal, or a cap that won’t “click”.
• Replacement tips:
  • Choose a genuine Subaru cap or a quality aftermarket unit that’s EVAP-rated for the 1999 Forester.
  • Locking caps are fine if they’re Forester-compatible and maintain correct EVAP sealing.
  • If in doubt, match by VIN or existing part number, the wrong cap can trigger warning lights.

There’s no strict replacement interval, in Aussie and Kiwi conditions, many original caps last years, but rubber does age. If the seal looks tired or the car’s throwing EVAP codes after refuelling, a fresh cap is a cheap, quick win that can save diagnostic time and keep the Forester happy.

Popular questions about 1999 Subaru Forester fuel caps

What fuel cap part fits a 1999 Forester?
Most 1999 Forester (SF) models use a tethered, click-type EVAP cap commonly listed as Subaru 42031FC030, with some markets noting 42031AE020. A quality aftermarket equivalent is acceptable if it’s specified for the SF Forester and maintains EVAP sealing. Best practice is to confirm by VIN to account for market variations.

How often should the fuel cap be replaced?
There’s no fixed schedule. Inspect the seal at every service. Replace if the rubber is cracked, hard, or flattened, if the cap won’t click when tightened, or if there’s recurring EVAP leak faults after refuelling. On older vehicles, proactive replacement every decade or so is common sense given rubber ageing.

Why does the Check Engine Light come on after refuelling?
On these Foresters, a loose or worn fuel cap is a frequent cause of EVAP leak codes like P0440, P0442, or P0456. Ensure the cap is tightened until it clicks several times, then allow a few drive cycles for the monitor to re-check. If the light persists, inspect the cap seal and filler neck, and consider replacing the cap before chasing deeper EVAP leaks.