Powertrain, generic · Auxiliary emission controls

P0457 EVAP System Leak Detected (fuel cap loose/off)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. P0457 is a large leak attributed to the fuel cap: Ford detects refuelling and treats a vacuum that is not reached afterwards (about −2 kPa in 30 s) as an open cap. CARB allows a separate check fuel cap lamp instead of the warning lamp, and the code is cleared once the cap is found tight again. Ford sets the lamp after two to three trips depending on calibration, Subaru after two. GM and Saab's ME9 do not use the code.

Likely causes

Fuel cap not closed, not clicked in or forgotten
Fuel cap seal faulty or non-original cap
Filler neck sealing surface damaged or capless flap sticking
Vent valve stuck open

Symptoms

  • Check fuel cap lamp or check engine light on
  • Fuel smell
  • EVAP readiness not set

Repair estimate

DifficultyEasyDIY possible
Parts and labour€0–60
Time0–0.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Tighten or replace the fuel cap
  2. Inspect the filler neck

Parts involved

fuel capfuel filler neckevap system

Related codes

P0455P0442P0456P0446P0464

References: newtonnet.co.uk, fordservicecontent.com, saabwisonline.com, law.cornell.edu.