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The Gas Cap In Your EVAP System

If the OBD II system can tell a leak is from a missing or loose cap, the maker does not have to turn on the MIL if the car has a separate warning light. Without one, the MIL may go off once the system verifies the cap is tight and no other fault is present.

What The Sources Say About It

  • If the OBD II system can tell a leak is from a missing or loose cap, the maker does not have to turn on the MIL if the car has a separate warning light. Without one, the MIL may go off once the system verifies the cap is tight and no other fault is present. (source)
  • Ford may show a Check Fuel Cap light with P0457. Once the cap is secured, the code, light and MIL clear as soon as normal purge vacuum passes the stored level. (source)
  • Honda's P1456 steps say to tighten the cap at least three clicks, and that damage to the fill neck, sealing surface or threads can cause a leak. (source)
  • Acura found some caps had a gasket with too much friction, so the cap felt loose or sticky and did not seal (P0455 or P0456). (source)
  • FCA says do not remove the original gas cap during a smoke or leak test. A test adapter in its place can hide the leak. (source)

Codes That Point Here

P0455Evap Emission Control System Gross Leak DetectedP0456Evap System Very Small LeakP0457Evap Emission System Leak Detected (fuel Cap Loose/off)

What It Costs

Published estimates put a gas cap at $138 to $150 at RepairPal. See every price row. For a real example of pricing the test before the part, see how we priced a fuel leak diagnosis.

Anthony Limpert in a Supercanic shirt
By , co-founder of Supercanic in San Jacinto, California, a shop with ASE certified mechanics. Updated November 12, 2026.

Author Source EEAT Authors · Anthony's Author Page

Sources For This Page

  1. 13 CCR 1968.2, Malfunction and Diagnostic System Requirements, OBD II, California Air Resources Board (via Cornell LII), read 2026-11-12
  2. 2009 MY OBD System Operation Summary for Hybrid Electric Vehicles (revised May 22, 2008), Ford Motor Company, read 2026-11-12
  3. Service Bulletin 99-075, Troubleshooting DTC P1456 and P1457 (August 9, 2013), American Honda Motor Co., read 2026-11-12
  4. Service Bulletin 14-006, MIL Comes On With DTC P0455 and/or P0456 (February 18, 2014), American Honda Motor Co. (Acura), read 2026-11-12
  5. STAR Online case S2025000004, P0456 or P0455 (April 28, 2020), FCA US LLC, read 2026-11-12
  6. Gas Cap Replacement Cost Estimate, RepairPal, read 2026-11-12
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