P0455
Evaporative Emission Control System Leak Detected (gross leak)P0455 is a generic OBD-II powertrain diagnostic trouble code: Evaporative Emission Control System Leak Detected (gross leak). It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0455 means
Code P0455 is set when the Engine Control Module (ECM) detects a large or gross leak in the Evaporative Emission Control (EVAP) system. The EVAP system is designed to capture fuel vapors from the fuel tank and route them through a charcoal canister into the intake manifold for combustion, preventing raw hydrocarbons from venting into the atmosphere. A leak of this magnitude means the system cannot hold the vacuum or pressure required during the ECM's periodic self-test (typically a closed-loop smoke/vacuum decay test run under specific driving conditions).
The most common cause by far is a loose, missing, or faulty fuel filler cap — the cap either was not tightened fully after refuelling or its rubber sealing ring has deteriorated. Beyond the cap, cracked or disconnected EVAP hoses, a stuck-open purge solenoid valve, a stuck-open vent control valve, or a damaged charcoal canister can all allow vapour to escape at a rate the ECM classifies as gross. The MIL (Check Engine light) illuminates and a DTC is stored after the monitor detects the failure on one or two consecutive drive cycles, depending on the manufacturer.
P0455 is an SAE generic powertrain code present across all OBDII-compliant vehicles (1996 onward). It does not typically cause drivability problems or trigger limp mode, but it represents a confirmed emissions compliance failure and may cause a noticeable fuel-vapour odour inside or around the vehicle. Related codes P0442 (small leak) and P0456 (very small leak) indicate progressively smaller leak thresholds on the same monitor.
Common causes
Most-frequently reported root causes when P0455 is logged.
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1
Loose, missing, or improperly seated fuel filler cap
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2
Damaged or deteriorated gas cap sealing ring
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3
Stuck-open EVAP purge solenoid valve
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4
Stuck-open EVAP vent control valve
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5
Cracked or disconnected EVAP hoses or tubing
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6
Damaged or saturated charcoal (vapour) canister
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7
Cracked or leaking fuel tank
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8
Refuelling with the engine running (can overwhelm canister and trigger monitor)
Symptoms drivers notice
How to diagnose P0455
A typical diagnostic flow when this code is present.
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1
Inspect the fuel filler cap first: remove, examine the sealing ring for cracks or dry rot, reinstall firmly until the torque-limiter clicks, clear the code, and complete a full drive cycle to see if it resets
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2
Perform a visual inspection of all accessible EVAP hoses, lines, and connections from the fuel tank to the charcoal canister and intake manifold for cracks, kinks, or disconnections
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3
Test the EVAP purge solenoid valve: apply 12 V directly and listen for an audible click; apply vacuum to confirm it holds closed when de-energised
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4
Test the EVAP vent control valve: apply vacuum to confirm it holds when commanded closed; inspect for debris blocking the seat
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5
Perform a professional smoke test on the sealed EVAP system with a UV-dye smoke machine to locate any gross leak point that is not visually obvious
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6
Inspect the charcoal canister for physical damage, saturation (liquid fuel present), or broken ports
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7
Check fuel tank integrity and filler neck for corrosion, cracks, or damage if all upstream components test good
Related powertrain codes
- P0400 — Exhaust Gas Recirculation Flow Malfunction
- P0401 — Exhaust Gas Recirculation Flow Insufficient Detected
- P0402 — Exhaust Gas Recirculation Flow Excessive Detected
- P0403 — Exhaust Gas Recirculation Circuit Malfunction
- P0404 — Exhaust Gas Recirculation Circuit Range/Performance
- P0405 — Exhaust Gas Recirculation Sensor A Circuit Low
Frequently asked questions
Can I drive safely with a P0455 code?
Yes, in most cases P0455 does not affect engine performance or safety. However, you should address it promptly because the vehicle will likely fail an emissions inspection, fuel vapours represent a minor fire hazard, and on some vehicles an open purge valve can eventually cause rough running or poor fuel economy.
Will tightening the gas cap fix P0455?
It will fix the code if a loose or unseated cap is the root cause, which accounts for the majority of P0455 cases. After tightening (or replacing) the cap, clear the DTC and complete at least one full drive cycle. If the code does not return, the cap was the culprit. If it returns, further diagnosis of the EVAP system is needed.
What is the difference between P0455, P0442, and P0456?
All three codes indicate an EVAP system leak detected during the ECM's vapour-pressure decay self-test, but at different thresholds. P0456 is a very small leak (typically less than 0.020 inch orifice equivalent), P0442 is a small leak (around 0.020–0.040 inch), and P0455 is a gross or large leak (greater than 0.040 inch equivalent) — meaning P0455 represents the most severe leak the monitor can detect.
How much does it cost to repair a P0455?
Repair cost depends entirely on the root cause. A replacement fuel filler cap costs roughly $10–$30 and is a DIY repair. An EVAP purge or vent solenoid valve typically costs $20–$80 in parts plus one hour of labour. A charcoal canister replacement can range from $150–$600 depending on vehicle. A smoke test at a workshop to locate a non-obvious leak usually costs $75–$150 as a diagnostic fee.
Disabling P0455 in software
RaceTune can permanently disable P0455 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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