P0455
EVAP system large leak detected
Severity: MonitorEVAP (evaporative emissions) codes
The EVAP system traps gasoline vapor from the fuel tank in a charcoal canister and later lets the engine draw that vapor in and burn it, a process called purging. The engine computer seals the system and checks it for leaks, and it also checks that purge flow actually reaches the engine. Most EVAP faults raise emissions rather than affect how the car drives.
How these codes differ
- P0455, P0442 and P0456 come from the same leak test and differ only in the size of leak it found. Regulations require the computer to catch a leak as small as a 0.040-inch hole (P0442 is the usual small-leak code) and, on newer cars, as small as a 0.020-inch hole (P0456, very small leak). P0455 means the system could not hold vacuum or pressure at all, which points first to an open or missing gas cap, a disconnected hose or a valve stuck open rather than a pinhole.
- Because the leak size narrows the search, the test order changes: for P0455 check the gas cap and obvious disconnected hoses before anything else; for P0456 a smoke test is usually needed because the leak is too small to find by eye or by listening.
- P0441 and P0497 are about purge flow, not leaks: the computer commanded the purge valve open and did not see the expected change (for example in fuel trim or manifold pressure). P0496 is the opposite case: vapor is flowing into the engine when the purge valve should be closed, which points to a purge valve stuck open.
- P0443 is an electrical fault in the purge valve circuit (open, short or wrong resistance), while P0441/P0496 mean the valve's circuit looks fine but the flow is wrong. Test wiring for P0443; test the valve's mechanical sealing for P0496.
- P0446 and P0449 concern the vent side of the canister. The vent valve must close to seal the system for the leak test, so a vent fault can also stop the leak test from running or make it fail. P0449 is the vent valve's electrical circuit; P0446 is the vent control's performance (for example a valve that does not seal or a blocked vent path).
- P0451 is a range or performance fault in the fuel tank pressure sensor, the sensor the leak test relies on, so a bad reading there can make leak results untrustworthy. P0457 means the computer concluded the leak is at the fuel cap itself (loose or missing), which is the one EVAP case the regulation allows the computer to clear once the cap is secured.
- P0440 is a general EVAP malfunction code; on many vehicles a more specific code (leak size, purge or vent) is stored with it and should be followed first.
Codes that show up together
- A leak code (P0455, P0442 or P0456) together with P0496 points toward a purge valve that is stuck open, because an open purge valve both lets vapor in when it should not and keeps the system from sealing for the leak test.
- P0446 or P0449 with a leak code: fix the vent valve first, because the leak test cannot seal the system until the vent closes properly.
- P0457 or P0455 that appears right after refuelling usually leads back to the gas cap; tighten or replace it and let the computer re-run its test before chasing other parts.
EVAP (evaporative emissions) codes
P0442
EVAP system small leak detected
Severity: MonitorP0456
EVAP system very small leak detected
Severity: MonitorP0441
EVAP purge flow incorrect
Severity: MonitorP0446
EVAP vent control performance problem
Severity: MonitorP0449
EVAP vent valve circuit fault
Severity: MonitorP0496
EVAP purge flow when purge should be off
Severity: MonitorP0440
EVAP system fault (general)
Severity: MonitorP0443
EVAP purge valve circuit fault
Severity: MonitorP0451
Fuel tank pressure sensor reading out of its expected range
Severity: MonitorP0457
EVAP leak detected from the fuel cap being loose or off
Severity: MonitorP0497
EVAP system low purge flow
Severity: MonitorP1450
Fuel tank vacuum not bleeding off (Ford, Lincoln, Mazda)
Severity: MonitorP144A
On Ford vehicles, the EVAP system's purge vapor line is restricted or blocked
Severity: MonitorP2402
EVAP leak detection pump control circuit high
Severity: MonitorP043E
EVAP reference orifice flow too low
Severity: MonitorP0452
EVAP pressure sensor reading too low
Severity: MonitorP2401
Leak detection pump circuit reading low
Severity: MonitorP2419
EVAP switching valve circuit reading low
Severity: MonitorP043F
EVAP leak-test reference check reads too much flow
Severity: MonitorP0445
EVAP purge valve circuit shorted
Severity: MonitorP0448
EVAP vent valve circuit shorted
Severity: MonitorP144C
On Ford vehicles, the EVAP purge check valve or vapor ejector path is not performing
Severity: MonitorP2422
EVAP vent valve will not open, so fresh air cannot get into the fuel vapour system
Severity: MonitorP04F0
EVAP purge flow is not as expected when the engine is under high load (purge line A)
Severity: MonitorP1456
Honda: leak found in the EVAP control system on the fuel tank side
Severity: MonitorP2450
EVAP switching valve (fuel tank isolation valve) not working as commanded
Severity: MonitorP1446
Nissan EVAP canister vent control valve fault (valve closed)
Severity: Severity not verifiedP0444
The computer sees an open circuit on the EVAP purge control valve
Severity: Severity not verifiedP0447
EVAP vent control circuit is open (no proper signal from the vent valve circuit)
Severity: MonitorP0450
EVAP pressure sensor malfunction
Severity: MonitorP0453
The evaporative system pressure sensor is sending a voltage that is too high
Severity: MonitorP0458
The computer sees a low voltage on the EVAP purge control valve circuit
Severity: Severity not verifiedP0468
EVAP purge flow sensor signal reading too high
Severity: Severity not verifiedP0469
EVAP purge flow sensor signal dropping in and out
Severity: Severity not verifiedP0498
EVAP vent valve control circuit low: the wire to the valve that seals the fuel vapour system is reading too low
Severity: MonitorP0499
EVAP vent valve control circuit high: the wire to the valve that seals the fuel vapour system is reading too high
Severity: MonitorP04F1
EVAP system low purge flow: the computer sees less fuel vapour moving from the charcoal canister to the engine than expected
Severity: Severity not verifiedP1457
On Honda and Acura, the engine computer found a leak or fault in the EVAP canister side of the fuel vapor system
Severity: MonitorP2421
The EVAP vent valve is reported stuck open
Severity: MonitorP0454
Evaporative emission control system pressure sensor signal is intermittent
Severity: Severity not verified
Sources and review
- Final Regulation Order: 13 CCR §1968.2, Malfunction and Diagnostic System Requirements (OBD II), 2004 and subsequent model-year passenger cars, light-duty trucks and medium-duty vehicles (2015 amendments)
- 40 CFR §86.1806-04 On-board diagnostics (2011 edition page, includes the end of §86.1806-01(k) malfunction criteria)
- OBD: Frequently Asked Questions (EPA420-F-02-014, rev. September 2012)
- OBD consumer brochure: Do you drive a 1996 or newer car or light truck? (EPA420-F-02-016)
- Vapor Trails: Finding & Fixing Evaporative System Faults (Bob Pattengale)
- Frequently Asked Questions About On-Board Diagnostics (EPA 420-F-97-003)
- What To Do With the Check Engine Light (EPA420-F-00-041)
- Vapor Canister Purge Valve
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error