Key takeaways
P0455 means the engine computer sealed the evaporative emission (EVAP) system for a leak test and could not build or hold the vacuum or pressure it expected, so it found a large leak or a blocked purge path. With a steady light and no strong fuel smell you can usually keep driving, but check the gas cap first and fix the leak before your next emissions test.
- 01The usual suspects are a loose or worn gas cap, a disconnected EVAP hose, a stuck-open canister vent valve and, on Ford and GM vehicles, a purge valve stuck closed.
- 02The car runs its leak test only under set conditions, often with the tank between 15% and 85% full, so the light can take days to come back or go out.
- 03A strong smell of raw fuel changes the advice, because fuel vapor ignites easily: have the car checked right away.
- 04RepairPal's national estimates put a gas cap at $138 to $150 and a charcoal canister at $558 to $643, and Advance Auto Parts puts a shop smoke test at $60 to $150.
This guide belongs to our OBD2 guide: most common codes section, which covers the wider topic.
A P0455 code means your car's evaporative emission control (EVAP) system failed its own leak test by a wide margin. RepairPal's P0455 page says the code appears when the system cannot create enough vacuum during the test, usually because of an air leak, and that most drivers notice nothing beyond the light and, sometimes, a fuel odor.
The fix is often cheap, because a loose or worn gas cap tops most cause lists. Our table of the most common OBD2 codes and repair costs puts EVAP purge valve replacement at a $172 average, though that row lists purge-flow codes such as P0441 rather than P0455.
P0455 Quick Answer: What It Means and Can You Drive?
P0455 stands for "Evaporative Emission System Leak Detected (Large Leak)." With a steady light and no strong fuel smell, it is usually safe to drive while you track down the cause.
| Item | Detail |
|---|---|
| Code | P0455, Evaporative Emission System Leak Detected (Large Leak) |
| What it means | The EVAP system could not reach or hold its test vacuum or pressure |
| Most likely causes | Gas cap, EVAP hose, canister vent valve, purge valve stuck closed |
| Other causes to rule out | Filler neck, charcoal canister, fuel tank pressure sensor, fuel tank |
| Safe to drive? | Usually, with a steady light; get help fast if the fuel smell is strong |
| Typical repair cost | $138 to $150 for a gas cap, up to $1,686 to $1,892 for a fuel tank |
Code name from RepairPal and Ford. Causes from Ford, GM bulletin 21-NA-124, RepairPal and Advance Auto Parts. Costs are RepairPal national estimates updated September 3, 2026, before taxes and fees.
What the EVAP system does and why it's monitored
The EVAP system keeps fuel tank vapor out of the air. An EPA analysis of vehicle evaporative emissions explains that a canister stores the vapor in activated carbon until the car is driven, when the engine draws it in and burns it as fuel.
The parts run the length of the car. GM's leak checklist starts at the purge valve on the intake manifold and works back to the canister, vent valve and fuel tank, and Samarins says the vent valve usually sits at the back of the car, at or near the canister.
That 1993 analysis calls vehicle evaporative emissions a significant source of volatile organic compounds, which EPA's gasoline standards overview says contribute to ground-level ozone, or smog.
So OBD II checks the system for leaks. EPA's 30-vehicle study of OBD II evaporative monitors says 1996 to 1999 models must detect leaks the size of a 0.040-inch hole or larger, with 0.020-inch detection phased in over the 2000 to 2002 model years.
How Big Is a Large EVAP Leak?
"Large" means bigger than the leaks behind P0442 and P0456, but each carmaker writes its own test limits.
In Ford's OBD system operation summary for 2019 models, P0455 means the system could not even pull its initial test vacuum. P0442 is a 0.040-inch leak, and P0456 is a 0.020-inch leak found by a separate engine-off test.
Regulators set the minimums. CARB's 2002 OBD II rulemaking notes require separate monitoring for 0.020-inch and 0.040-inch leaks, with a provision to monitor for 0.090-inch leaks instead of 0.040-inch leaks if certain criteria are met.
Advance Auto Parts' P0455 guide puts the large-leak threshold at 0.040 inch or larger, but under Ford's definitions a 0.040-inch leak sets P0442. The cutoff depends on the carmaker, so treat any single number as a rough guide.
| Code | Name | What it usually points to | Leak size, where a source gives one |
|---|---|---|---|
| P0455 | EVAP leak detected (large leak) | Missing cap, disconnected hose, stuck-open vent valve | No test vacuum at all (Ford); 0.040 inch or larger (Advance) |
| P0442 | EVAP leak detected (small leak) | Stuck-open purge or vent valve, unsealed system | 0.040 inch (Ford) |
| P0456 | EVAP leak detected (very small leak) | Worn cap seal, cracked hose, leaking purge valve | 0.020 inch (Ford and Advance) |
| P0457 | EVAP leak detected (fuel cap loose/off) | Cap left loose after a fill-up | Set after a refueling event (Ford) |
From Ford's 2019 OBD System Operation Summary, GM bulletin 21-NA-124, Advance Auto Parts and OBDeleven. Not every vehicle uses P0457, and leak limits vary by carmaker.
How Your Car Tests for a Large Leak
The engine computer seals the EVAP system, applies vacuum or pressure to the fuel tank and watches whether it holds, as New York's NYVIP3 EVAP monitor page describes.
The engine-running vacuum test
Most large-leak checks run while you drive. Ford closes the canister vent solenoid, then opens the purge valve to pull 8 inches of water of vacuum from the engine. If that vacuum can't be reached, Ford logs a large leak, and 2009 and later models need two or three gross-leak failures in a row before setting P0455. NYVIP3 says the light generally comes on once a fault shows up on two drive cycles.
Mitsubishi's P0455 service page works the same way. The purge solenoid pulls the sealed system to 2 kPa (0.29 psi) of vacuum, then shuts, and the computer measures how the tank vacuum changes.
The engine-off natural vacuum test
Some cars also test after you park. Ford's engine off natural vacuum (EONV) test looks for 0.020-inch leaks with the ignition off, reading the pressure change as the warm tank cools. It can run until 45 minutes after key-off, up to two times a day.
Conditions that have to line up
The test runs only when conditions are right, so the light can take days to return or go out. Ford's highway test needs all of these:
- A fuel level between 15% and 85%
- An engine-off soak of 4 to 6 hours beforehand
- At least 330 seconds since the engine started
- Steady driving between 40 and 90 mph
- Outside air between 40°F and 100°F
- Altitude below about 8,000 feet
Entry conditions from Ford's 2019 OBD System Operation Summary. Other carmakers use different values.
NYVIP3's general guidance is similar: a tank 1/4 to 3/4 full, an outside temperature between 30°F and 95°F, and a car that has sat overnight or for at least 8 hours. It adds that any stored EVAP code keeps the monitor from running.
P0455 Symptoms
Usually the only sign is a steady check engine light. Samarins' P0455 page says a car with this code will not show any driveability issues in most cases.
When there is more, watch for these signs:
- A gas smell near the tank, cap or canister, which Advance Auto Parts says is stronger than with P0456
- A fuel smell inside the car, which OBDeleven lists as a common sign
- A hiss near the gas cap or under the car from a disconnected hose or stuck-open vent valve
- A loose fuel cap warning on cars that have one, such as 2012 and newer Nissans
- A fuel tank that is hard to fill, reported on some GM trucks
Symptoms from Samarins, Advance Auto Parts, OBDeleven and Nissan bulletin NTB13-097J.
What Causes P0455? Most Likely First
Start with the gas cap, which Advance Auto Parts ranks as the most common cause. The order below follows Advance's list, with the purge valve added from Ford and GM.
A loose, missing or worn gas cap
Nissan's EVAP leak bulletin NTB13-097J for 2012 and newer models says a cap left loose for multiple trips stores EVAP codes and turns on the light.
How tight is tight depends on the car. Kia's 2027 owner's manual says to tighten the cap until it clicks one time, otherwise the engine warning light will come on, while Mitsubishi's test procedure tightens it to three clicks.
A cap can look fine and still leak. RepairPal says a fuel cap pressure tester is the only accurate way to know whether a cap works, and that expecting more than 100,000 miles from one cap is not likely realistic. Samarins adds a faulty capless filler unit to the list for cars without a cap.
Disconnected or cracked EVAP hoses
Advance Auto Parts says a fully disconnected line is more likely to trigger P0455 than a cracked one. GM's bulletin 21-NA-124, which covers 2000 to 2021 GM gasoline cars and trucks, lists an unseated tube connection or a damaged tube among the P0455 causes. It names seven critical connections to check, from the purge tube at the intake manifold to the fuel tank load line jumper near the tank, with the gas cap as the seventh.
A canister vent valve stuck open
The vent valve is normally open and must close to seal the system for the test. If it sticks open, vacuum bleeds out, and Advance says this often shows up alongside P0446.
On the Silverado, Advance says it is the most frequent cause after the gas cap. It sits on the frame rail, where road debris, mud and water speed up solenoid failure. Samarins says a working vent valve clicks and closes when battery voltage is applied.
A purge valve stuck closed, or a blocked purge line
The purge valve has to open to pull the test vacuum, so if it can't, the computer sees no vacuum and reads a large leak. Ford's summary says a stuck-closed purge valve generates a P0455, and GM's bulletin lists purge blockage as a P0455 cause.
A purge valve stuck open is a split case. GM ties it to P0442, while RepairPal and Samarins say it can also set P0455. An open purge valve is also one of the unmetered air leaks behind a lean code, as our P0171 system too lean guide explains.
A cracked charcoal canister
Advance says canisters crack from road debris or fuel overfilling, and RepairPal says topping off the tank can fill the canister with fuel, degrading the charcoal and causing system failure.
The filler neck, fuel tank and their seals
Road-salt corrosion and debris can damage the filler neck or tank, which Advance says is more common in northern climates. An FCA technical case on EVAP leak codes has technicians check the cap's O-ring and look for gouges or paint chips in the filler tube's sealing area. O'Reilly Auto Parts also lists fuel tank sending unit gaskets or seals.
Sensors, pumps and less common parts
A failed fuel tank pressure sensor is on Advance's list too. OBDeleven's P0455 page adds that a malfunctioning leak detection pump can falsely indicate a leak. Mitsubishi also lists incorrect fuel cap relief pressure and a failed fuel overflow limiter valve.
How to Diagnose P0455 With a Scanner
Read the codes, check the cap and hoses, and only then pay for a smoke test. Freeze frame and readiness data help, as our roundup of the best OBD2 scanners for each budget explains.
- Read every code and save the freeze frame. Advance says P0441 alongside P0455 points to the purge valve and P0446 to the vent valve.
- Check the gas cap. Confirm it is there, seated and tightened until it clicks, then inspect the O-ring for cracks or debris.
- Clear the code and drive normally. Advance suggests two to three drive cycles. If the code returns, the leak is elsewhere.
- Inspect every EVAP hose you can see. Look for disconnected, cracked, melted or rodent-chewed lines from the tank to the engine.
- Command the valves if your scanner can. GM's bulletin says cycling the purge and vent solenoids with a scan tool while inspecting may reveal a sticking valve.
- Smoke test the system if you still haven't found the leak.
- Check for service bulletins before replacing a sensor, canister or tank.
- Fix, clear and confirm that the code stays away once the EVAP monitor completes.
Smoke testing the EVAP system
A smoke machine fills the system with visible vapor that escapes at the leak. Samarins notes that leak testing is difficult without proper equipment, so this is usually a shop job.
RepairPal tells technicians to close the vent valve during the test and watch the fuel tank pressure reading as smoke goes in. If the reading doesn't rise, the sensor may be failing the monitor rather than a leak. GM's bulletin adds that some leaks show up only under pressure and some only under vacuum, so test both ways when you can. FCA's case flags a trap: its smoke tool's cap adapter can mask a leak at the cap, so technicians leave the original gas cap in place during the test.
Why a dealer may not replace your gas cap
Nissan's bulletin has technicians pressurize the system with a special tool and watch it for 10 minutes. If it holds, they erase the codes, tell the owner to keep the cap secured and replace no EVAP parts.
Carmaker Bulletins That Mention P0455
Check for a bulletin before you buy parts.
| Vehicles | Bulletin | What it covers | Fix |
|---|---|---|---|
| 2000 to 2021 Buick, Cadillac, Chevrolet and GMC with gasoline engines | GM 21-NA-124 | P0442 or P0455 from leaks or purge blockage | Check seven EVAP connections, the lines, the vent valve, then the purge valve |
| 2021 and 2022 Chevrolet Express and GMC Savana with the 57-gallon tank | GM 21-NA-180 | P0455 or P0442, possible water in the fuel | Replace the fuel tank |
| 2015 Jeep Grand Cherokee and Dodge Durango built November 16, 2014 to January 17, 2015 | FCA 25-002-15 Rev. B | P0455 or P0456 from a split purge valve hose | Replace the purge valve vapor hose |
| 2012 and newer Nissan models, except LEAF and Titan XD diesel | Nissan NTB13-097J | P0442, P0455 or P0456, often from a loose cap | 10-minute pressure test; erase codes if no leak |
From the GM, FCA and Nissan bulletins filed with NHTSA. Each applies only to listed models or VINs, so confirm with a dealer.
GM's Express and Savana bulletin 21-NA-180 blames tank vents that may not be sealed to the tank. Because the vents are part of the tank assembly, technicians replace the tank rather than reseat them.
Is It Safe to Drive With P0455?
Usually, yes, if the light is steady and you can't smell much fuel. RepairPal rates P0455 "Moderate," a code that may not threaten safety right away but should be diagnosed within a reasonable time.
Two things change that. A strong fuel smell needs prompt attention, and OBDeleven warns that prolonged exposure to fuel vapor can cause headaches and breathing difficulties. Advance Auto Parts says P0455 alone will not cause a flashing light, so a flashing light means another fault. Don't wait months either, since Advance notes a lit light masks new codes.
| Situation | Severity | What to do |
|---|---|---|
| Steady light, no fuel smell, car runs normally | Moderate | Check the cap, then get it diagnosed soon |
| Strong smell of raw fuel in or around the car | High | Park outdoors away from sparks and have it checked right away |
| Flashing light or rough running | Severe, not from P0455 alone | Get immediate service and read every stored code |
| Emissions inspection due soon | Will likely fail | Fix it and let the monitors complete first |
From RepairPal, Advance Auto Parts, OBDeleven, the 2027 Kia owner's manual and the 2022 Ram 2500/3500 owner's manual.
Treat a strong gas smell as urgent
Fuel vapor ignites easily. Kia's manual warns that sparks from the engine's electrical parts can ignite fuel vapors and tells owners not to inhale them. If you smell raw gasoline, keep the car out of closed garages and have it inspected before driving far.
Free tool
Check Engine Light Checker. Say whether the light is steady, flashing or has gone off, and tick a recent fill-up or rough running, to get a Low risk, Act soon or Stop and check ruling.
The Check Engine Light Checker works from the light and your symptoms rather than the code, so use it alongside a scan.
If you haven't scanned the car yet, our guide on what to do when your check engine light comes on walks through scanning, looking up the code and deciding what to do next.
How to Fix P0455 and What It Costs
Fix what the tests point to, cheapest part first. RepairPal's emission system diagnosis estimate puts shop testing at $61 to $90.
| Repair | RepairPal estimate | Advance shop estimate | Advance DIY part |
|---|---|---|---|
| Gas cap replacement | $138 to $150 | $5 to $15 | $5 to $15 |
| Emission system diagnosis | $61 to $90 | Not listed | Not applicable |
| Smoke test | Not listed | $60 to $150 | $0 to borrow or rent |
| EVAP hose | Not listed | $75 to $200 | $5 to $20 |
| Vent valve | Not listed | $100 to $250 | $20 to $60 |
| Purge valve | $210 to $251 | Not listed | Not listed |
| Fuel tank pressure sensor | $356 to $457 | $150 to $350 | $30 to $80 |
| Charcoal canister | $558 to $643 | $200 to $400 | $50 to $150 |
| Fuel filler neck | Not listed | $200 to $500 | $50 to $150 |
| Fuel tank | $1,686 to $1,892 | Not listed | Not listed |
RepairPal national estimates for parts and labor, updated September 3, 2026, before taxes and fees. Advance Auto Parts figures from its P0455 guide, last updated September 11, 2026. The sources use different methods, so their figures differ.
The gas cap gap is large. RepairPal's gas cap estimate assumes parts around $114 plus $24 to $36 in labor, while Advance lists $5 to $15 for the part. RepairPal adds that some vehicles need a dealer cap, because a poorly matched cap cannot seal the system.
The 2026 CarMD Vehicle Health Index ranks EVAP purge valve replacement sixth among 2025 check engine repairs, averaging $172.12, and says gas cap repairs dropped off its list largely because of capless designs, driver education and courtesy diagnostics.
Free tool
Repair Cost Estimator. Enter a shop's parts price, labor hours, labor rate and fees to see the total and the parts-only DIY cost, then pick "EVAP purge control valve" to compare a purge valve quote with its $172 national average.
The Repair Cost Estimator splits a canister or purge valve quote into parts, labor and fees, so you can see how much of the bill is shop time.
After the Repair: Readiness Monitors and Emissions Inspections
Clear the code only after the repair, then let the car rerun its EVAP test. EPA's 1995 OBD rule lets the light go out on its own if the malfunction doesn't recur during three subsequent sequential trips in which the monitor runs. Once the cap is secured, Ford clears its cap-off code and lights when normal purge vacuum exceeds the level stored at the cap-off event.
Clearing codes also resets the readiness monitors. The New York DMV's readiness guide says that usually takes two drive cycles separated by a cool-down period, driven in a mix of highway and city traffic with the tank half to three-quarters full. Under EPA guidelines, a 2001 or newer vehicle may have one monitor not ready and still pass.
California is stricter. The Bureau of Automotive Repair's permanent code article says permanent codes have failed Smog Check on 2010 and newer vehicles since July 1, 2019. They can't be cleared with a scan tool or by disconnecting the battery, and the article singles out the EVAP leak codes P0442 and P0456 for gasoline and flex-fuel cars. BAR ignores a permanent code only after 15 warm-up cycles and 200 miles since the codes were last cleared, a limit meant for slow monitors.
EPA has backed separate cap checks. Its 30-vehicle study found that, in Wisconsin's inspection data, gas cap failures on 1998 OBD vehicles were over 30 times as common as evaporative failures the OBD monitor caught, and EPA recommended a standard gas cap check alongside the OBD scan.
Codes Related to P0455
P0455 often arrives with other EVAP codes, and OBDeleven names P0440, P0441, P0442 and P0457 as common companions.
| Code | Meaning | What it tells you |
|---|---|---|
| P0440 | EVAP system malfunction | A general EVAP fault |
| P0441 | EVAP improper purge flow | Points to the purge valve |
| P0442 | EVAP small leak detected | A smaller leak; a stuck-open purge or vent valve on GM |
| P0446 | EVAP vent control circuit | Points to the vent valve |
| P0456 | EVAP very small leak detected | A 0.020-inch leak with similar causes |
| P0457 | EVAP leak detected (fuel cap loose/off) | The cap was left loose after a fill-up |
| P0496 | EVAP high purge flow | Excessive vacuum; replaces Ford's P1450 |
Code names from OBDeleven, Advance Auto Parts and Ford's 2019 OBD System Operation Summary. Notes from Advance Auto Parts, GM bulletin 21-NA-124, Ford and Samarins.
O'Reilly Auto Parts lists P0455 among the most common check engine codes alongside the catalyst codes P0420 and P0430, and our guide to the P0420 catalyst system efficiency code covers the first of them.
Frequently Asked Questions
Will P0455 clear itself?
It can, once the leak is gone. EPA's OBD rules let the light go out after three trips in a row in which the EVAP monitor runs without finding the fault, and Ford clears its cap-off code once normal purge vacuum exceeds the level it stored. If the leak is still there, the test fails again and the light stays on or comes back.
Can overfilling the gas tank cause P0455?
It can contribute. RepairPal says overfilling can let fuel reach the charcoal canister, which may cause system failure and damage the canister, and Advance Auto Parts lists overfilling as one way canisters crack. Kia's owner's manual tells drivers not to overfill the tank. If the code appeared right after a fill-up, check the cap first, since it is the more common cause.
Can a new gas cap cause P0455?
Yes, if it does not seal. Kia's owner's manual says an incorrect fuel filler cap can cause a serious malfunction of the fuel system or emission control system, and it recommends a genuine cap or the specified equivalent. Advance Auto Parts says to choose a cap that matches your year, make and model and to tighten it until it clicks.
Is P0455 a permanent code?
EVAP leak codes can be stored as permanent codes. California's Bureau of Automotive Repair says permanent codes on 2010 and newer vehicles cannot be cleared with a scan tool or by disconnecting the battery and only clear when the monitor runs again without finding the problem. BAR's newsletter singles out the EVAP leak codes P0442 and P0456 for gasoline and flex-fuel cars.
Can cold weather cause P0455?
Cold mainly decides whether the test runs at all. NYVIP3 says the EVAP monitor generally needs an outside temperature between 30 and 95 degrees, Ford's engine-off test needs 40 to 95 degrees at start-up, and its highway test needs 40 to 100 degrees. In a long cold spell, the monitor may not get a chance to run, so the light can take longer to go out after a repair.
What does P0455 mean on a Nissan?
It means the same large EVAP leak, and Nissan says a loose fuel cap may be the cause on 2012 and newer models. Its bulletin NTB13-097J notes these cars have a loose cap warning, says a test drive is not part of confirming the code, and has dealers run a 10-minute pressure test. If no leak shows, they erase the codes without replacing parts.
Sources and References
- Advance Auto Parts. P0455: EVAP System Large Leak Detected
- O'Reilly Auto Parts. Check Engine Light DTC Code P0455: Evaporative Emission System Leak (Large Leak)
- OBDeleven. P0455: Evaporative Emission Control System Gross Leak Detected
- Samarins. P0455 Evaporative Emission Control System Leak Detected (Large Leak)
- RepairPal. P0455 OBD-II: Evaporative Emission System Leak Detected (Large Leak)
- RepairPal. Emission System Diagnosis & Testing Cost Estimate
- RepairPal. Gas Cap Replacement Cost Estimate
- RepairPal. Purge Valve Replacement Cost Estimate
- RepairPal. Fuel Tank Pressure Sensor Replacement Cost Estimate
- RepairPal. Fuel Evaporative Canister Replacement Cost Estimate
- RepairPal. Fuel Tank Replacement Cost Estimate
- CarMD. 2026 CarMD Vehicle Health Index
- Ford Motor Company. 2019 MY OBD System Operation Summary for Gasoline Engines
- Mitsubishi Motors. DTC P0455: Evaporative Emission System Leak Detected (Gross Leak)
- General Motors (via NHTSA). Bulletin 21-NA-124: Diagnostic Tip for Malfunction Indicator Lamp (MIL) Illuminated, DTC P0442 and/or P0455 Set
- General Motors (via NHTSA). Bulletin 21-NA-180: Information on Illuminated Check Engine Light, Possible Water in the Fuel, Evaporative Codes Set, Fuel Tank Evaporative Vent Valve Leak
- FCA US (via NHTSA). Service Bulletin 25-002-15 Rev. B: P0455/P0456 Set in the Powertrain Control Module (PCM)
- FCA US (via NHTSA). STAR Online Publication S2025000004: Customer Complains of the MIL Lamp On (P0456/P0455)
- Nissan (via NHTSA). NTB13-097J: EVAP Leak DTC P0442, P0455, P0456 Information
- Kia. 2027 Kia Owner's Manual: Closing the Fuel Filler Door
- Mopar (Ram). 2022 Ram 2500/3500 Owner's Manual: Engine Check/Malfunction Indicator Warning Light
- U.S. EPA. Final Regulatory Impact Analysis and Summary and Analysis of Comments: Control of Vehicular Evaporative Emissions (February 1993)
- U.S. EPA. Learn About Gasoline
- U.S. EPA. Effectiveness of OBD II Evaporative Emission Monitors: 30 Vehicle Study (EPA420-R-00-012)
- U.S. EPA (Federal Register). Regulations Requiring On-Board Diagnostic Systems: Revision to Requirements for Storage of Engine Conditions Associated With Extinguishing a Malfunction Indicator Light (August 2, 1995)
- California Air Resources Board. Attachment IV: Proposed Modifications to Malfunction and Diagnostic System Requirements (OBD II), Section 1968.2
- New York Vehicle Inspection Program (NYVIP3). EVAP System Monitor
- New York State DMV. What Do You Mean My Car's Not Ready?
- California Bureau of Automotive Repair. Permanent Diagnostic Trouble Codes (Automotive Repair and Smog Check News, Fall 2019)
Written by
CarTipsMentor Team
Researched from the sources listed above and checked against them before publishing. Nobody paid to be mentioned on this page. It is general information, not advice about your own vehicle.
Published . Last updated .
