OBD-II Diagnostic Trouble Code
P0455 — Evaporative Emission System Leak Detected (large leak)
P0455 indicates the EVAP leak test found a large leak, or the system could not develop vacuum at all. The ECM closed the vent valve and opened purge but saw little or no change in tank pressure. Applies to gasoline-fueled trucks.
Severity 2/5
Less common on commercial trucks
Service soon
Severity
Service soon
Evaporative Emission System Leak Detected (large leak)
Code
P0455
Category
Powertrain
Subsystem
Emissions
Truck-relevant
Less common
What this means for truckers
P0455 (EVAP Large Leak) — gas engine. Bigger leak than P0442 — usually disconnected hose or missing gas cap. Visual inspection should find it quickly.
Before you replace parts — try this first
P0455 on the Emissions system is most often fuel cap missing, loose or not sealing — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Check-engine light and often a noticeable fuel smell around the truck. Some trucks show a 'check fuel cap' message. Driveability is usually normal.
Common causes
- CommonFuel cap missing, loose or not sealing ($20–$60)
- CommonDisconnected or split EVAP hose ($100–$300)
- OccasionalPurge valve stuck closed so no vacuum is drawn ($150–$400)
- OccasionalCracked canister or leaking filler neck ($250–$900)
How to fix
Check that the fuel cap is present, correct and tightened; replace if the seal is damaged
When to use: First step
Visually inspect EVAP lines from tank to canister to engine for disconnections
When to use: When the cap is good
Smoke test the system to find the leak
When to use: When no obvious damage is visible
Test purge valve operation
When to use: When no leak is found by smoke testing
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0400 — Exhaust Gas Recirculation Flow Malfunction
- → P0401 — Exhaust Gas Recirculation Flow Insufficient Detected
- → P0402 — Exhaust Gas Recirculation Flow Excessive Detected
- → P0420 — Catalyst System Efficiency Below Threshold (Bank 1)
- → P0421 — Warm Up Catalyst Efficiency Below Threshold (Bank 1)
Frequently Asked Questions
Can I drive with code P0455?
P0455 is severity 2 — service this week. Not an immediate stop, but ignoring it usually compounds the problem. Most common cause for this code is a worn sensor or minor performance fault that won't strand you today but will get more expensive the longer you wait.
How much does it cost to fix P0455 on a commercial truck?
Total repair cost ranges $20–$900 depending on the root cause. The cheapest fix is usually the first one listed below — Fuel cap missing, loose or not sealing — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0455 fail a DOT inspection?
Yes — P0455 is an emissions-related code, and DOT inspectors check emissions compliance. An active emissions code with a check engine light can result in an out-of-service violation under FMCSA Part 393. The truck typically can't be moved until the code is cleared. Repeated emissions violations escalate to CSA scores.
What's the difference between P0455 and related codes?
P0455 is closely related to: P0400 (Exhaust Gas Recirculation Flow Malfunction), P0401 (Exhaust Gas Recirculation Flow Insufficient Detected), P0402 (Exhaust Gas Recirculation Flow Excessive Detected), P0420 (Catalyst System Efficiency Below Threshold (Bank 1)). These codes share the same subsystem (emissions) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0455 is set without the companions, the issue is more isolated.
How do I prevent P0455 from coming back after a repair?
For P0455 (Evaporative Emission System Leak Detected (large leak)), prevention centers on the emissions system. Keep up with PM on the EGR system — clean the valve at 200K miles. Use OEM-spec air filters. Don't ignore minor codes; they often escalate into bigger emissions failures.