GMC Sierra 1500 P0455 — EVAP Large Leak

GMC-specific code — factory diagnostic data

Last updated: May 14, 2026

Definition source: GMC factory description. Diagnostic guidance is based on factory-defined fault logic for this code.

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P0455 Quick Answer

P0455 on a Sierra means the EVAP system can’t hold any vacuum during the self-test. The #1 cause is the gas cap — a loose or worn-gasket cap that doesn’t seat properly. #2 is a cracked EVAP hose at the canister or purge valve. #3 is the canister vent solenoid stuck open. Most P0455s on Sierras are a $0-$30 fix.

What Does P0455 Mean on a GMC Sierra 1500?

The GMC Sierra 1500 (2007-2019) shares the GMT900 / K2XX chassis and Gen-IV LS engine families with the Chevy Silverado 1500. P0455 root causes match the Silverado pattern exactly. The model-specific failure modes documented below apply to all Sierra trim levels using the same engine.

Symptoms

• Check Engine Light (P0455)
• No driveability symptoms
• Possible faint fuel smell near rear of truck after refueling
• OBD-II inspection failure
• No effect on fuel economy or performance

Common Causes (Most Likely on This Model First)

1. Loose or worn fuel cap. A cap that doesn’t seat (under-tightened or hardened gasket) fails the EVAP test. Tighten to 3 clicks; replace if the gasket is cracked.
2. Cracked EVAP hose. Plastic quick-connect hoses near the canister (frame-mounted, under the bed) crack at fittings in cold climates. Inspect by hand — every connect should feel firmly seated.
3. Canister vent solenoid stuck open. Located on the EVAP canister. Spider webs and road debris contaminate the vent on trucks driven on dirt roads.
4. Cracked EVAP canister. Impact damage from rocks under the bed.
5. Failing fuel tank pressure sensor. Reports incorrect tank pressure — falsely triggers a leak code. Rare.

Diagnostic Approach

1. Tighten the fuel cap fully (3 clicks). Clear the code. Drive 50+ miles. If P0455 doesn’t return, you’re done.
2. If P0455 returns, inspect cap gasket. Worn = replace ($15-$25).
3. Smoke-test the EVAP system from the service port. Look for smoke at hose joints, canister vent, or canister body.
4. Bidirectional command the canister vent solenoid and watch tank pressure.
5. If smoke and vent both check good, suspect the fuel tank pressure sensor.

Possible Fixes

Can I Still Drive With P0455?

Yes — no effect on engine operation or safety. The only real-world impact is failing OBD-II inspection. Defer indefinitely if inspection isn’t required.

How Serious Is This Code?

Low. Cosmetic / regulatory only. Usually a trivial cheap fix.

Repair Costs