Rick's Free Auto Repair Advice

P0455 code: What it means and how to fix it

Learn how to diagnose and fix a P0455 code — Evaporative Emission Control System Leak Detected (Gross Leak)

If your vehicle’s check engine light is illuminated and you retrieve a P0455 code, that means you have an issue with the Evaporative Emission (EVAP) Control System. This system is designed to prevent gasoline vapors from escaping into the atmosphere. A P0455 code specifically points to a leak detected in the EVAP system.

The Evaporative Emissions system applies a vacuum to the fuel system after you fill with gas. If the system can’t hold the vacuum, it knows there’s a major leak. This is usually a sign that you’ve left the gas cap off or that the gas cap is not sealing properly against the neck of the filler tube.

First, check the gas cap to make sure it’s tight. If it is, remove the cap and check the condition of the “O” ring seal and the neck of the filler tube. If the gas cap “O” ring is worn or damaged, replace it. Some car makers sell the “O” ring, but most make you buy a new gas cap. If you’re close to a dealer, buy it from them rather than a generic one from the parts store. You’ll have better luck over the long haul with an OEM part.

Understanding the EVAP System

The EVAP system captures fuel vapors from the gas tank, using a canister filled with activated charcoal. Once you start the engine, it sucks the vapors out of the canister and burns them in the engine. The Evaporative Emissions System consists of several components, including the gas tank, vapor lines, purge valve, vent control valve, and a charcoal canister. If any part of this system develops a leak, the engine computer will set the P0455 code.

Check these items first

• Check for Loose Gas Cap: One of the most common causes of a P0455 code is a loose or faulty gas cap. Tighten the gas cap and see if the code clears after a few drive cycles.
• Perform a visual inspection of the EVAP system components, including the vapor lines, purge valve, vent control valve, and charcoal canister. Look for any signs of damage, cracks, or loose connections that could indicate a leak.

Image of evaporative emissions components. Purge valve, vent valve, fuel tank pressure sensor, and charcoal canister

If the leak still exists, test the purge and vent valves

Using a handheld vacuum pump, apply a vacuum to the purge valve and the vent valve to see if they hold vacuum. You may have to use jumper wires to provide power and ground to operate the solenoid valves. Replace either valve if it fails to hold vacuum.

If you notice any charcoal particles in the purge valve, that’s an indication that the canister has failed and is spewing charcoal into the purge line. Replace the canister, flush the lines and replace the purge valve to restore the system to operating condition.

Next, apply vacuum to the Charcoal Canister. If it won’t hold vacuum, it’s leaking and must be replaced.

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat

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