Fix P0455: Mechanic’s solutions that WORKED

P0455 Evaporative Emission Control System Leak Detected (Gross Leak) points to a large leak in your EVAP system and is caused by a stuck purge control valve or a loose or aftermarket gas cap that doesn’t fully seal the gasoline system.

The code is similar to P0442 (EVAP small leak detected).

P0455 quick overview

Meaning	“Evaporative Emission Control System Leak Detected (Gross Leak)”
Is it serious?	It’s not an emergency, but it needs attention. It affects emissions.
Possible causes	– Loose gas cap – Leaky hoses or valves – Stuck purge control valve – Other issues (MAF sensor in example below)
How to fix	– Check the gas cap – Look for leaks in hoses or valves – If you smell gasoline, get a smoke test to find leak – Is it running lean/rich? Solve other issue first, it might fix EVAP as well
What is EVAP?	The Evaporative Emission Control System (EVAP) is a crucial part of your car’s emission control, preventing fuel vapors from escaping into the air and contributing to pollution. This system includes key components like: Gas Tank: Stores fuel. Charcoal Canister: Acts as a vapor trap. Valves: Open and close to control vapor flow. Hoses: Connect components for vapor movement. Sensors: Keep track of the system’s status. During operation, stored vapors are sent back to the engine to burn, reducing emissions. If there’s a leak or malfunction, it triggers warning codes like P0455, indicating potential issues with this emission-control setup.

How to fix P0455 – learn from mechanics

I looked into P0455 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics.I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Ford

Vehicle Information:
1998 Ford Expedition Eddie Bauer
Engine: 4.6L

Issue + Repair History:

• The customer reported spark knocks under light acceleration with no misfire or flutter.
• The issue occurred regardless of engine temperature.
• The only trouble code found was P0455 (Evaporative Emission System Leak Detected).
• The engine had been replaced with a used motor at another shop, and the spark knock issues started afterward.
• The P0455 code indicated a sensor shorted.

Suggestions from the Community:

• Some mechanics suggested that a dirty MAF sensor could cause spark knock; cleaning and relearning the MAF might resolve the issue.
• Others recommended checking for carbon buildup in EGR ports and considering a PCM reflash update.
• Emphasized the importance of checking for a vacuum leak causing a lean condition, with a focus on the MAF sensor.
• Suggested inspecting the EGR system for clogging or restriction.
• A few mentioned the possibility of a vacuum leak in the PCV harness and clogged EGR passages under the lower throttle body.

Final Fix:
The suggestion to check the MAF sensor was accurate. The MAF sensor was found to be shorted, causing a lean condition. Replacing the MAF sensor fixed both the spark knock issue and the P0455 code.

Case #2: Mazda

Vehicle Information:
2006 Mazda 5 Sport
Engine: 2.3L

Issue + Repair History:

• The vehicle would cut out and stall, especially after filling up with gas.
• The engine would act up initially, then run fine until the next fill-up.
• The trouble code P0455 (Evaporative Emission System Leak Detected) pointed to a large leak in the gas system.

Suggestions from the Community:

• Many mechanics suggested checking the purge valve, suspecting it might be stuck open.
• Some recommended looking into an updated fuel cap and ensuring there was no contamination in the gas tank.
• Others thought there might be an issue with the gas tank valves, causing flooding during refills.
• The general consensus was that the purge valve was likely causing the problem.

Final Fix:
Even though the old purge solenoid didn’t show any signs of damage, replacing it resolved the issue.

Case #3: Kia

Vehicle Information:
2011 Kia Soul
Engine: 2.0L

Issue + Repair History:

• The MIL (Malfunction Indicator Lamp) was on, with the trouble code P0455 (Evaporative Emission System Leak Detected – Large Leak).
• The canister close valve was tested and seemed fine, but the problem persisted.

Suggestions from the Community:

• Some mechanics suggested that since the car was relatively new, it might still be under warranty, so it should be taken back to the dealer.
• There was a strong emphasis on the need for a smoke machine to effectively find leaks.
• Others warned against meddling with a new vehicle that might not be the technician’s responsibility.
• Some mentioned potential issues with the gas cap or the purge solenoid causing the code.
• It was suggested to clear the code and see if it returned after addressing possible causes.
• The importance of the gas cap clicking when tightened was highlighted, along with the possibility of a faulty cap.
• Overall, the consensus was that a dealer inspection covered by warranty would be the safest choice.

Final Fix:
The issue was resolved by replacing the purge control valve. The stuck-closed purge valve was preventing the system from creating a vacuum, which triggered the P0455 code.