Mercury Montego P0455: Meaning, Causes, + How to Fix

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P0455 in the Mercury Montego is a trouble code that indicates your truck has a LARGE evaporative emissions leak.

With this code, you shouldn’t notice any symptoms besides perhaps a noticeable fuel smell.

Mercury Montego P0455

P0455 usually is not an immediate threat to the driveability of your Montego. But, whenever the check engine light is on, it’s good to deal with the code as soon as possible.

Check that your Montego’s gas cap is present and sealing well.

Table of Contents

P0455 Definition: System Gross Leak – Evaporative Emission System

P0455 is a generic diagnostic trouble code, meaning it has the same definition for your Mercury Montego as any other vehicle.  Repair steps will vary depending on the model year and engine.

Evaporative Emissions System

P0455 Definition Mercury Montego
Purge valves come in many shapes and sizes

Your Montego’s EVAP system (Evaporative Emission Control System) helps reduce emissions from your car by collecting fuel vapors from the gas tank and sending them back into the engine for combustion. 

The EVAP system prevents harmful gases from escaping into the atmosphere and does not affect how the engine runs, which means this code is not a breakdown risk.

System Gross Leak

When there is a large leak in the Mercury Montego’s EVAP system, it will throw the P0455 OBDII Code.

P0455 indicates a large leak in the evaporative emission control system. (EVAP). There are different leak size codes. For example, P0456 means your Montego has a small EVAP leak.

While the trouble code may state that there is a “large leak” in the EVAP system of your Mercury Montego, the actual leak will most likely still look relatively small. The “large” really refers to how much pressure is lost.

Mercury Montego P0455 OBDII Code Symptoms

P0455 code will typically not be accompanied by any noticeable symptoms other than the smell of gas and the service engine soon light. You should particularly notice the smell of fuel around the fuel tank area or fuel filler tube.

The EVAP system deals directly with fuel vapors. If these vapors leak from the system, you’ll often smell them faintly while operating the vehicle.

Montego P0455 Trouble Code Causes

Here are the most common causes of P0455. How your Montego’s EVAP system works will depend on the model year and engine type.

  • Evap System Hose– The EVAP hose carries fuel vapor from the fuel tank to the intake manifold can begin to leak. This will cause the P0455 code. Look for either a tear or in the hose. This is one of the most common issues that causes the code.
  • Purge Valve– One of the most common causes of the P0455 code is the vapor canister purge valve. An EVAP purge valve is a component of the EVAP system that allows fuel vapors to be released from the charcoal canister and sent back into the engine for combustion.
  • Faulty Charcoal Canister– An EVAP (Evaporative Emission Control System) charcoal canister plays a vital role in operating a car’s emissions system. The EVAP canister is filled with activated carbon, which helps reduce pollutants by trapping fuel vapors emitted from the gas tank and storing them until they can be burned off in the engine.
  • Fuel Tank Sending Unit– It is possible for the gasket that attaches the fuel sending unit to the gas tank to go bad. This can reduce tank pressure and throw the code.
  • Fuel Cap– A bad fuel cap can cause P0455. Often, you’ll get a message informing you that the fuel cap is off even when it is on. If you are getting that message, plus a P0455, it may save you a ton of time and money to replace the fuel cap and see if it goes away.
  • Fuel Filler Neck– There is often a gasket where the fuel filler neck connects with the gas tank. This gasket can dry out, especially with vehicles that spend their time in dry climates. When the fuel filler neck gasket dries out, the fuel tank can’t hold pressure anymore.

P0455 Diagnosis

P0455 Diagnosis

Diagnosis at Home

Before sending your Montego off for a thorough evaluation, you can do a few things.

  1. Inspect the EVAP system hoses for a leak.
  2. Check the seal on your Montego’s gas cap. This video is a fantastic resource on how to test your gas cap.
  3. Use your nose. Walk around your car. Smell around the gas cap, fuel filler neck, EVAP hoses, and anywhere else you can safely get your head. You’re looking for the smell of fuel.

How a Mechanic Diagnoses P0455

A mechanic has a wide range of instruments to aid in diagnosing the p0455 code in your Mercury Montego.

  • The mechanic will typically check to see if there are any other trouble codes. Additional trouble codes provide clues to the problem.
  • After ascertaining what trouble codes appear with the P0455, the mechanic will typically inspect the EVAP system. This includes the purge valve, line, and canister.
  • The mechanic will inspect the gas cap to ensure it can handle pressure if you are getting a warning that your gas cap is off, even when it’s on, replacing it will more than likely clear this code.
  • The fuel tank pressure will be checked and monitored.
  • After the checks and fixes listed above, the mechanic will perform two tests: (1) A smoke test (using a smoke machine). (2) They’ll use a scan tool to confirm that the EVAP vent solenoids and valves are operating correctly.

Here’s a pretty good video on diagnosing these leaks from Scotty Kilmer, if you are interested:

Most Common P0455 Fixes

Here are the most common Montego P0455 fixes:

  • Gas cap replacement
  • EVAP line replacement
  • Replace charcoal canister
  • Replace the fuel tank
  • Replacing a vent control valve/purge valve

P0455 in the Mercury Montego can often be found with your nose

Is P0455 a Serious Concern?

While P0455 will not cause your Montego’s engine to stop running, it should not be treated lightly. You could have a fuel leak. Pay extra attention to your tank level and make sure you are not leaking fuel. We recommend taking it in and dealing with it right away.