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Causes, Symptoms, Severity and Cost

1992 mazda 929 sedan base fq oem 1 500

1992 Mazda 929

Technical Description:

Detection of a gross or very large leak in the Evaporative Emission System.

What P0455 really means:

The Evaporative Emission System is designed to prevent gasoline vapors from escaping into the atmosphere, and is built around a series of valves, rubber hoses, and a charcoal canister meant to collect vapors as they build up. These vapors are then systematically sent to the engine to be burned off. The computer regularly checks for leaks within this system, either by pumping in air, or by pulling a vacuum, and measuring the time it takes to reach a certain level. When a leak is detected the computer will command the check engine light on and set a P0440, which designates a problem in the system, and another code, such as P0455, to describe the size of leak.

What causes a P0455 code?

These are not very size-able leaks, even though the language suggests otherwise. The computer will turn on the check engine light for a leak as little as .020”, and will set the P0455 for anything.040” or greater. Remember that most of this system sits underneath the car commonly next to the gas tank, so it is exposed to the elements, especially the road grime and wetness that gets kicked up by the tires. The rubber hose will dry up and crack over time creating these small leaks, sand and moisture will get into the system and either rust up or jam the valves, and the gas tank and in particular the filler neck will just plain rust for ones made out of metal. These leaks will happen and it’s not your fault.

What is the severity of a P0455 code?

Minor (unless the car is noticeably running poorly). In other words there is no immediate reason the car will break down and leave you stranded.

What repair(s) are needed to resolve a P0455 code?

The gross leak P0455 is much easier to diagnose than smaller leaks in the system, so in some cases the diagnosis will be not be as long or costly. Outside of the gas cap not being on, the most common headaches here are the valves that open and close (they get stuck), the charcoal canister (gets a size-able crack), or the filler neck (rusts through).

What will it cost to resolve a P0445 code?

  • Estimated diagnostic cost = $100
  • Estimated part(s)+ labor cost = $25-600 (pending the type of repair needed)

Most shops will charge a diagnostic fee usually around $100. Unlike the smaller leaks which can require more diagnosing, the gross leak is found during that first phase. Because these leaks go beyond small pin holes in rubber hoses, the repairs can get costly. A missing gas cap might cost you $25, but to change a vent valve or purge valve, the price can run around $200 to $300 dollars, depending if the parts are available through the part store or the dealership. A charcoal canister will run $400 to $600 for repair depending on where it is located. To replace a filler neck the cost can run from $300 to $400.

Keep in mind, pricing will vary by location and your vehicle make and model. Save time and money by using Openbay to compare pricing and book an appointment with a service center in your area.

Service article written by an ASE Master Technician

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Common Service Intervals
Conventional oil change
Every 7,500 miles
Timing belt (Replace)
Every 105,000 miles
Air filter (Replace)
Every 30,000 miles
Spark plugs (Replace)
Every 30,000 miles
Rear differential fluid (Change)
Every 60,000 miles
Coolant (Flush/replace)
Every 30,000 miles
Hinges, locks & latches (Lubricate)
Every 7,500 miles

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