Our check engine light is on. Gas cap possible problem?

Possible causes
- Missing or loose fuel cap
- Incorrect fuel filler cap used
- Fuel filler cap remains open or fails to close
- Foreign matter caught in fuel filler cap
- EVAP canister or fuel tank leaks
- EVAP system hose leaking
- Fuel tank leaking
What does this mean? Tech notes
The P0455 it's a very common code, because the code is set if the gas cap is loose or missing. Start by tighten the gas cap and clearing the code. In most cases the code can be clear by disconnecting the car battery for about 30 minutes.
What does this mean? When is the code detected?
Evaporative Emission System (EVAP) control system has a very large leak such as fuel filler cap fell off, EVAP control system does not operate properly.
Possible symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
- Possible a noticeable fuel odor caused by the release of fuel vapors
P0455 Mitsubishi Description
This diagnosis detects leaks in the Evaporative Emission System (EVAP) purge line using engine intake manifold vacuum. If pressure does not increase, the Engine Control Module (ECM) will check for leaks in the line between the fuel tank and EVAP canister purge volume control solenoid valve under the following vacuum test condition.
The vacuum cut valve bypass valve is opened to clear the line between the fuel tank and the EVAP canister purge volume control solenoid valve. The EVAP canister vent control valve will then be closed to shut the EVAP purge line off. The EVAP canister purge volume control solenoid valve is opened to depressurize the EVAP purge line using intake manifold vacuum. After this depressurization is implemented, the EVAP canister purge volume control solenoid valve will be closed.

Read more: http://engine-codes.com/p0455_mitsubishi.html#ixzz3NlVyARyX

Sorry, but there is no "sensor at the fuel cap". Therefore, there is no code that says "sensor at the fuel cap". There is, however, a Diagnostic Test Code (DTC) That indicates a possible problem with the fuel cap.
(HINT: When you want information on codes, it is usually wise to include the code number that you are getting - that way, it can be looked up, instead of GUESSING at what the problem is from a code description that some generic code reader is telling you..)
DTC P0457 is defined by SAE J2012 as "Evaporative Emission System Leak Detected (fuel cap loose/off)"

At this point, I am ASSUMING this is the code you got.

This DTC is set when the Powertrain Control Module (PCM) detects that there is an in-tank pressure drop that is more than 7in. H2O within 30 seconds directly after refueling, or there is excessive purge (fuel Vapor) flow more than .06 lbs. per minute. Possible causes are:
> Fuel filler cap not installed after refueling
> Fuel filler cap loose or cross-threaded

There are other malfunctions that can also cause this code to set, but it will be accompanied by other codes indicating other possible failures.
If there are no other Evaporative Emissions System codes present, then there is most likely a problem with the way your fuel cap was put on the last time you got fuel.

Check your fuel cap and make sure it is on correctly and is tight.

P0496 is not alisted code.
P0455 - Evaporative Emission Control System Leak Detected Gross Leak (fuel vapors)
Symptoms - Engine Light ON (or Service Engine Soon Warning Light)
- Possible a noticeable fuel odor caused by the release of fuel vapors Possible causes - Missing or loose fuel cap
- Incorrect fuel filler cap used
- Fuel filler cap remains open or fails to close
- Foreign matter caught in fuel filler cap
- EVAP canister or fuel tank leaks
- EVAP system hose leaking
- Fuel tank leaking

Hi, if the code was P0455, there are other possible reasons. The computer fuel tank pressure sensor has detected a leak which could also be in the vapor canister, or the hose from the canister to the purge valve, or the purge valve itself may be leaking. Please inspect the system for these leaks. I may be able to provide some pics of these parts if you tell me your model, year, and engine info.

Evaporative Emission Control System Leak Detected (no purge flow or large leak)
What does that mean? This indicates a fuel vapor leak or lack of purge flow in the EVAP control system. It means a large leak has been detected. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.
Symptoms You likely won't notice any drivability problems.
Causes A code p0455 most likely means one or more of the following has happened:

• A loose or improperly affixed gas cap
• A non-conforming gas cap (i.e. not factory/original brand)
• Other leak or damaged piece in EVAP system

Possible Solutions With a p0455, the most common repair is to:

• Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
• Otherwise, replace the gas cap, and/or
• Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary

Check this info about P0455 - Evaporative Emission Control System Leak Detected (no purge flow or large leak)

This indicates a fuel vapor leak or lack of purge flow in the EVAP control system. It means a large leak has been detected. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.

Symptoms: You likely won't notice any drivability problems.

Causes: A code p0455 most likely means one or more of the following has happened:
A loose or improperly affixed gas cap
A non-conforming gas cap (i.e. not factory/original brand)
Other leak or damaged piece in EVAP system

Possible Solutions: With a p0455, the most common repair is to:
Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
Otherwise, replace the gas cap, and/or
Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary


Check it and keep us updated.

P0456 = "Evaporative emission (EVAP) control system leak detected (very small leak)."

The code is pretty standard and has to do with emissions. Manufacturers these days have strict rules to emissions that the car puts out. So, this code relates to that. It is Evaporative Emission Control System Malfunction A code P0440 could mean one or more of the following has happened:

• The gas cap is not installed or working properly
• The purge solenoid has failed
• The canister is plugged and not working properly

P0440 EVAP System No Flow During Purge Possible Causes Setting Conditions

• Charcoal canister is loaded with fuel or moisture
• Fuel filler cap is loose, cross-threaded, damaged or wrong part
• Fuel tank, fuel filler neck or fuel sending unit 'O' ring is leaking
• Fuel tank pressure sensor is damaged, disconnected or it failed
• Fuel tank vapor line(s) is clogged, damaged or disconnected
• Purge valve vapor line is clogged, damaged, or disconnected
• Purge or vent solenoid power circuit is open (check the fuse)
• PCM has failed

So, basically if you drove around with the gas cap off, or something else has happened, then this code would come up.

I would disconnect battery for 1 minute, and reconnect and see if the warning light comes back on.

Just remember you might lose your radio code if you do this.

Let me know how it goes...
PLease vote if you liked this response.

The check engine light comes only when the computer control unit (called the PCM) senses a fault in the electronic controls of the engine and/or the emission system, there are about 200 possible faults (the gas cap is just one) that turn the light on, to know what has developed a problem you must have the system tested, this is called an OBD2 fault code test, Kragen and Autozone parts stores do this testing for free.

Code P0442 means Evaporative Emission Control System Leak Detected-(small leak). Most times that code is set if you removed the gas cap while the engine was running. If not, you could have a bad gas cap. It's minor in the grand scheme of things, but to be on the safe side, replace the gas cap, have the code cleared, and drive the car for a day or two. If the light stays off, problem solved.

P0455 - Evaporative Emission Control System Leak Detected (no purge flow or large leak)

What does that mean? This indicates a fuel vapor leak or lack of purge flow in the EVAP control system. It means a large leak has been detected. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.
Symptoms You likely won't notice any drivability problems.
Causes A code p0455 most likely means one or more of the following has happened:

• A loose or improperly affixed gas cap
• A non-conforming gas cap (i.e. not factory/original brand)
• Other leak or damaged piece in EVAP system

Possible Solutions With a p0455, the most common repair is to:

• Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
• Otherwise, replace the gas cap, and/or
• Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary