Matching You with a Pre-Screened Smog Check Center You will Love
Free Online Smog Check Diagnosis
$500 Free Consumer Repair Assistance
Failed Emissions Test
How to Pass the Test
Who Else Wants To Pass the Smog Check
Which Type Should I Choose?
    Forum > Emissions Component > Question

Join the community and post your questions. Ask-A-Tech right now!

Emissions Component

How To Fix and Clear OBD-II Trouble Code P0455?

My car passed the smog check, and then the very next day, luckily might I add, the check engine light turned on. Two days later, the light went off. I went in to Autozone to see if a trouble code was stored, and in fact the parts guy said he read a P0455. Since then the engine light has come back on, but I haven't done anything about it. I'd like to know if this is serious and how i might be able to clear the P0455 code from the computer. The Autozone guy said it might have something to do with the gas cap... actually wanted to sell me a new gas cap to see if that would fix the problem, but I refused and thought to do some research on the matter first. Thank you.


OBD-II P0455 Trouble Code

Evaporative Emissions System Malfunction - Gross (Large) Leak Detected

Here is what P0455 means, in simple terms...

P0455 is a fairly straight forward OBD-II trouble code, in that it tells us that the engine computer has detected a large leak in the engine Evaporative Emissions Control (EVAP) system. The EVAP system prevents fuel vapors from escaping into the atmosphere. The system allows for fuel vapors from the gas tank to be absorbed by charcoal pellets located in the charcoal canister (also known as EVAP Canister), and to be released to the engine air intake manifold at a later time. The system is controlled by the engine control module (ECM) via a vent control and purge control valve. The vent control valve, when open, lets fresh air into the charcoal canister, purging the canister of fuel vapors and directing them to the intake manifold to be burned along side the engine's regular air/fuel mixture. Prior to the mandatory installation of engine EVAP systems in 1976, these harmful fuel vapors were released into the atmosphere.

What caused my vehicle to trigger a P0455 trouble code?

The ECM performs fuel vapor leak tests to ensure the EVAP system is functioning properly. The test occurs while your vehicle is being driven and also when your vehicle is parked (engine off). During the vapor leak test, the ECM commands the vent and purge control valves to close. The ECM then monitors the system for pressure/vacuum loss. If the ECM detects a leak, it records a trouble code. Large EVAP vapor leaks are recorded as trouble code P0455, while small leaks are recorded as trouble code P0456. Here are possible engine faults which may cause a P0455 trouble code to be recorded by the ECM (Listed in the order of expense to repair):

  • Gas cap left open or not closed tight enough
  • Defective gas cap (cracked) or damaged gas cap seal
  • Disconnected or cracked EVAP hose(s)
  • Defective or stuck-open vent control valve/solenoid
  • Defective or stuck open purge valve/solenoid
  • Damaged or cracked charcoal EVAP canister

What symptoms will my vehicle experience when trouble code P0455?

A P0455 trouble code will generally trigger the check engine light on. Depending on your vehicle's make, the check engine light may be referred to as the CEL, the Malfunction Indicator Lamp (MIL) or Service Engine Soon (SES) light. Freeze frame data containing information regarding engine sensor values at the time the ECM detected the P0455 fault will also be stored in the ECM's ROM memory and can be accessed via an OBD-II scan tool. Freeze frame data may be helpful to a technician when diagnosing the root cause of a P0455 trouble code when the fault is not easy to find.

  • Check engine light on
  • Fuel smell near gas tank filler neck, gas cap, engine compartment, and/or near charcoal canister
  • Decreased fuel economy
  • Incomplete EVAP system monitor

How can I fix a P0455 problem and where should I start?

First thing first... ensure your vehicle's gas cap is properly sealed. Make sure when closing the cap you hear the right number of clicks. If you found the gas cap to be loose or the gas cap's seal to be broken/brittle, then more than likely your problem is solved. Replace the cap with a new one or tighten the cap, depending on the problem you found, then drive your vehicle for the next few days as normal. The check engine light should turn off on its own and the trouble code erase from memory after a few drive cycles. A drive cycle is typically considered one full engine on and engine off cycle where the vehicle is driven for at least 30 miles and then parked for at least 8 hours. If you have access to a OBD-II scan tool, you can manually turn off the check engine light (erase the P0455 trouble code) and see if the check engine light will turn back on (over the course of a week or so of driving).

Should you find that the gas cap was tight and the seal appear to be in good condition, further diagnosis will be required. You will then need to inspect all EVAP hoses leading from the gas tank to the charcoal canister, and from the charcoal canister to the engine air intake (usually the air cleaner assembly). Finding the EVAP hoses may or may not be difficult. If you can locate the EVAP canister (usually near the gas tank), you can follow the hoses leading to the engine compartment and gas tank. Look for breaks and/or disconnections in the lines.

If the EVAP hoses too appear to be in good condition, not loose and not disconnected, the next step will require the use of proper diagnostic tools, and best left to a technician to handle. Typically to find a fuel vapor leak, a smog technician would test the entire EVAP system using an OBD-II scan tool and smoke machine. The smoke machine places smoke in the EVAP system. Leaks can then be visually detected. Diagnosis may also require electrical testing of the purge valve and the vent control valve for proper operation.

  • Check gas cap for proper tightness
  • Check gas cap rubber seal for cracks
  • Check all EVAP hoses leading to and from the charcoal canister and air cleaner assembly
  • Diagnose both the purge and vent control valves/solenoids

Can I drive my vehicle with a P0455 trouble code and illuminated CEL?

You may drive your vehicle while trouble code P0455 is present unless the gas vapor odors are very strong or you see obvious fuel (liquid) leaks. Extreme danger, seek repairs if either of these two scenarios exist. Note, a large fuel vapor leak may cause fuel economy issues. It is best not to ignore the problem, rather investigate the issue(s) as soon as possible.

posted by SmogTips Support 08-29-2018 05:46 PM

Related P0455 questions and answers you might find useful:

How To Fix and Clear OBD-II Trouble Code P0455? by paula on 08-29-2018 12:04 PM

Can I Pass The Smog Check With One Trouble Code? by Tom on 05-01-2017 02:45 PM

2001 Dodge Ram 1500 Failed P0442 and P0455 by Rafael on 11-19-2016 05:26 PM

BMW 328i P0420 and EVAP System Leak by Mark on 12-22-2015 02:15 PM

2002 Dodge Neon Trouble Code P0442 and P0455 Fix by Dianne on 11-19-2014 08:54 PM