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Category: Check Engine Light Repair and Diagnostic Help

P0440 - P0455
The control module tests the evaporative emission (EVAP) system for a large leak. The control module monitors the fuel tank pressure (FTP) sensor signal to determine the EVAP system vacuum level. When the conditions for running are met, the control module commands the EVAP canister purge valve OPEN and the EVAP vent valve CLOSED .


This allows engine vacuum to enter the EVAP system. At a calibrated time, or vacuum level, the control module commands the EVAP canister purge valve closed, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum level. If the system is unable to achieve the calibrated vacuum level, or the vacuum level decreases too rapidly, P0440 DTC sets.


This DTC tests the evaporative emission (EVAP) system for a small leak. The control module monitors the fuel tank pressure (FTP) sensor signal to determine the vacuum decay rate. At an appropriate time, the control module turns the EVAP canister purge valve ON and the EVAP vent valve ON. This allows the engine to draw a vacuum on the EVAP system. At a calibrated time, or vacuum level, the control module turns the EVAP canister purge valve OFF, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum decay. If the control module detects a leak larger than a calibrated amount, P0442 DTC sets.


A large evap system leak causes a P0455. This can be cause by a stuck open vent valve, or a loose or faulty gas cap.


This DTC tests the evaporative emission (EVAP) system for a restricted or blocked EVAP vent path. The control module commands the EVAP canister purge solenoid Open and the EVAP canister vent solenoid Closed. This allows vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the control module commands the EVAP canister purge solenoid Closed and the EVAP canister vent solenoid Open. The control module monitors the fuel tank pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near 0 inches H2O in a calibrated time, P0446 DTC sets.


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Comments (8)
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  • Guest - singh

    replace purge control vale

  • Guest - jmlaurel

    the check engine light on my 2002 mazda protege5 is turning ON, its start last December 2015 . i when to canadian tire to check the problem. they diagnose using OBD 2 code reader and they found the code P0455, they try to have a smoke test and i pay $118 but they don't found the what it cause of CEL. so they just reset the code and they give me 100 days to observed if ever the problem will come back. after one (1) week the CEL came back same thing they just reset and aside from CEL i also encounter one problem everytime i take gas my car the gas pump will stop in 5 seconds and start over again and it will stop. now i go to my mechanic to check my big problem he told me the charcoal canister is defective which is cause to the CEL and he also replace the fuel-filler neck which causes when i take a gas on my car which cost me $441. after two of replacing the said parts the CEL is came back again. please help me to my problem and what really the causes of the check engine light.

  • Guest - Bekim

    Thanks the most helpful thing I read

  • Guest - RICHAR

    VERY GOOD INFO ON THIS SITE PLEASE KEEP IT GOING ON

  • Guest - Phil

    If you are experiencing this issue (440) on a GM 3800 v6 Supercharged that was recalled for warped valve cover oil leaks and fire hazard repair (or if that recall work was never done) then you have a chronic engine vacuum leak due to the open/leaking warped plastic front valve cover leak (which also leaks oil onto the manifold). If all of the plastic decorative fire-hazard bits were removed to evade the fire hazard and no seal repair was done or the seal goop repair has failed again this issue can return.<br /><br />It's not the fuel system, it's lousy vacuum, which can also affect ABS and brakes.

  • Guest - ed

    If any one can help with this problem please email me. Thank you. I need a inspection sticker or I got to take my Jeep off the road.

  • Guest - ed

    I have a 2001 Jeep Wrangler 4.0 liter. I have a an EVAP leak someware. It keeps giving me a code so I cant get a sticker. Large os small leak. I replaced everthing in Jeep but it still won't clear codes. What do I do now?

  • Guest - TechHeader

    In reply to: Guest - ed

    I have a 2001 Jeep Wrangler 4.0 liter. I have an evap leak somewhere. It keeps giving me a code so I can't get a sticker. Large or small leak, I replaced ever thing in jeep and still won't clear code. What do I do now. Help. help
    <br />
    If any one can help with this problem, please email me at browned5678@yahoo.com Thank you ASAP. I need a insp sticker or I have to take jeep off the road.
    <br /><br />You say you replaced everything. What exactly did you replace?