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P0440 code shortly after fill-up

Discussion in 'Generation 1 Prius Discussion' started by Classic_pri, Nov 10, 2010.

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  1. Classic_pri

    Classic_pri Former 2001 Prius 0wner

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    Hi folks,

    I've got a 2001 Prius with a minor but annoying problem. It pops a P0440 code from time to time, always shortly after the gas tank is filled. Driveability/fuel economy are unaffected, and no other codes are ever triggered.

    I checked for a cracked hose nipple on the "tank retainer", as posted by forum member kmc6566, but the unit on my car looked ok.

    Any thoughts with regard to why this code would show up with a full tank only? I'm not a fan of just throwing parts at a problem, but I'm thinking of replacing the gas cap to see if that's the problem.

    Thanks,

    Russ in Wisconsin
  2. justkyle

    justkyle New Member

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    Hate to ask the obvious, but are you tightening the gas cap until it clicks each time?
  3. Classic_pri

    Classic_pri Former 2001 Prius 0wner

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    Well, my wife drives the car mostly, but she's well aware of the implications of leaving the cap loose! So I would say yes, she tightens it fully. She also says she never tops off the tank, which can, I know, produce problems with the evaporative system.

    I've been giving this a little thought today, and am pondering that a full tank might increase vapor pressure in the evaporative circuitry. Maybe that's what triggers the error code.
  4. UGC

    UGC Member

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    Technical Description

    Evaporative Emission Control System Malfunction
    What does that mean?

    This indicates that a part of the EVAP control system is no longer fuctioning correctly. The EVAP system consists of many parts, including (but not limited to) the gas cap, fuel lines, carbon canister, purge valve, and other hoses. 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 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
    Possible Solutions

    With a P0440 OBD-II trouble code, diagnosis can be tricky at times. Here are some things to try:
    • Remove and reinstall the gas cap, clear the code, and drive for a day and see if the codes come back.
    • Inspect the EVAP system for cuts/holes in tubes/hoses
    • Inspect for damaged or disconnected hoses around the Evap purge solenoid
    • Check and/or replace the sensor
    • Check and/or replace the purge valve
    • Have a professional use a smoke machine to detect leaks
  5. 13Plug

    13Plug Active Member

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  6. justkyle

    justkyle New Member

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    Make Sure you're paid up on insurance first! :)

    If you still decide to do a smoke test yourself, make sure your spouse didn't take out a bazillion dollar life insurance policy on you first!
    :D

    sorry, couldn't resist...
  7. UGC

    UGC Member

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  8. Classic_pri

    Classic_pri Former 2001 Prius 0wner

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    Well, it seems that for the first time a 0440 code popped up yesterday with less than a full tank. So that throws out fuel level as a constant.

    I've crawled under the car and looked around. None of the hoses appear cracked. I did find a small hose clamp that had rusted to pieces, so I replaced that.

    The gasket inside the gas cap may have hardened some. I'd think it should be more pliable if it's supposed to provide an airtight seal.

    A well-known parts supplier in Arizona stocks just the gasket for the cap for $11, and if I order $40 worth of other stuff they ship for free. So I think I'll try swapping out the gasket first.

    I may have found the following manual pdf somewhere on priuschat -- if so, it's a great referral. It provides some helpful schematics explaining how the OBD-II evaporative emissions control system works.

    This is it: http://www.autoshop101.com/forms/Hybrid13.pdf

    Thanks for the responses. I'll advise if the fuel cap gasket does the trick.
  9. bwilson4web

    bwilson4web 03 and 10 Prius

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    The trouble areas, Volume I, pp. DI-83:
    • Hose or tube cracked, damaged or loose seal
    • Fuel tank cap
    • Vacuum hose cracked or damaged
    • Fuel tank cracked, holed or damaged
    • Charcoal canister damaged
    • Open or short in vapor pressur sensor circuit
    • Vapor pressure sensor
    • ECM (I would expect other problems)
    So how are you reading the code(s)? The reason I ask is many over the counter scanners only show one code or otherwise don't include all possible error codes.

    The diagnostic procedure asks what was the engine state when it throws the code:
    • engine running?
    • engine warmed up?
    • freeze frame data, if any
    They suggest that if the error happens in less than 200 seconds,"check the VSV for EVAP, charcoal canister and vapor pressure sensor."

    GOOD LUCK!
    Bob Wilson
  10. Classic_pri

    Classic_pri Former 2001 Prius 0wner

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    bwilson, my scanner is pretty long in the tooth -- it's an Actron CP9035. I fear it might miss some codes on late model cars, but the '01 Prius is only ODB-II car we own. It's pretty long in the tooth, too!

    I believe the codes have been triggered with the engine warmed up, traveling at highway speed. I can't be too exact because the CEL light has never come on while I was driving. My wife is pretty tuned into what her car is doing, though, and she tells me it's been coming on after she's been driving awhile.

    I've been digging around a little and discovered that the filler cap gasket is on the Toyota maintenance schedule. I can almost guarantee it's never been replaced -- we bought the car four years ago w/53K miles, and it now has 107K. The gasket does seem somewhat plasticized. I ordered one today, so we'll see in a few days whether that's the problem.
  11. bwilson4web

    bwilson4web 03 and 10 Prius

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    I'm sure you meant ISO-9141, KWP2000, as OBD-II is to more modern protocol. <grins>

    Your wife's description sounds like more than 200 seconds which points at a real leak, somewhere. (GACK) They can be pretty involved to locate.



    Thanks, I hadn't read this before and that could just be me missing a posting about it. This does make sense as Wisconsin gas is likely to have been a different mix of hydrocarbons, probably refined from Canadian stock versus Gulf of Mexico / Venezualian crude used for our gas or Texas where I'd bought mine.



    I bought our 2003 in 2005 with 49,300 miles and had to drive 800 miles back to Huntsville AL. It now has 133,000 miles but I'll check my seal next time I fill-up.

    Bob Wilson
  12. Classic_pri

    Classic_pri Former 2001 Prius 0wner

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    Just to follow up on this thread, I installed a fresh gasket on the fuel cap of our '01 Prius 12 days ago. The original turned out to have a large crack in it that wasn't easily visible with the gasket in place. We haven't seen the P0440 code return, so I'm thinking that was the problem.

    I've noticed that the cap needs a little more manual pressure to reinstall it now with the new gasket -- I imagine it's because the new rubber has more elasticity than the old one.
    2 people like this.
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