Passing State Inspection with P0456 (Evap)

Discussion in 'Gen 2 Prius Main Forum' started by Sung Woo, Nov 15, 2020.

  1. Sung Woo

    Sung Woo Junior Member

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    So...I've had the lovely P0456 for a while now. Like a year. The car drives fine, but it's time for inspection. Stupid me, I thought I could just reset it and take it over there. Needless to say, I failed due to all the emission sensors reporting "NOT READY".

    I drove around for a few days (about 60 miles total), and I got all the sensors but Evaporative Systems to switch from NOT READY to PASS. And then...I got the Check Engine light to flare up again.

    The fail code I've been getting is the infamous P0456. After a DTC reset, the car doesn't usually come up with another one until I get another tank of gas (about 250 miles of driving). So I'm hoping it'll be like this once again, but I'm beginning to wonder -- will the Evaporative Systems ever turn to PASS if I keep getting the P0456 on a regular basis?

    This is my 2007, BTW, with 205K miles.
     
  2. Elektroingenieur

    Elektroingenieur Senior Member

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    Probably not, since it sounds like the on-board diagnostic system is working just as the regulations require, to ensure that a vehicle with an emission-control malfunction can’t be made to pass an inspection by clearing the stored DTCs. The readiness monitor won’t complete until enough drive cycles have been accumulated to detect the problem, which if it still exists, causes the DTC to be stored.

    If you want to try to fix the problem yourself, see the P0455/P0456 procedure in the Repair Manual (more info). You’ll need a Toyota Techstream diagnostic system, or equivalent, to do the active tests.
     
  3. mr_guy_mann

    mr_guy_mann Senior Member

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    The emissions monitors just report whether or not the engine computer has run its tests. "Not ready" or "incomplete" means that it hasn't run and finished a particular test. "Ready", "complete" or "OK" means that it has run that test.

    If the tests run and find a fault, it will set a code (often a pending code for the 1st time, then a "normal" code with a check engine light on the second time).

    If you want the light to stay out you need to find and fix the problem. Could be a simple as a bad gas cap (I only use a Toyota part for this). It may be much more involved.

    Posted via the PriusChat mobile app.
     
  4. Sung Woo

    Sung Woo Junior Member

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    Thanks, guys. I have already done the gas cap switch and no dice. What exactly constitutes a drive cycle? If the check engine light comes on, say, after 60 miles of driving, and then doesn't come back on until another 250 miles, surely several drive cycles have completed by then?
     
  5. Elektroingenieur

    Elektroingenieur Senior Member

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    That’s from a preliminary edition of the Repair Manual for model year 2004. That edition is often useable for later models, but I couldn’t recommend it for this DTC, because of the changes Toyota made for model year 2006 and later, as New Car Features explains:

    “▶︎ ︎The construction of the EVAP (evaporative emission) control system has been changed. The VSV (for Canister Closed Valve) used on the ’05 models has been discontinued, and a canister pump module is used on the ’06 models.

    “▶︎ The EVAP service port provided on the ’05 models is removed from the ’06 models.

    “▶︎ Along with the change in the construction of the EVAP control system, some DTCs have been added and changed.”​

    The procedure in the PDF document has 23 steps; its equivalent in the Repair Manual for model year 2007 (RM03Q0U) has 35 steps, including references to several active tests not available before 2006.
     
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