ECU evap test not running, won't pass inspection

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by ramthecowy, Nov 13, 2021.

  1. ramthecowy

    ramthecowy New Member

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    Hi all, back again with more niggling issues.
    The 08 Prius had a 12v battery failure over the summer, was replaced, not sure how thorough the Toyota techs were in clearing/resetting everything, or if it matters. I have no steady check engine code (P1121 intermittent but thats a known story).
    State inspection was this October and the car failed for just about everything but "Fuel system", "Engine misfire" and "Comprehensive component". Everything else was in Not Ready. Which makes no sense because I don't understand how they just turned the car on, plugged in an ECU reader and expected it to clear everything without driving it. I'm not sure what their test procedure is, or if they're pulling historical codes...? The same garage passed it 2 years ago so I'm lost there.
    So anyway they gave me another month and I drove around with my OBD reader and Torque up out of curiosity. Sure enough after driving for about 20 minutes everything does tick over to complete... except the fuel system. I looked around here and found one thread that said the procedure was:
    • No CEL/MIL
    • Difference between intake and coolant temp must be less than 13F/7C
    • Intake and coolant temps start between 40F-95F/4.4-35C
    • Plug in OBD
    • Unscrew fuel tank cap to release pressure, screw back on
    • Start engine, get up to 50mph, (up to 65), maintain minimum for 15min
    Is this accurate? Any advice or tips?
     
  2. mr_guy_mann

    mr_guy_mann Senior Member

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    If your EVAP monitor is the only thing NOT complete or READY, then you are fine to go back for inspection. (at least in Jersey)- Every car that's 2001 and newer is allowed to have one monitor incomplete and still pass as long as there are no active codes and MIL is off but functions properly.

    That said, if codes were cleared then just drive the car- EVAP can be difficult to complete. It can take weeks to run or might not run at all in low ambient temperatures.
    From the manual:
    EVAP MONITOR (KEY OFF TYPE)
    (a) Preconditions
    The monitor will not run unless:
    – The fuel tank is less than 90% full.
    – The altitude is less than 8,000 ft (2,450 m).
    – The vehicle is stationary.
    – The engine coolant temperature is 4.4 to 35°C
    (40 to 95°F).
    – The intake air temperature is 4.4 to 35°C (40 to
    95°F).
    – Vehicle was driven in an urban area (or on a
    freeway) for 10 minutes or more.
    (b) Monitor Conditions
    (1) Turn the power switch OFF and wait for 6 hours.
    HINT:
    Do not start the engine until checking Readiness
    Monitor status. If the engine is started, the step
    described above must be repeated.
    (c) Monitor Status
    (1) Connect the intelligent tester to the DLC3.
    (2) Turn the power switch ON (IG) and turn the
    tester ON.
    (3) Check the Readiness Monitor status displayed
    on the tester.

    Sounds simple enough and sometimes I have no problems at all.
    For some year Toyotas you can have Techstream (or a similar "advanced" scantool) run a self test on the EVAP system that will complete that monitor.
     
    #2 mr_guy_mann, Nov 15, 2021
    Last edited: Nov 15, 2021
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  3. ChapmanF

    ChapmanF Senior Member

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    As you can see sort of buried in those instructions, the actual EVAP monitor test doesn't run while you are driving. You have to do enough driving of the right kind to satisfy the preconditions, but then you also have to park and leave it alone. The EVAP monitor test runs around six hours after you park and turn the car off. (It is what's happening in the various "I went out in the garage late at night and why was my Prius humming?" threads around here.)

    It won't always be exactly six hours; it can depend on how long the temperatures/pressures take to fall from driving to ambient.
     
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  4. ramthecowy

    ramthecowy New Member

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    Thank you for the input! I am very surprised that it failed inspection then as I've definitely met these criteria many many times - basically my daily commute haha! Since the battery replacement I've driven 2500mi so I'm not sure what gives. It looks like the car resets its check counters every time it's powered on and off (based on what Torque says) and needs to be driven for the counters to flip (apart from Evap, clearly) so it appears the shop just plugged in an OBD reader right after startup and expected everything to be ready. :/ Kind of lost on what to do as the car is clearly capable of passing
     
  5. ChapmanF

    ChapmanF Senior Member

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    If it is losing monitor status when powered off, you might check for a problem in the B+ circuit powering the ECM's memory during power off.
     
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  6. ramthecowy

    ramthecowy New Member

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    Hmmm if that were the case wouldn't it manifest other issues too? I would imagine ECM memory does more than just readiness codes
     
  7. ChapmanF

    ChapmanF Senior Member

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    If your throttle body or injectors are very dirty you can notice hard starting if the ECM forgets its learned adjustments. If they're pretty much ok then you might not notice much. If it is forgetting after every drive, then it's never getting much chance to learn anything you would notice it forgetting.

    A normally-functioning Prius ECM does not forget its monitor status between drives.
     
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  8. ramthecowy

    ramthecowy New Member

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    Right, that makes sense. I can't particularly tell.
    Is this easy to check myself or am I better off taking it to a mechanic/dealer? Did some Googling and searching in PriusChat, and wasn't able to find anything that made sense.
     
    #8 ramthecowy, Nov 19, 2021
    Last edited: Nov 19, 2021
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  9. ChapmanF

    ChapmanF Senior Member

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    I would start with the wiring diagram (more info), find the circuit that supplies power to the ECM when the car is off, maybe find what fuse that circuit is on and look at that, then look at the voltage on that circuit at the ECM connector.
     
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  10. ramthecowy

    ramthecowy New Member

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    Actually I've remembered one thing. I did have a P1121 CEL that came on intermittently in the summer (post battery replacement) as the 3 way valve has done its due course. If the ECU mem didn't have power then it wouldn't have remembered getting that code would it? I remember checking with my OBD quite a while after the code appeared and it had stored a log of it.
     
  11. ChapmanF

    ChapmanF Senior Member

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    I am not sure of all the details of what is in volatile and what is in nonvolatile memory in the ECM.

    I am only suggesting things you might check if you were right in post #4 that the monitor status is being forgotten between power-ons, which is not typical behavior.
     
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  12. ramthecowy

    ramthecowy New Member

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    Quick update: in the silence I did in fact manage to get the car to pass inspection which is a huge relief :coffee:

    In speaking with a friend he pointed out that to test for 12v supply at power off to the ECU (i.e. terminal BATT) that I need to check pins 6 (and 5) on E7 in the ECU, which is here:
    [​IMG]
    (posting in this orientation as thats how the ECU is mounted, in case anyone else ends up in this situation)
    I am waiting to borrow a multimeter to check this, but I do really doubt that there is loss of power. The car remembers this:
    [​IMG]
    ...and remembers stuff like pending codes and historical codes. I can't seem to figure out what's really going on.
     
  13. ChapmanF

    ChapmanF Senior Member

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    Do you have access to Techstream? It's possible you could get more information using its readiness monitor utility (the one that lets you enter specific trouble codes and get the status back for their specific monitor tests).

    I used that a lot while I was trying to get rid of the permanent P0102 I had for a year or so.
     
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