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    cbs4 New Member

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    On our 2006 Toyota Prius, the malfunction indicator lamp (MIL) is on solid, also known as the check engine light. The car is only 1 year, 2 months old, and "only" has 46,000 miles.

    I'm headed to AutoZone after I type this to try and get a read out on what I assume to be an emissions related code, but in the meantime I'm wondering if this is a common occurance among the Prius Chat user base (like HID headlights going out on the blink, literally).

    A search found a 2004 Prius owner with a MIL solidly on, and as the story unfolds, he was given an intriguing run around by the dealer, who first told him that it was the fuel filler pipe assembly part that needed to be replaced to the customer pay tune of $850.00.

    After he checked online here, as well as his Federal emissions warranty booklet, it turns out that the part in question may have been covered under the extended statutory emissions warranty.

    Once he presented this information to the dealership, the dealership immediately changed it's tune and said the problem was the intank fuel pump that needed to be replaced, which is specifically excluded from the emissions warranty.

    This kind of run around is just what I fear, and if possible, I could use some links to threads I may have missed where other 2004-2007 owners may have experienced a MIL, and what the root cause may have been, so I can narrow down the possibilities to the most likely cause.

    Thanks in advance.
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    ScottY New Member

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    Without the DTC code, there's no way to guess. Come back with the code, many members on PC can help.
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    Tempus Senior Member

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    First check that the Gas Cap is on tight.
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    galaxee mostly benevolent

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    MIL= big red triangle. CEL= check engine light. however, you're right, many CELs are caused by emissions related stuff. the guy at auto zone may or may not get a code with his tool, many of the proprietary hybrid codes are not accessible w/o toyota's scantool.

    it could be caused by a ton of different things. i wouldn't take someone else's experience and immediately assume it is also going to be what you experience. there are a whole lotta codes that trigger that light.
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    cbs4 New Member

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    <div class='quotetop'>QUOTE(Tempus @ Mar 6 2007, 07:07 PM) [snapback]401366[/snapback]</div>
    That was the first thing my wife checked. I probably would never have thought of it, but she drives the car, saw the light, read the manual, and checked the cap. It was on. She reported she was able to click it again, but I pointed out that one can click it continually clockwise without further tightening it, so with that we assume the issue is not the gas cap.

    Since the light appeared, she has had about a dozen drive cycles, with the light remaining on. We are concerned about continuing to 40 drive cycles before having it looked at, but we are equally concerned about the integrity and practices of local dealers.
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    jimmyrose New Member

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    No way of knowing without having the codes read. I had this light (MIL) go on within a couple of days of picking the car up new from the dealership (@ 133 miles to be exact). It turned out to be a water bypass valve that was sticking (part of the engine cooling system). They replaced it, obviously at no charge, and that was the end of it. I would not recommend continuing to drive it; when they pull the codes, they will also be able to tell WHEN it went on, and your delay in addressing it might give them an "out"...

    Just a suggestion, you may want to poll the forum for trustworthy dealerships in your area.
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    john1701a Prius Guru

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    I've had mine come on twice. Both were easily traced back to a specific gas station... way too much of a coincidence for me to dismiss. Sadly though, I haven't used the experience as an excuse to purchase a ScanGauge. So I don't know what the code(s) were.

    All has been fine since then, perhaps because I've avoided that gas station.

    BTW: The second occurence I noted that the engine-light shut off upon immediately after the 4th restart. I assumed that's the normal "you've been notified of that event, so no need to show it anymore" interval.
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    cbs4 New Member

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    <div class='quotetop'>QUOTE(galaxee @ Mar 6 2007, 07:39 PM) [snapback]401380[/snapback]</div>
    As always, Galaxee, your input is greatly appreciated and highly valued.

    Not that it really matters that much, since it seems clear enough what light I'm talking about, and not that describing the light correctly will fix the problem, and not to distract from the main quest of this thread, but in order to best help Prius chatters help me, I did try to use the correct terminology from the start, figuring that this will also create value to the forum for others as a usable key word in a future search.

    Perhaps Toyota has changed the names of what the different problem indication lights are, but on page 128 of our 2006 Prius Owner's Manual*, the amber warning light fashioned in the shape of an engine is very clearly identified and described as the "Malfunction Indicator Lamp."

    I've also noticed that the MIL designation for the "check engine light" is consistent with the descriptions found in the pollution control laws of our state, as well as federal OBD-II regs.

    The big red triangle with an exclamation point inside that is unique to the Prius in our small fleet is also discussed on page 129 of the same 2006 manual, and is clearly identified and described as the "Master Warning Light." No reference is made of the Master Warning Light in any emissions control information I've read thus far, and in our specific case, the red triangle Master Warning Light has not illuminated recently.

    The red triangle did light up over a year ago, however, during the one and only time she ran out of gas in the first week of ownership. The tank has never gone below half without a refill since that time. The tank was greater than half when the amber check engine (what Toyota calls MIL in the manual) lamp went on.

    *Reference: Toyota Publication OM47520U, Part No. 01999-47520, Printed in Japan 01-0511-00


    <div class='quotetop'>QUOTE(galaxee @ Mar 6 2007, 07:39 PM) [snapback]401380[/snapback]</div>

    Using the AutoZone scan tool this evening, I found one code: P0304, Cylinder #4 Misfire detected.

    Now what should I do?
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    cbs4 New Member

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    <div class='quotetop'>QUOTE(ZenCruiser @ Mar 6 2007, 09:12 PM) [snapback]401448[/snapback]</div>

    Code P0304, Cylinder #4 Misfire Detected

    Good point about continuing to drive it. By drive cycles I meant starts and stops with a bit of driving inbetween. She noticed the light in the middle of the day, but had to continue on with her day in order to get home, making a number of stops along the way. We counted the total number of stops and restarts (with about 10 miles of driving between most of the restarts) as a "drive cycle".

    After arriving home, she discontinued using the car until I find out more information before we take it in, or before we determine the code is anomalous and clear it with the scan tool and carry on.

    We don't want to give the dealer any "outs", nor do we wish to make a small problem worse. We also don't want to get taken for a ride down ignorance lane without first exploring the experiences of others in similar predicaments.
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    galaxee mostly benevolent

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    hmm, i've always heard of the mil referred to as the triangle. but hey. like you said, not important in the big picture :p

    anyway, glad to hear the auto zone guy was able to pull a code for you. that definitely helps in the advice department- i can get DH's opinion on what to do next. does the car run ok? no stumbling or anything?
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    galaxee mostly benevolent

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    there are 3 things that cause a misfire: a lack of one of the 3 essential components of engine operation. spark, fuel, or compression.

    start with a set of spark plugs, it's the cheapest thing that could cause the problem. you can even change em yourself ;) just use a good set of iridium tipped plugs if you do, recommend using the toyota plugs but that's your call.

    did they clear the code? if so, and it came right back, you can also check the ignition coils. swap the one farthest on the driver's side (#4) with the one next to it. see if the code then moves to cylinder 3, P0303 code. if so, the coil is bad and that's covered under powertrain warranty.

    those are the most likely causes and the easiest to check. the next item to check would be injectors, if the code came back right away after clearing it.

    it's probably not a compression issue, to be honest. those pop up with abuse or show up within a few hundred miles brand new if from the factory that way.

    there's a good start for ya... good luck.
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    cbs4 New Member

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    After reading John1701a's description of how he narrowed down his MIL lights to two bad fuel purchases at a particular gas station, the injectors in our car started getting the guilty look.

    While we always buy Tier 1 gasoline (regular unleaded from Chevron) that supposedly is used by all the major car manufacturers to develop and pass emissions standards, I thought I might try an additional bottle of Techron additive, double dosage.

    I also wiggled and pressed in the wire harness connectors to each injector coil on the engine, noting that #4 is particularly difficult to get to without removing other parts from the top of the engine bay. Thanks galaxee, for pointing out that #4 is to the right, toward the driver.

    Since the code wasn't scheduled to go away by itself for another 30 drive cycles, I went ahead and cleared the code, and had my wife drive it the next day. I told her to drive it assertively, and not to baby it. Accelerate onto on ramps, etc, to let the injector cleaner do it's work with an adequately heated engine, since Prius engines can end up running cooler with the hybrid assist.

    No codes have reappeared since, and it has now been one week.

    I'm not drawing any conclusions from the coincidence of my adding a double dosage of Techron, wiggling and pressing in the coil harness connecters, and the non-reappearance of the code. I have read where the code could have been just an anamolous cold start stumble in winter weather.

    I've also read where misfires can occur from carbon build up on the intake valves, burnt exhaust valves, or valves that are out of adjustment (too tight... zero clearance of rocker arm lash). The injector cleaner and sustained top end temperatures might have evacuated some carbon build up, but there is no way for me to know that for certain.

    Without removing the valve cover, I have no way of knowing the conditions of the valves to this engine, but my understanding is that the valves need to be adjusted periodically.
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    galaxee mostly benevolent

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    eh, don't worry much about carbon buildup. it's not a common thing in a prius. we rebuilt a 97 camry engine a while back and it had 130k on it... maybe 1/32" of carbon buildup on the valve faces and nothing on contact surfaces. the prius uses the engine even less. if you use good gas, and it appears you do, this won't be an issue.

    just about the only way to burn exhaust valves is if your timing's out.

    valves typically loosen up from wear on the adjusters and the valvestem. seeing them tighten is pretty rare unless you're just walking away from a rebuild and the builder adjusted em too tight.

    unless it comes back, sounds like you're set for now. let's hope that's the last you see of it. ;)
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    hobbit Senior Member

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    With the direct-acting bucket lifters the Prius engine has, there
    aren't any rockers or adjusters. One would hope that the buckets
    and cams and valve stems wear at about the same rate as the valve
    seats, which would ideally wind up canceling out leading to zero
    change in valve clearance over the life of the engine.
    .
    To do the valves in this car you need a big stock of those little
    buckets, of various pre-machined thicknesses, and do a bunch of
    math from feeler-gauge measurements to pick out the right
    replacements.
    .
    Almost makes ya wish for hydraulic lifters again...
    .
    _H*
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    galaxee mostly benevolent

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    yep, the buckets are used as adjusters on the prius. DH has a big box of em, along with the disc types for other engines, stashed away somewhere at work.

    you're right, there really should be no change in valve clearance at all. but if there was a change, it's more likely to loosen up rather than tighten up.
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    oldbettles New Member

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    Thank you...
    I had a friend warn about this but, it wasn't until I found what you had posted did it sink it.
    I checked the cap and it was on tight and clicking. I decided to take the cap off and then put it on, just because. And it worked...
    Up to that point there was no dash info and the power would not shut down.
    Thanks again:)
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    cwerdna Senior Member

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    bad combination meter?

    Holy thread resurrection! Assuming the brightness knob on the left side isn't turned all the way down and you're experiencing Luscious Garage | Blog | LG TV - Prius Dead Dashboard, then you have a bad combination meter. pEEf knows how to fix them for less than the amount listed there.

    If it happens again and you're still under warranty, try to take a video of it and get it fixed under warranty, ASAP, before your warranty runs out.

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