Just bought a used Prius 2011 - Code P0171 and buzzing/barking brake

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by newguywithpups, Dec 2, 2019.

  1. newguywithpups

    newguywithpups New Member

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    Hi!

    New Prius owner here. Bought a used 2011 Prius with ~150k miles on it. Seemed to drive fine (and still seems to drive fine).

    Fewer than 50 miles in, the check engine light goes on. My OBD reader says it's a P0171, system too lean.

    Through some Googling, I do some more diagnostics and the car seems to have a constant long term fuel trim of +20-25%, both while running at idle (I tested in maintenance mode) and at higher RPMs like 1500-2500. Short-term fuel trims are pretty normal (under +/- 8%). Having driven it for 200+ miles already, I'm consistently getting around 41 mpg. That's on the low side, right?

    The Carfax shows the MAF sensor was replaced recently, so my guess is the previous owner tried to deal with this and decided to ditch the car. Not a good sign for me. Shortly after the sensor replacement, records show the PCV valve was replaced. I didn't research what that is or how it's related, but my guess is it was another attempt at fixing the issue.

    Also, not sure if this is normal, but when I was testing in maintenance mode, I steadily increase pressure on the gas and the engine RPMs increase steadily to about 1500 RPM. Then I keep increasing pressure and the RPMs hold... all the way almost until I'm flooring it, then when my foot is like 95% down, the RPMs shoot up to 2500+. It was pretty much impossible to hold the RPMs anywhere between 1500 and 2500. Eco mode was off.

    Also not sure if this is related (most likely not), but sometimes when I step kinda hard on the brake, there's a loud buzz/bark from the engine bay driver's side. Not a mechanical whirr or gentle buzz, but like a jarring BZZZZ or a very rough squeak. I think it might be happening just as I start to let off the brake.

    Should I just ditch the car and get another? :cry:

    Thanks for your help!
     
  2. tankyuong

    tankyuong Senior Member

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    Brake accumulator goin out expensive
     
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  3. bisco

    bisco cookie crumbler

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    check with dealer for extended warranty
     
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  4. Mendel Leisk

    Mendel Leisk Senior Member

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    Yeah there IS and extended warranty on the brake components on the firewall (two of them, the names elude me). Talk to your dealership service department, asap, see where you stand.

    Not sure. Just reading, could be MAF sensor or sensors in the Catalytic Converter?

    Better check the Exhaust Gas Recirculation and Intake Manifold (really part of EGR). Info:

    The simplest way to see where you're at, is to check the degree of carbon build up in the EGR pipe, a stainless steel connecting pipe between the EGR valve and intake manifold. Watch @NutzAboutBolts video #16 here:

    Nutz About Bolts Prius Maintenance Videos | PriusChat

    Two or three other videos linked there too, for the full cleaning of the intake manifold, full EGR clean, and Oil Catch Can install.

    Good thread:

    EGR & Intake Manifold Clean Results | PriusChat

    Another:

    Oil Catch Can, Eliminate that knock! | PriusChat

    Some tools worth having:

    E8 Torx socket (mandatory)
    E6 Torx socket (optional, but good to have, to remove the throttle body studs from intake manifold)
    3/8" ratchet wrench, regular and long handle, flex head, you can never have enough (or 1/2 plus reducer)
    1/4" ratchet wrench, or 3/8" to 1/4" reducer
    Ratchet extensions: you can never have enough
    Long needle nose piers, straight and bent tip
    Ratcheting 12mm box wrench (optional, but makes disconnection of the EGR cooler from exhaust easier)
    Torque wrench (3/8" and 1/4" both good to have)
    Floor jack and safety stands (or ramps): basically some method to raise front, if you need to take underpanel off, which you may need to, both for access and to recover dropped items.
     
    #4 Mendel Leisk, Dec 3, 2019
    Last edited: Dec 3, 2019
  5. ChapmanF

    ChapmanF Senior Member

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    Seriously, the barking brake noise? Check the firmware version installed in the brake ECU, compare to the right one listed in T-SB-0363-10 (for the correct wheel size). Worry about other repairs only if the firmware is already that new, or if upgrading it doesn't make the bark go away.

    A P0171 code and maxed-out fuel trim are likely to mean just what you'd think, that not enough fuel is being delivered. Wouldn't hurt to check the injectors and the fuel pump delivery pressure.
     
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  6. newguywithpups

    newguywithpups New Member

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    Cool - just bought a $20 Techstream cable off eBay. Will figure out how to do the firmware doohicky.

    I'll take the car to an actual real car person and hopefully they can figure out what the deal is for the P0171.
     
  7. newguywithpups

    newguywithpups New Member

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    K, if the firmware thingy doesn't work out, I'll check about the warranty. Long shot but worth it. If it turns out to be the costly fix and I'll need to shoulder it, I'll probably just drive the car into the woods and let it out there... that or just put a bullet between the eyes... no need for it to suffer long costly repairs.... its ok shhhhh...


    According to Carfax, MAF sensors replaced like a month or two ago. My guess is that was previous owner's attempt at fixing the problem. Haven't considered the other sensors though...

    Thanks for all the other detailed info! I'll try to figure out what I'm down to try vs how much to rely on someone I can pay to try and troubleshoot.
     
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  8. Mendel Leisk

    Mendel Leisk Senior Member

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    Have you read "Christine"... :whistle:
     
  9. Grit

    Grit Senior Member

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    So the brakes actually goes "woof-woof-woof"? :barefoot:
     
  10. ChapmanF

    ChapmanF Senior Member

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    Some people have called it a quack. Some have called it a honk.

    AFAIR, no one has thought it sounded like a moo yet.
     
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  11. newguywithpups

    newguywithpups New Member

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    Took the car into a car place today. Car guy says brake noise is brake booster, but that it's not an immediate concern until I start getting some lights/codes, and that likely the squawking noise will get longer as the problem gets worse. I'll still try the firmware thing once my knockoff Techstream (I'll call it Techsteam) arrives. I have installed Windows 7 32-bit on an old laptop in preparation.

    As for the P0171, he says the fuel injectors (all 4) are open for ~5ms, longer than the usual 3+ ms. He says it's likely the injectors are clogged from using low grade fuel and that the car is trying to compensate by opening the injectors longer. His solution is to replace the fuel injectors.

    Any way I can look into this more? I wouldn't want to replace the fuel injectors if that's not the problem.

    How is fuel trim measured? Does something actually sense how much fuel is being delivered? Or is it possible that fuel trim is actually how much fuel is attempted at being delivered (thus meaning fuel trim is more of a control than a measurement)? Is it possible that at some point the O2 sensor in the exhaust properly sensed a lean mixture because of clogged injectors, then the car tries to compensate by increasing the injector time, which increased LTFT... and all that results in now delivering the proper amount of fuel (with a boosted LTFT measurement). And if that's the case... is there even a problem with this?
     
  12. ChapmanF

    ChapmanF Senior Member

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    The car has a "mass airflow sensor" upstream of the throttle body, telling the computer how much air is being drawn in. The computer knows what the right proportion of fuel to air needs to be for proper combustion, so it knows how much fuel to try to inject. After the combustion, downstream in the exhaust, it has an air/fuel ratio sensor telling it what is left over in the exhaust, which reveals whether the actual amount of fuel that went in was too little, too much, or just right. So the computer trims the injection timing accordingly. They call that "closed loop feedback", because the computer is able to control the inputs while measuring the actual results.

    The computer can trim the injection timing up to a maximum of around +25% if I remember right. That means you can still be driving around with the injectors about that bad, but beyond that it will seem to get worse quick.

    Still, if there's a sign the injectors are clogged (and a persistently high fuel trim is such a sign), you don't necessarily want to say "hey, the computer can adjust the trim, so no problem". The car really will run better with cleaner injectors. One reason is that the injectors don't have to all be clogged identically. In addition to being all some percent off from ideal flow, dirty ones can be substantially different from each other, and the computer can't trim them individually, because it doesn't have exhaust A/F ratio sensors for every cylinder, just the one in the manifold. You can see this history of an injector cleaning with before/after results for an example of how that goes.

    My experience there is with sending injectors to a specialized restoring service (in that case, Cruzin Performance in Michigan, but there are others) that does a thorough restoration with parts replaced and before/after test printouts, and that was coming in around $83 for a set of four at the time, and that's a considerable savings over just buying new injectors from Toyota.

    On the other hand, you'll see other PriusChatters are finding aftermarket or ebay injectors new for less than the cost of having old ones restored, and going that way. I tend to lean toward restoration, which results in still having Toyota OEM injectors, and they're clean and up to spec again, and you have the test results telling you what happened. But that's me.
     
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  13. newguywithpups

    newguywithpups New Member

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    Finally got my Techsteam in this past week. My car looks to already have the most current firmware for the brake ECU.

    Last time when I visited the car guy, he said the noise is not a concern unless I start seeing lights on the dash like ABS or whatnot.

    As for the lean system, I'll try to switch out the injectors myself sometime...
     
  14. ChapmanF

    ChapmanF Senior Member

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    If you know you have the right brake firmware version, and it still quacks/honks, and you happen on a nice day with some spare time, you could try a bleeding sequence and see if that improves anything. My guess about the quack/honk (after ruling out the firmware version) is some valve in the actuator acting like a saxophone reed while some gas-bubbly brake fluid goes through it.

    There are two bleed sequences; the longer one (for when there might be gas in the actuator) requires the wipers and cowl out, for access to a bleed screw on the stroke simulator.

    I have a (completely speculative and unproven) notion that certain not-much-warning brake events could result from a gas-in-the-hydraulics situation that develops slowly over time, without much in the way of symptoms while it's developing.
     
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  15. newguywithpups

    newguywithpups New Member

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    Thanks! I'll look up how to do this and try it when I switch out my spark plugs and fuel injectors (since that requires removal of the wipers and cowl).
     
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