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

Brake accumulator goin out expensive

 

check with dealer for extended warranty

 

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.

 

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.

 

Have you read "Christine"...

 

So the brakes actually goes "woof-woof-woof"?

 

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

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

 

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.

 

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.