Error code C1391. New anti-lock brake system?

There certainly are independent mechanics who know how to do Toyota/Lexus hybrid brake systems.

There is not a hard requirement to go to a dealer, though that does happen a lot just because folks have a tough time finding independents- but they are out there, and they have all the manuals, tools & software needed for a successful repair.

Good luck!

 

There isn't any thing in the car called "the antilock brake system", so the first job is determining which actual thing you need. There are two that are the likeliest suspects for a C1391:



If the best the mechanic can do is guess, the odds favor it being the top one. When cost is no object, people sometimes choose to keep it simple and change both. Otherwise, the mechanic might try to isolate the fault to one or the other; there might be a hissing leak sound that can be pinned down with a mechanics' stethoscope.

The parts seem to be running 5 to 6 hundred dollars each, and replacing either one is a bit laborious.

 

it is around $3,000. at a dealer typically

 

The extended warranty was for 150,000 miles OR 10 years after delivery of the car, whichever comes first. So, your 2012 is past the 10-year limit.

 

Do you hear it while your foot is on the brake, or every 4 or so seconds even when you are not touching the brake?

You might be talking about the sound of the pump running, but a recording might be helpful, because that sound is not often described as a hiss; more often as kind of a rattlesnake or joy-buzzer sound, It sounds like a small electric motor spinning a small pump. The sound is faint from inside the car because the pump is out under the hood. If you are hearing it every 4 or so seconds, the system is way past bad; that interval is hours when the system is in good condition.

If, indeed, the pump is what you are hearing, then yes, it does indicate a fault in one of the pictured parts. It does not, however, pin down which one. The reason the pump has to run is that hydraulic pressure is not being held, and the leak responsible for that can be in either one of those parts. It is typically an internal leak, so you also cannot look for a telltale trail of brake fluid; it just ends up dribbling past one of the internal valves and back to the brake fluid reservoir.

The internal leak might make an actual faint hissing sound, too faint to hear except in those intervals when the pump isn't running, and even then too faint to hear without a stethoscope, if at all.

Because steel brake lines and brake fluid are good sound conductors, even a hiss picked up on a stethoscope might be picked up from both parts, and leave some careful listening and exercise of judgment to decide where it originates.

If that is inconclusive and you're willing to gamble, the odds do favor the top one of those two units, just because there are more little valves in it to possibly leak. When cost is no object, it may be simpler to just replace both units and call it a day. That's what Toyota dealers were instructed to do with cars within the warranty extension miles/years limit.

If the pump (located in the bottom one of those two units) has been running every 4 or so seconds for some time now, then it has been treated to, effectively, extra years of wear by now, even if the original problem's in the other unit.

 

There's a sound you'll typically hear when opening the driver's door, a mechanical buzz that goes on for about 10 seconds, if the car's been sitting for a good while (say overnight). That sound will also be heard occasionally while driving, when the car decides some pressure is dropping too much. With a new, properly functioning brake system the sound will be quite infrequent, say every 15~20 minutes. When the brake components are failing, the sound becomes more frequent, till every 30 seconds or so.