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Brake failure with code C1365

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Jim Caldwell, Jan 7, 2016.

  1. Jim Caldwell

    Jim Caldwell Member

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    2014 Prius
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    IV
    Its a 2009 with about 75K miles. Back last year my wife drove through some thick mud, and this caused brake failure....yellow exclamation mark, VSC, and red brake warn lights all on and the buzzer sounding. I did not have mini VCI/ techstream at the time, but I went to car wash and sprayed out the insides of wheels heavily, and then did the jumper trick while pumping brakes 8 times, and the faults cleared and brakes worked perfectly for some months--- until this weekend. We had very heavy rain again, and the tires were encased heavily in mud again. I figured it must be a wheel speed sensor signal problem again. So I took it to car wash to clean inside of wheels. Now I have the mini-VCI /techstream running on a laptop to check it out. I ran the health check and it came back with code C1365 for the ABS/ braking system. I cleared all DTCs, and the fault lights cleared, but the brakes soon failed again with the same dash indications. Tried once more, same thing. Then I remembered about the trick last year of jumpering the diagnostic connector. This temporarily clears the fault, letting the brakes work fine, until the next time you start the car. Then it comes back. I clicked on that fault code in techstream, and noted that code C1365 was telling me that the accumulator press. sensor voltage was below threshold. Should been at least 4.7 volts, but it was at 4.37.
    But the brakes work perfect as long as you don't shut it down! So how can a part really be bad? If it is indeed bad as the code says, is this sensor replaceable by itself, or does the whole accumulator have to be replaced? Is it a job a DIY mechanic can do? I am able to at least drive the car, although my wife can't. I just stick two pins in the diagnostic connector, and I connect them temporarily with a jumper to do the reset trick before each drive.

    About a week before I replaced the RH brake pad, for the past few thousand miles I have been hearing an intermittent scraping sound from the RH front side when I braked. (Seems like its probably something unrelated to the current failure problem.) But the pad was perfect, hardly any wear, and there was no sign of anything on the wheel scraping. And still, when the brake system is working properly, I occasionally hear this scraping noise. Its baffling. I had to open the bleed valve and let a little fluid out in order to get the caliper back on the rotor, but the car was driven for about a week, perhaps 400 miles, before the day of the big rainstorm, and only then did the brakes fail.
    Should I check for 13.8V at battery? But wouldn't low batt. voltage cause other faults?
     
  2. ChapmanF

    ChapmanF Senior Member

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    Hi Jim,

    It can be very natural to draw inferences like "I drove through some mud, then X happened, so X was because of the mud" but it can also steer you wrong, waste your time, and risk your safety. In your case you could have cut out a bunch of time last year if you had looked up in the repair manual the chart of which brake system problems cause the light and the buzzer. That is limited to just a handful of severe problems, and wheels sensors aren't among them, but accumulator underpressure is.

    Bear in mind that the computer is stuck in a box, and when it sees a low reading from the pressure sensor, it has no way to climb out of its box and investigate why that is. But, you know, they didn't put the buzzer there to tell you a voltage was 4.37 instead of 4.7. They put the buzzer there because that voltage comes from a sensor that measures your brake fluid pressure, and that pressure is what stops your car, and they think you ought to know about that.

    Whether the pressure is actually right at those times and only the sensor or wiring are flaky, or the sensor is telling the truth at those times and the pressure is low, the computer can't get out of its box to find out for you. If you say it also felt at those times as if braking was impaired, that would suggest the sensor wasn't lying. If the pressure was low, whether that's because of mechanical wear in the pump or relief valve, or electrical problems in the circuits and relays running the pump, those are also questions on your list to answer. Toyota did actually build in enough electrical sense paths for the computer to give you a bit of help with that (though you still have to finish the diagnosis yourself); you'll want to see the exact troubleshooting steps on the repair manual pages for the specific code you're getting.

    -Chap
     
  3. PapaWill

    PapaWill Member

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    Jim Caldwell, I am having this code C1365 as well... Did you manage to get it fixed without going to the dealer? I would love to have some help here! Thank YOU!