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2009 Prius All Brake Lights on. No RR Brake

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Jirons, Jun 13, 2023.

  1. Jirons

    Jirons New Member

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    Hello All,
    Working on my brother's 2009 Toyota Prius with about 260,000 miles on it. iIt is experiencing some braking issues and I'm stumped.

    I'd say I'm pretty handy, been working on cars all my life, and I'm a mechanical engineer for Honda, but I just can't outsmart this car. Lol

    The brakes seemed to be very weak, long stopping distance, very bad pedal feel. So my brother and dad took the liberty of trying to bleed the right rear brake without using any tech stream software or anything. Now all of the brake lights are on, and the right rear brake is unresponsive. with the vehicle lifted up, and the pedal depressed the other 3 are locked and the rear right just spins free.

    I've gotten a copy of Toyota Techstream and looked for faults on the vehicle's computer. I've never used software like this, so if this isn't all of the info you need. please ask. but the faults on the vehicle are as follows;

    Engine and ECT
    P0420
    P0560
    ABS/VSC/TRAC
    C1242
    C1253
    C1256
    C1343
    C1377

    I thought there may be an issue with wheel speed sensors because the ABS tends to be driven based on wheel speed, so i took the car for a test drive and logged the wheel speed, and the voltage output from the pressure transducers on each corner, and found that all of the wheel speed sensors are working, but the pressure transducer for the RR reads a constant value the whole time. could be from no pressure, or a faulty sensor. But when the bleed screw is opened only a slow drip comes out.

    I have a 2004 Toyota Prius currently, it seems to be free of issues, except for the aftermarket sunroof installed by the previous owners. -_- So I can take some parts from that one to try on the 2009 if that is necessary for troubleshooting, but I still need to drive it.

    Any advice?
     
  2. Tombukt2

    Tombukt2 Senior Member

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    In the manual which is posted somewhere around here and I need to go fly I did find the piece of paper that I had that had this on there I just did my 2009 and didn't use any tech to believe and I own tech have it right here but I found this paper that said I could do it without it and one of the maneuvers to bleed the back brakes I think that's right you take the relays out or you take the relays out so you can bleed the front put the relays back in and if your front reservoir and everything is full when you crack the bleed screw on the rear brake fluid should come shooting out You should hear the pump come on and everything because if I'm not mistaken the rears are not connected to the pedal hydraulic system they're completely operated by the pump and accumulator Good luck buddy
     
  3. Jirons

    Jirons New Member

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    Doesnt seem to let any fluid out. Only a very slow drip when the bleed screws are taken out
     
  4. Tombukt2

    Tombukt2 Senior Member

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    Don't take bleed screws out You just crack them The back brakes should squirt fluid out of them I think the car has to be on etc etc I think they're always under pressure I can't remember exactly but when you do it you do the backs first You have relays out I think I have to go find the paper. And then brake fluid should squirt out the back like a rocket a pump pumps it out so maybe your pump is not working and so therefore you have no rear brakes this kind of happened when my accumulator pump assembly on my '09 went bad The lights were on for 2 years then finally one day only one caliper was working in the front the rest of the brakes were out step on the brake head towards a ditch if you weren't careful. Swapped it out and bled the brakes without tech and everything's been off and breaking fine ever since
     
  5. ChapmanF

    ChapmanF Senior Member

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    If the brakes were always under pressure it'd be hard for the car to move. :)

    The thing people notice is that (because there's an electric pump involved), you don't need to pump the brake pedal; you can just hold it pressed and get a steady stream out the bleeders. The pedal does have to be pressed though. A Brake Rock works.

    However, if the ECU controlling the brakes doesn't know you're doing a bleed, and it notices an unusual flow of fluid down a brake line, it can say "nope!" and valve off that line (so the system wouldn't lose all its fluid through a leaking brake line). That complicates matters.
     
    Brian1954 likes this.
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    I would clear yhe ABS codes then turn the car off and then go "ready" again- see if any codes reset.

    Some of those codes point to problems with the pump in the ABS unit, or power supply wiring to the ABS system.

    Listen to car while it's ready. Normally if you step on the brakes a few times, the pump will run for a bit (10-20 seconds?) then stop. Sounds something like a humming metallic rattlesnake.

    If you use Techstream and look at ABS data, you should see ACC (accumulator) pressure voltage. The pump should turn on when it goes down to around 3.1V and turn off around 3.6V.

    The pump should stay off until you use the brakes again a few times. If the pump runs continuously or runs every so often when not using the brakes, then something is wrong.

    Techstream has a function in ABS to bleed a single corner of the hydraulic system. Put a battery charger on the 12V (because the car has to be in "ignition on" mode - not "ready" and the 12V can get discharged). Follow the instructions on Techstream- but I suggest first confirming whether you have a fault with the pump-actuator unit or wiring.

    Posted via the PriusChat mobile app.