Brake actuator problem after replaced brake pipes

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Colin McEwan, Nov 18, 2022.

  1. Colin McEwan

    Colin McEwan Junior Member

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    Hi all,

    My 2007 Prius had a rear brake hose failure at the weekend, and since they quoted reasonably, I foolishly took it to the local Toyota dealership.

    (The symptoms were extended booster pump run, followed by VSC/ABS/Brake lights on, braking going into fallback hydraulic mode, a persistent continuous beep from the ECU and, diagnostically, a big puddle of brake fluid at the rear wheel. BUT, suspiciously, no fault codes over OBD)

    After replacing the hose, they said they couldn't contact the brake actuator ECU to bleed the rear brakes, and that the beeping sound (which they said they'd never heard before) was continuing. And they asked for £210 for 2 hours to "invetigate", which I stupidly said "yes" to without thinking about it more myself.

    So, is this likely to be a wiring fault (inability to connect to the ECU) or could the brake pipe failure somehow have precipitated a fault in the actuator ECU?

    And does anyone know if the hybrid system communication goes over the same CANbus wires that the OBD would be probing? If so that would make a simple wiring fault seem unlikely.

    Sigh.

    Thanks!
     
  2. ChapmanF

    ChapmanF Senior Member

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    The details are in the "multiplex communication" section of the New Car Features manual.

    Toyota Service Information and Where To Find It | PriusChat

    It's hard to give a short condensed version. A Gen 2 has one CAN, one BEAN (a Toyota proprietary network), one AVC-LAN (another proprietary one), and one gateway ECU that sits on all three. Diagrams in that NCF section show which ECUs sit on which networks.

    At the diagnostic connector, the CAN is accessible on the CANH and CANL pins. There is also ISO 9141 serial communication possible over the SIL pin with certain of the ECUs (including the skid ECU, which is also on the CAN). And there are some ECUs that monitor the Tc pin, Ts pin, or both.

    The dongle used to communicate with the car needs to be able to make use of all those pins, and the software (Techstream or some other app) needs to know which to use, and possibly other tricks like hopping through the gateway ECU, to be able to talk with all the ECUs in the car.
     
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  3. Colin McEwan

    Colin McEwan Junior Member

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    Turns out that, yes the CAN has a very intermittent connection, though the BEAN is still fine, and most signals are on the BEAN. The dealership got connection to the CAN by connecting directly to the ECU, and after some worries about the brake pump potentially being faulty, everything seems fine now except for the intermittent connection on the CAN. So I'll have to try and track that down at some point, but for the moment we have a functioning car again. Phew :)
     
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