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C1256 low pressure accumulator- ABS beep

Discussion in 'Generation 1 Prius Discussion' started by Egbert, Mar 28, 2010.

  1. Egbert

    Egbert New Member

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    The brakes of my prius are in FAIL SAFE mode as there seems to be no pressure.

    The motor of the pump does run when ignition is set to ON. After clearing the codes - reset of the system - ABS light is off, but after a little while it detects the low pressure again.

    It seems to be the pump or accumulator.... Anyone knows a way of testing before i replace this expensive part?
     
  2. V8Cobrakid

    V8Cobrakid Green Handyman

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    this may be off topic... in my Gen II i had similar errors when an ignition coil went out... at first it had 0 effect on the engine. after a couple months, the cylinder stopped firing (rough idle). once i replaced the coil, everything turned back to normal...

    beyond that... i'm not sure.. there are a handful of people here who would probably know more about your gen I prius...
     
  3. Egbert

    Egbert New Member

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    I can't imagine that in my case this would be a cause.... As even when in stand ON ( engine not running ) this low pressure is detected over and over again after system reset / clear codes.

    Think i am going to try to find a used pump/acc .....

    The Toyota dealer is not af any great help. They do have the manuals but there is no mechanic that has this knowledge right now.
     
  4. bwilson4web

    bwilson4web BMW i3 and Model 3

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    First check the power circuits going to the hydraulic booster:

    • 40A ABS NO. 1 - first fuse
    • 20A ABS NO. 2 - second fuse
    • 30A ABS NO. 3 - third fuse
    • ABS SOL RELAY - relay to pass NO. 1 fuse current
    • HYBRID MTR NO 1 RELAY - relay to pass NO. 2 fuse current
    • HYBRID MTR NO 2 RELAY - relay to pass NO. 3 fuse current
    It looks like these fuses and relays are found in all three fuse boxes in the engine compartment. You might want to test the relays on the bench to make sure these relatively low cost parts haven't failed.

    Did this happen while driving or when you went out to start the car?

    Are there any other symptoms? Is the car drivable?

    Bob Wilson
     
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  5. Egbert

    Egbert New Member

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    Bob,

    I think fuses are OK as the pump does run sometimes. After a reset of the codes it runs for 10 sec. I can hear it a little bit and i can feel it trembling. After the car detects an error it goes on for 1 sec. every 5 seconds.

    The brake pedal is ROCK HARD. When i clear the codes and put the car in ON while
    pressing the brake pedal it goes down a little.

    The pump does build up some pressure, but too little

    I can drive the car. No rear brakes at all and i must press very very hard to make
    it stop. It is not really safe to drive

    --> I will check the fuses however to be sure!
     
  6. Egbert

    Egbert New Member

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    Why does the pump have a Low Pressure and a High Pressure switch? I have a few pages of the Toyota hand book here.

    Or is this just fail over? To be able to detect the pressure from 2 different sensors?
     
  7. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Owch! This sounds bad (expensive too.)

    The cheap fixes are to find a failed fuse, relay or loose connector. But once we get into the ABS brake systems, I'm not comfortable with trying to figure out the specific failure mechanism. I'm interested but gosh darn, stopping is pretty important.

    Do you have pages DI-434 to DI-439 covering diagnosis of the C1256 code?

    Their "trouble area" list:

    • Accumulator
    • Pressure switch
    • Hydraulic brake booster pump motor
    They test the accumulator operation with a high pressure gauge at the rear wheels (North American models have rear drum brakes) at 5,099-8,924 kPa. The hydraulic motor is tested by jumpering the battery to the motor leads and listening for it running. The rest of the tests involve measuring the two, pressure switch resistance changes.

    If someone has the "New Car Features" for the NHW11 covering the brakes, it should include a reasonable, operational scenario about how the brakes work. But that doesn't seem to be part of the maintenance manuals.

    Bob Wilson
     
  8. Egbert

    Egbert New Member

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    Bob,

    I have pages DI-381 to DI-386. Seems to cover the same topic. As the system goes in FAIL OVER the valves are closed so that no pressure will go to the rear brakes.

    I think i should measure the changes in resistance of the pressure sensors while jumpering the battery to the pump and see if it changes enough. Read something of
    5 kohm to 0 kohm ...

    For that i have to remove quite some parts ... you can't reach it very well .....

    Can you give me an idea of how powerfull this running of the pump can be felt. I think it is quite gentle .. too gentle .. the average fuel pomp is more noisy ...

    Maybe there is air in the system? I can bleed the front brakes, but as there is no pressure at all at the rear brakes i can't bleed the whole system. The valves in the ABS block are probably closed ...
     
  9. Egbert

    Egbert New Member

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    Do you happen to have more information about the pump and the accumulator? Is the relief valve electronic or mechanic?
     
  10. bwilson4web

    bwilson4web BMW i3 and Model 3

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    I wish I could help more but we're "on the same page" but you have the broken car. Sad to say, you're at the 'bleeding edge' unless someone else has anything to contribute.

    Bob Wilson
     
  11. jk450

    jk450 New Member

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    Did anyone bleed the brakes or work on the brake system in any way just before this happened?
     
  12. Egbert

    Egbert New Member

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    I read something about bleeding the hydraulic pump .... is this procedure for bleeding brakes
    identical to that of the prius II ??
     
  13. bwilson4web

    bwilson4web BMW i3 and Model 3

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    I don't know since I don't have an NHW20 maintenance manual. Regardless, this is a synopsis of pages BR-4 through BR-6. Here are some of the warnings:

    • brake fluid attacks painted surfaces
    • with the cap off, fluid will spray when pressing pedal (coating inside of engine compartment?)
    The steps are:

    1. Fill with SAE J1703 or FMVSS NO. 116 DOT3
    2. Release pressure from power supply system
      1. turn ignition switch OFF, press brake pedal more than 40 times
      2. turn ignition switch ON, check that the pump stops after 30-40 seconds
      3. If pump does not stop, refill reservoir and repeat steps 1-2
    3. Turn ignition switch off, bleed right and left front brake caliper by depressing brake pedal 20 times or more (NOTE: I did not see a bleed valve indicated in the instructions or a sketch ... however page BR-26 shows a bleeder plug on the inside of the caliper, torque 8.3 Nm)
      1. Turn the ignition switch ON, check that pump stops.
    4. (NOTE: North American NHW11 have rear drum brakes) Fully open the bleeder plug on the right or left rear brake cylinder and drain fluid while depressing pedal for 3 seconds.
      1. Perform bleeding on first one side and then the other.
      2. Not necessary to repeated press the pedal as the fluid flows out on first push
    5. Turn on ignition switch from time to time to check that the pump stops. Make sure plenty of fluid in reservoir but keep cap on so it won't spray.
    Now the next part is the most difficult:

    1. Connect TOYOTA hand-held tester
    2. Turn ignition switch ON and select "AIR BLEEDING"
    3. Holding the brake pedal depressed, turn SRRR solenoid ON with the tester for no more than 2 seconds
      1. It looks like SRRR is on pin 3 of brake actuator connector B2. I don't have a sketch of the connector, yet. It may be possible to jumper the SRRR solenoid.
    4. Turn SRRR solenoid OFF and release brake pedal
    5. Check that pump motor stops after 20 seconds
    6. Repeat 3 times
    7. Clear the DTC code
    8. Refill fluid in reservoir
    I would recommend heading over to the YahooGroup, "Prius Technical Stuff" and search for Hobbit's description of bleeding his NHW20 brakes. I suspect he had a similar set of challenges, not having a Toyota scanner to operate the brake solenoids. You may want to run this note past the experienced Prius owners at "Prius Technical Stuff".

    Did you find a leak or low brake fluid level?

    Bob Wilson
     
  14. jk450

    jk450 New Member

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    No, it's not.
     
  15. treet007

    treet007 Member

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    I recently had a second opinion on a potential brake problem with my 2002 Prius (145K miles). The first mechanic stated that the pads were wearing unevenly and there may be a possible caliper problem. This mechanic proposed to replace the pads, calipers, and rotars but he would not know until he took the brakes apart. However, the symptoms are not consistent for a caliper malfunction. The second opinion from a different mechanic (@ a different Toyota shop) stated that the brakes were fine.

    So, why am I posting this on this thread? Because the symptom relates to a possible hydraulic booster problem, and the hydraulic booster comes in a kit for the brakes. $1100 + $660 labor. However, since we have no codes or any warnings, we are going to "wait and see".

    Symptom: when you press on the brake, the car takes a lot longer to stop. This does not occur often. It can occur once a week or so, but it is not consistent. So the hydraulic pump may not be providing enough pressure periodically, but the problem is not enough to show any codes (in my case).

    There are no TIDs related to this, but the mechanic (from the 2nd shop) found out from his contact at Toyota that the region has 10 kits in their inventory for the 2001-2003 Prius. So may be a recall or TID may occur related to the hydraulic brake booster? Anyone know anything else about this?
     
  16. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Perhaps you might turn the wheels all the way to one side, take a photo of the brakes on each side and then turn the wheels all the way to the other side and again take photos. This would at least give us some empirical data instead of taking the side of one or the other mechanic.

    If you are fairly near Sanford NC, you might give Taylor Automotive a call, 919-774-4037, and see if they can look at your brakes.

    Bob Wilson
     
  17. treet007

    treet007 Member

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    Sorry for the delay. My sister-in-law works second shift and I can only get to the Prius on a limited time. I did try to take the photos, but they were the back side. You can see the boot, but not much else. Do you want me to instead remove the wheels and take the photos?
     
  18. classic prius

    classic prius New Member

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    See classicprius.com for a description of a similar experience gone wrong. There are photos of the parts in question in the Brakes sections.
     
  19. FireFighterHill

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    Can anyone provide me a part number for the ABS SOL RELAY? Im not sure mine even has one or is supposed to. There is a spot for one next to the HYBRID MTR NO 2 RELAY, but its empty.
     
  20. ChapmanF

    ChapmanF Senior Member

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    Are you talking about the relay box mounted on the cowl above the engine, and did you type HYBRID when you meant HYDRO MTR NO.2?

    My 2001 wiring diagram shows that box as HYDRO MTR NO.1, HYDRO MTR NO.2, an unused socket, and IGCT Relay (passenger side to driver's side order).

    -Chap
     
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