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Intermittent brake issue.

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Kbagwell89, Jul 24, 2021.

  1. Kbagwell89

    Kbagwell89 New Member

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    2004 with 225100 miles, brakes intermittently feel like they are "letting go" when easing to a stop. No codes, no beeps, no random lights. Replaced front pads in March and front driver's side wheel bearing hub in April. I've read several posts on here but every one involved some sort of light/code. Any ideas appreciated.

    Posted via the PriusChat mobile app.
     
  2. bisco

    bisco cookie crumbler

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    that feeling is usually the transition to full friction braking around 6-7mph. rough, bumpy pavement can make it worse as the traction control kicks in
     
  3. Kbagwell89

    Kbagwell89 New Member

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    Does it well above 7mph. It's hard for me to explain, like it starts to brake and then suddenly its like the front brakes arent braking anymore and i have to put the pedal to floor to slow it down. Which makes it jerk/buck like someone learning to drive stick.

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  4. ChapmanF

    ChapmanF Senior Member

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    Is this a feeling you notice when gently easing to a stop and the road surface has a bump, pothole, manhole cover, or other irregularity?

    If so, standard Prius brake behavior. Here's the thread where it was explained to me a dozen years ago when I bought my first Prius.

    It seems like we're not doing as good a job these days explaining it to new owners, which is kind of unfortunate, because it's not as if the car's behavior has changed any, and it does have a way of startling new owners if they haven't been told about it. Going out to a road with some bumps or potholes and getting familiar with the way the system responds is still the best advice.
     
  5. Kbagwell89

    Kbagwell89 New Member

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    I've had the car for a bit so fairly used to what it normally does. The problem started recently and it occurs randomly, I can be coming to a stop, already stopped and moving a few feet forward, or simply slowing down, road conditions, pot holes, bumps and such don't seem influence it. Most initial searches suggested abs actuator, but there are no codes or lights indicating on the dash.

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  6. bisco

    bisco cookie crumbler

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    the actuator will often misbehave well before an event. i wouldn't risk my safety with a 17 year old car
     
  7. ChapmanF

    ChapmanF Senior Member

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    Have you noticed any changes in how often the pressure pump runs? Do you hear squishing or squirting noises when you gently apply the brakes, or barking/quacking noises when you release them?
     
  8. mr_guy_mann

    mr_guy_mann Senior Member

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    What can happen is if one of the ABS wheel speed sensors starts to go bad, it can put out a weird signal (usually at low speed) that the ecu interprets as wheel lockup, causing it to falsely activate the ABS. It can be so brief that it might not turn on the "ABS active " dash light. Add the "double whammy" of the Gen2 Prius not handling a-regen-to-ABS-stop transition very well and you get a funky feeling brake sensation.

    You might be able to see if there is WSS dropout on Techstream (does techstream have ABS engagement logs on the Gen2?). A diagnostic step would be to TEMPORARILY unplug one of the wheel speed sensors (that will disable ABS, don't know if that will also take regenerative braking offline or not). Then drive it (under good road conditions) and see if there is any affect on the symptom.

    Techstream is also great for viewing pressure and pump data for the actuator assembly.


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  9. ChapmanF

    ChapmanF Senior Member

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    ... and while we're singing the praises of Techstream, it also allows you to set a speed sensor check mode, which makes the error detection for speed sensors way more sensitive, so if you have any doubts about the speed sensors, a short little drive in the check mode ought to tell you if there's any issue there.

    The repair manual specifies to do a drive in the check mode to confirm the wheel sensors as the last step of any wheel bearing job, though the number of times I've seen anybody post on PriusChat about a bearing job and say they actually did that part, I think I can count on the fingers of one elbow.
     
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  10. Kbagwell89

    Kbagwell89 New Member

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    It's raining right now but when the weather is better I plan to record/upload a drive in case any of it's noises aren't normal.

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  11. Kbagwell89

    Kbagwell89 New Member

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    Definitely didn't check after the wheel bearing replacement I have noticed the speedometer is off just slightly when compared to gauges on my phone or the one the police set up on the side of the roads.

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  12. ChapmanF

    ChapmanF Senior Member

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    I think it's standard for the speedometer to read a smidgen high, so if that's all you're noticing, it probably doesn't indicate a speed sensor issue.
     
  13. Kbagwell89

    Kbagwell89 New Member

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    Naturally after I post about the problem it's been having for weeks, it just stops.

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  14. ChapmanF

    ChapmanF Senior Member

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    You embarrassed it.