1. Attachments are working again! Check out this thread for more details and to report any other bugs.

VSC, ABS, (!) and emergency brake light on, replaced 12v battery but still brake issues

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Prius_Aki, Apr 21, 2014.

  1. Prius_Aki

    Prius_Aki New Member

    Joined:
    Apr 21, 2014
    7
    0
    0
    Location:
    San Francisco Bay Area
    Vehicle:
    2009 Prius
    Model:
    N/A
    Hello,

    The other day while driving my 2009 Prius, the VSC, ABS, (!) and emergency brake lights popped on and the brakes got really squishy feeling. They basically, took longer to stop and when the car did start slowing down, it was like I was pumping the brakes, even though I wasn't. In searching through the forum, it seemed like the 12v battery was going bad and sure enough, the next time I checked it, the battery was completely dead (couldn't even start the car). I got the battery replaced and the car starts fine now, but the above lights are still on and the brake issue still remains (although it seems little better). It seems that the brake and battery issues are related, but can't find anything here (or anywhere) that addresses both of those. The car has 55k miles.

    Any assistance/suggestions would be highly appreciated. Thanks so much!
     
  2. JC91006

    JC91006 Senior Member

    Joined:
    Nov 10, 2013
    16,463
    8,377
    0
    Location:
    Los Angeles, CA
    Vehicle:
    2008 Prius
    Model:
    II
    You need to clear the skid control ECU DTC. Google that or search this forum and you will find some answers. More than likely, someone else will ring in with more detail instructions.
     
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,198
    6,461
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    1. Check the inverter coolant reservoir for fluid turbulence when the Prius is READY. If you do not see this then the inverter coolant pump has failed and needs to be replaced.

    2. Try clearing the skid control ECU DTC by using a jumper wire on pins 4 and 13 of the OBD-II connector. See posts 27 and 29 here:
    I'm in it now - Front wheel bearing/hub replacement | Page 2 | PriusChat

    and see post #7 here:
    How do you reset ABS light & yellow ((!)) ? | PriusChat

    3. If the above doesn't help and the braking system remains impaired, then you should immediately seek professional assistance. Or if you want to DIY further, buy Mini VCI (see Amazon.com) so that you can retrieve the DTC. This requires a Windows XP or Windows 7, 32 bit OS laptop. Good luck.
     
    Prius_Aki and cwerdna like this.
  4. Prius_Aki

    Prius_Aki New Member

    Joined:
    Apr 21, 2014
    7
    0
    0
    Location:
    San Francisco Bay Area
    Vehicle:
    2009 Prius
    Model:
    N/A
    JC, Patrick,

    Thanks so much for your suggestions. I did check the inverter coolant reservoir and there was turbulence. For those of you curious as to how this is exactly done (I didn't bother to open the cap the first time so missed it), you can see a video if you google the following:
    luscius garage & prius_code_p0a93_inverter_water_pump_seized

    If I understand correctly, clearing the skid control ECU DTC by itself would not address the underlying brake issue. Thus, it seems like I am out of easy options so, although I'm not looking forward to the minimum $170 diagnostics fee, I'll be taking it to a dealer tomorrow (unless anyone else has any thoughts). Really appreciate the quick feedback on my post though. I'll let you know how it turns out.
     
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,198
    6,461
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    You understand correctly.

    An alternative to paying the $170 diagnostics fee is to DIY by buying Mini VCI as I suggested above. However, once you have the DTC then you are still faced with the need to take some action. If you would not be comfortable repairing the brake system yourself, then you'd might as well go to the dealer now.
     
  6. Prius_Aki

    Prius_Aki New Member

    Joined:
    Apr 21, 2014
    7
    0
    0
    Location:
    San Francisco Bay Area
    Vehicle:
    2009 Prius
    Model:
    N/A
    Thanks Patrick! So the dealer says it's a bad skid control ECU. Wants to replace for $2,000 w/ labor. DTC is C1247.

    I asked why they didn't think it was the stroke sensor as you mentioned in another post. He didn't give a reason, just said he was sure it was the skid control ECU. Said they would have to cover it if it turns out not to be the issue.

    Looks like you can source these on the internet for a little cheaper. Is this a DYI type of job or leave it to the pros (I'm relatively handy in general but not necessarly "good" with cars specifically)?

    Also seems to be used ones for really cheap on eBay ($75). Risky? Thanks again.
     
  7. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,198
    6,461
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    The skid control ECU is located near the steering column. Access requires that you remove the steering wheel (including the driver airbag) and the instrument panel plastic trim (including the front passenger airbag).

    This is not an activity for the novice. You can obtain factory repair manual info at techinfo.toyota.com if you want to investigate what is involved.

    The manual shows the troubleshooting tree used to determine whether the brake stroke sensor is good or bad. The skid control ECU should be replaced only after all other causes have been eliminated, including the sensor and the wiring harness.

    For $170 you might think that the troubleshooting tree was followed. If the result of this was not documented on the repair invoice, then my guess is that once the DTC was retrieved, the tech specified the most costly repair.

    It is much easier and cheaper to replace the brake stroke sensor, located near the brake pedal assembly. That could be a novice-level project.

    For $75 it is quite reasonable to try a used skid control ECU vs. paying four-digits for a new ECU; assuming that you are game to do the needed instrument panel and steering wheel disassembly to get there.

    I also think you should clear the DTC now if that was not already done by the tech; and see how long it takes for the DTC to return. You may be able to get a few more months of service out of the car before the fault returns, giving you a chance to thoroughly consider your repair options.
     
    Prius_Aki likes this.
  8. SageBrush

    SageBrush Senior Member

    Joined:
    Jun 4, 2008
    11,627
    2,530
    8
    Location:
    Southwest Colorado
    Vehicle:
    2012 Prius v wagon
    Model:
    Two
    If the sensor is cheap I would be inclined to swap it out and hope the problem was fixed.
     
  9. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,198
    6,461
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
  10. nh7o

    nh7o Off grid since 1980

    Joined:
    Dec 10, 2011
    1,686
    337
    0
    Location:
    Hawaii
    Vehicle:
    2009 Prius
    Model:
    II
    Prius_Aki, where are you located? Please put that in your profile. There might be an independent shop willing to install a used skid ECU.
     
  11. Prius_Aki

    Prius_Aki New Member

    Joined:
    Apr 21, 2014
    7
    0
    0
    Location:
    San Francisco Bay Area
    Vehicle:
    2009 Prius
    Model:
    N/A
    Thanks all! Profile updated...SF Bay Area.

    Whew...I registered for techinfo and I don't think I'll be doing the installation myself. Really good to see the background information including the troubleshooting tree. I'll call the dealer tomorrow and see if I can get more information on what process they might have followed.

    Of course the warning lights are bothersome but the biggest problem is that braking does not work well. I can manage to drive it to/from the dealership, but wouldn't feel comfortable continuing to drive it daily as stopping distance is increased and/or unpredicable the way it currently is.

    Just curious, do you think a defective sensor could cause this underlying brake issue...and not just tripping the DTC? If so, I'd consider replacing the sensor myself first.

    BTW: $1,155 + shipping for the ECU is a few hundred less than what the current dealer is quoting for parts. Thanks for the reference.
     
  12. JC91006

    JC91006 Senior Member

    Joined:
    Nov 10, 2013
    16,463
    8,377
    0
    Location:
    Los Angeles, CA
    Vehicle:
    2008 Prius
    Model:
    II
    You have 2 really good hybrid shops around you. Luscious Garage and Art's Automotive. They have the expertise to fix anything on your car.
     
    Prius_Aki likes this.
  13. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,198
    6,461
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    Yes
     
  14. Prius_Aki

    Prius_Aki New Member

    Joined:
    Apr 21, 2014
    7
    0
    0
    Location:
    San Francisco Bay Area
    Vehicle:
    2009 Prius
    Model:
    N/A
    Thanks! Just noticed you had a similar issue in the past.
     
  15. Prius_Aki

    Prius_Aki New Member

    Joined:
    Apr 21, 2014
    7
    0
    0
    Location:
    San Francisco Bay Area
    Vehicle:
    2009 Prius
    Model:
    N/A
    So I got the car back from the dealer yesterday after declining the service. Couldn't get myself to pony up $2k quite yet. Good thing I didn't.

    Apparently, they did the troubleshooting checklist, but then it seems, basically guessed that it was the ECU (at least they couldn't really tell me how/why that determination was ultimately made). Afterwards, they apparently reset the DTC and whala, the braking issue went away (how is that possible?). They said that we must replace the ECU or the issue will happen again. I'm not refuting that it might happen again, but I still don't see how they are so sure it was the ECU.

    Anyway, I've been driving it around for a day and all is fine. Maybe it the braking issue will reoccur again at some point, but until then, it seems there is nothing I can do (save for replacing random parts in hopes that one of them is the source of the actual problem).

    Thanks again to everyone (especially Patrick) for your help.
     
  16. SageBrush

    SageBrush Senior Member

    Joined:
    Jun 4, 2008
    11,627
    2,530
    8
    Location:
    Southwest Colorado
    Vehicle:
    2012 Prius v wagon
    Model:
    Two
    Excellent!

    Consider replacing the 12V battery if it might be getting on in age. Random DTCs can result from a weak 12V
     
  17. Prius_Aki

    Prius_Aki New Member

    Joined:
    Apr 21, 2014
    7
    0
    0
    Location:
    San Francisco Bay Area
    Vehicle:
    2009 Prius
    Model:
    N/A
    Thanks SageBrush. Actually, I forgot to add the following:

    This whole braking trouble actually started at the same EXACT time the 12v battery went bad. We replaced it and since the braking issue didn't get fixed, we took it to the dealer.

    I asked them if the battery and the braking issue were related. They told me absolutely not, it was a coincidence. REALLY???
     
  18. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,198
    6,461
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    "Afterwards, they apparently reset the DTC and whala, the braking issue went away (how is that possible?)."
    The reason that this is possible is that the fault is intermittent. In post #7, I suggested that you clear the DTC if that had not already been done. The fault will eventually return, and when it does I suggest that you first replace the brake stroke sensor.

    I doubt that the fault is related to the 12V battery being weak.
     
  19. SageBrush

    SageBrush Senior Member

    Joined:
    Jun 4, 2008
    11,627
    2,530
    8
    Location:
    Southwest Colorado
    Vehicle:
    2012 Prius v wagon
    Model:
    Two
    I'll take your opinion over mine anytime.

    Question though: why would clearing the DTC change the brake performance back to normal ?
     
  20. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,198
    6,461
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    Because the fault is intermittent. So the brakes will work OK after the DTC is cleared, until the fault returns.

    While the DTC remains logged in the skid control ECU, the braking performance will be degraded because Toyota wants the owner to take remedial action regarding the fault, not just ignore it.

    Along the same lines, it could be that since the skid control ECU's performance is suspect given the DTC logged, the hybrid vehicle ECU assumes a degraded "limp home" performance profile which results in poor braking perceived by the OP.