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

2005 Prius - ABS, VSC, Brake system, master warning light all on, no codes.

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Lazarus_, Jun 14, 2021.

  1. Lazarus_

    Lazarus_ New Member

    Jun 14, 2021
    2005 Prius
    Hi team,

    I've only had my 2005 prius for a couple of months now, 2nd owner, well maintained (log book) by previous owner. Car has been driving great up until a couple of days ago.
    I didn't drive it for 12 days and then on a short drive (<1km) yesterday the MWL came on, along with ABS, VSC, brake system (orange and red [handbrake off]). Car will not go into Drive or reverse now.

    I had RACV come and have a look, bloke plugged in two different scanners into the OBD, no codes were present.

    I unhooked the 12V, waited 5 minutes, hooked it back up and the car started fine, no lights. Drove <1km, same lights came back on. Again no D or R available.

    On-board screen diagnostic mode shows no codes.

    Recently topped up the coolant (engine and inverter) through the plastic reservoirs. Also topped up oil. This was about a month ago, have driven plenty since then with no issues.

    Images attached for dash lights. (SRS turns off after a minute).

    If anyone has any direction they could provide that would be great. I am okay to DIY. Moderate skills under the hood.

    Attached Files:


    TMR-JWAP Senior Member

    Aug 12, 2016
    Columbia, SC
    2007 Prius
    P0AA6 HV isolation fault most likely. It's the only RTOD HV fault that will allow you to continue driving the car normally after it triggers, UNTIL you turn it off. After that, it will not allow the car to go to ready mode. The only way around it is to reset the code, which is what you did by disconnecting the 12v battery. The code readers that were used apparently did not speak 'Toyota hybrid language", so didn't recognize the codes. Wouldn't be the first time....

    Frequently caused by electrolyte seepage from a HV battery module, but could also be cabling, inverter, transaxle or even the AC compressor circuit. If anyone you know has techstream, look under Hybrid Live for 'shortwave highest value'. This is a 0-5v measurement of the quality of the 'insulation/isolation' between the HV system and the chassis of the car. 5v is perfect, 0v would be a dead short. I think (iirc) a P0AA6 triggers around 3.2 volts. The vast majority of cars in good working condition are >4.9v

    The P0AA6 will also have a subcode available in it's freeze frame data. that subcode can help determine which section of the HV system the fault is located.

    But I may be wrong....wouldn't be the first time for that either....
    and after actually looking at the photos, that's a lot of warning lights. Maybe even more than I remember kicking on for a P0AA6. Will be interesting to see what codes you actually have. Will be important to get them read by a Prius capable scanner. That should be the first step, helps you to avoid all my BS guessing...
    #2 TMR-JWAP, Jun 14, 2021
    Last edited: Jun 15, 2021
  3. ChapmanF

    ChapmanF Senior Member

    Mar 30, 2008
    Indiana, USA
    2010 Prius
    It doesn't show any codes for anything but the infotainment gadgets. No use for the brakes or powertrain.

    If you don't have an OBD-II scanner, you can get the brake codes out (in abbreviated 2-digit versions) with a short piece of wire, by counting blinks of the dash lights.