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2006 Prius HV Battery full, limp mode, DIY help

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by titan_prius, Feb 9, 2023.

  1. titan_prius

    titan_prius New Member

    Feb 9, 2023
    2006 Prius
    I recently took out the battery of my 2006 Prius (170k miles). Before, my battery was draining very quickly. When idling the battery would almost rapidly drop to purple and the ICE would come on, which seems to be a common issue with battery age. It would charge back up just fine. I have a mini VCI and TechStream and found I had intermittent P0A80 (screenshot 1). Eventually the car went into limp mode a few times, and I decided to band aid fix until I could afford a new battery.

    I replaced some weak modules(after sitting outside the car for about a week. All measured between 7.6-7.4, except for 4 outliers below 7.3), and after driving the car for about a week it seemed my problem had been solved. The battery could hold a charge much longer and my mpg improved. Idling did not cause the battery to immediately drain. It drove fine for about a week.

    Then I got some warning lights, techstream read P3017 (battery block 7 becomes weak), P3021 (battery block 11 becomes weak) and the battery fan in the back of the car would blow max speed constantly. I cleared the code a few times (fan turned off) and drove for a few days in between. It became more frequent and eventually engine would rev up and the car would go into limp mode again.

    I opened up the battery again and this time I replaced modules in block 7 and 11, and charged each module to 8.3 volts before putting it back in. Now, almost immediately, warning lights appear and I get P3019 (battery block 9 becomes weak), and max speed battery fan. And almost immediately afterwards the car goes into limp mode. In TechStream's freezeframe (screenshot 2), even though it lists block 9 as weak, block 9 is the highest value in the screenshot. Also, the battery temperatures in the screenshot don't seem high enough for the fans to blow max speed. It is the middle of winter here in Virginia.

    I know the MFD is not a proper source for a diagnosis, but it shows some interesting behavior. The battery holds an almost full charge, but is only used (yellow arrow to the wheels) when moving very slowly. When accelerating or driving above 10 mph, the engine takes control and also charges the battery. The battery powers the wheels for only a split second before the battery starts being charged by the engine. I can't find any other examples with this behavior, as most people experiencing this issue have almost empty batteries when the car relies on the engine. However, mine is almost full and is not participating. Even in TechStream it shows that the battery state of charge is 50%+.

    I think I made a mistake when putting the battery back in. I haven't put the trunk or walls back in, because I expected I might need to remove them again soon. I followed these two videos:

    If anyone has experienced something similar I would appreciate the help. Also if anyone knows what in screenshot 2, "Batt Pack Current Val" means, and why it is negative. In all the TechStream screenshots I have seen it is always positive. Sorry for the essay but I can provide more info if needed. Thanks.

    Attached Files:


    TMR-JWAP Senior Member

    Aug 12, 2016
    Columbia, SC
    2007 Prius
    That parameter is a measurement of the electrical current (amps) discharging from the HV battery (positive value) or entering the HV battery (charging, negative value).

    So, in your first photo, the HV battery is at a 7.98 amp discharge. Your TS screenshot is showing you have a problem with blocks 11 and 12.

    In the second photo, the HV battery is undergoing a 17.24 amp charge and your TS screenshot is showing a problem with block 9.

    One of the first things I would do, since you've already disassembled the battery, would be to verify all my fastener torques. All those 8mm hex head nuts need to be torqued to 48 inch-lb. (INCH-LBS not ft-lbs). Too many DIYers cause their own heartache by not properly torquing these fasteners.

    Make sure you're counting modules correctly. Block 1 module 1 on a Gen 2 is the module furthest from the ECU. Module #1 on a Toyota is always the module that has the heavy orange cable connected to the (-) terminal.
    #2 TMR-JWAP, Feb 10, 2023
    Last edited: Feb 10, 2023