2006 Prius MPG dropoff - battery pack?

Discussion in 'Gen II Prius Technical Discussion' started by DPSWL, Sep 13, 2012.

  1. DPSWL

    DPSWL Junior Member

    Sep 13, 2012
    Your Vehicle Year:
    2006 Prius
    I am a newbie to this site, but love my prius.

    I have noticed a significant (15 to 20%) drop-off in mpg in the last 6 months or so. My 2006 prius at 95,000 miles is just short of the warranty on the battery pack. I brought it in to the dealership and they ran the routine computer diagnostics and said everything looks good. I fully expected them to tell me that the performance on the batterpack had fallen off, so I was a bit put out. The guy actually got a bit defensive with me when I asked him some further questions about what the criteria are for determining whether the battery back was performing as it is supposed to in order to get the maximum MPGs.

    Is it possible that the diagnostic machine would indicate that everything is fine, but the battery pack NOT be fully up to par?

    Sadly, I'm not sure I trust my dealer with acknowledging a functioning, but poor performing battery pack just short of the warranty period being up.

    Any comments or suggestions are greatly appreciated.
  2. richard schumacher

    richard schumacher shortbus driver

    Mar 27, 2004
    United States
    Your Vehicle Year:
    2004 Prius
    As a long-time owner I assume you know about low rolling resistance tires, tire inflation, the effects of short trips, not overfilling the oil, and the like. If you still have the original 12V battery you should check it yourself, either with a voltmeter or the built-in test procedure:
    Weird stuff happening? MPGs dropping? Test The Battery | PriusChat
  3. edthefox5

    edthefox5 Senior Member

    Jul 25, 2007
    Clearwater, Florida
    Your Vehicle Year:
    2007 Prius
    Replace Inverter Coolant and install Mobil 1 synthetic oil. Replace trans fluid.
  4. uart

    uart Senior Member

    Sep 7, 2009
    Your Vehicle Year:
    2005 Prius
    Hi DPSWL. They generally wont do anything unless it throws an error code. Apparently the battery can lose a very large percent of its capacity without throwing a code, provided that the other parameters like voltage and resistance are ok.

    That being said however, tests have shown the Prius can still get very good fuel economy even with a large loss of battery capacity, and there are many other sources of possible MPG loss to consider.

    Have you noticed ant anomalous behavior of your traction battery SOC during regular driving?