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Display is not giving accurate info

Discussion in 'Generation 1 Prius Discussion' started by Paul Baillie, Jan 19, 2014.

  1. Paul Baillie

    Paul Baillie Junior Member

    Joined:
    Sep 13, 2013
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    Location:
    Hilo, Hawaii
    Vehicle:
    2003 Prius
    Model:
    I
    I bought this 2003 Gen 1 in july 2013 with 58.6K on the clock. Shortly after buying it the red check engine triangle on the dash came on along with the red rectangle (with car outline inside and "check main battery" in the hybrid display. Finding a local shop with some Hybrid experience was a lucky break (i've found the dealer to be a complete waste of time!) They checked my main battery, found two leaking cells, corroded buss bars and battery cables, after replacing these items the display returned to normal function for awhile before starting to give the triangle and rectangle warnings intermittently, at which point I had the shop check the codes again several times. The problem as near as they can determine is still corrosion/connection related and recommended replacing the rest of the main power cables. The car now has around 63K on it and has run flawlessly, getting between 46 and 50 MPG, but the display does not give accurate info. In the consumption mode it reads 99.9 MPG all the time and the bars on the graph are always pegged to the top, if I switch to the Battery mode it does not show energy moving in either direction, some times the triangle will come on with the Hybrid display still reading (not accurately) other times both warning symbols will come on with no multifunction display info and then things will return to normal (no warning symbols but also no accurate info) When the battery work was done they checked the battery computer module and said it looked surprisingly good, no corrosion. At this point my plan is to replace the 2 main under car cables (battery to inverter) and the 2 inverter to trans axle cables, does anyone out there have any insights or suggestions? and where is a good place to find these heavy power cables? after market if possible.
    Thanks for any help, Paul Baillie
     
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
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    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    Hi Paul,

    1) What is the current DTC posted? If it is P3009, that confirms there is a high voltage ground fault.
    2) Assuming you have logged P3009, I suggest a more systematic approach to finding the source of the ground fault. This requires you to purchase a megger, which is basically like an ohmmeter but uses a very high voltage to determine resistances for which a regular ohmmeter would display infinity.
    3) If you cannot afford to buy the megger (which will cost a few hundred dollars) then you can try using a regular ohmmeter. Perhaps the ground fault is severe enough that an ohmmeter will reveal the problem.
    4) Once you have a suitable device to measure resistance, the concept is to measure resistance from a high voltage line to ground. You should measure infinity. If you measure some value less than that, you will know you have a high voltage ground fault there.
    5) Then you can decide what the problem is. The ground fault can be at any component exposed to high voltage, such as the traction battery, the traction battery ECU, the cables between the traction battery and inverter, the inverter, the cables between the inverter and transaxle, and finally the two MGs within the transaxle itself. Disconnect the cabling to isolate components before doing measurements.
    6) Once you have determined the faulty component, then you can decide whether it is worth while replacing it or not. You are not going to find aftermarket parts for a Classic Prius. You might find used parts from a salvage yard. If you want to buy new parts, I would buy from one of the Toyota dealers that sell at a discount over the web, such as:
    AutoNation Toyota Gulf Freeway Parts | Toyota Parts Online - Genuine OEM Toyota Parts and Accessories - Houston, Texas
    7) Finally, as you pointed out, the power train is performing flawlessly, so you have to decide how much cost you want to incur to resolve the problem. The ground fault is potentially a safety issue in the event of an accident that exposes you or the vehicle body to high voltage.
    8) If you are going to DIY, you need to be aware of all of the safety issues and precautions associated with working on the high voltage hybrid system. Subscribe to techinfo.toyota.com to obtain Toyota factory repair manual and electrical wiring diagram info. This will also provide you more insight regarding how to address P3009 or any other DTC that your car has logged.
     
  3. ChapmanF

    ChapmanF Senior Member

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    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Hi Paul,

    I'm struggling to imagine how the shop got from the symptoms you're having to suspecting the main power cables. Have they really looked at the ends and found the terminals corroded, too badly to clean up? Something seems off the wall to me.

    If you're looking for the cable, it's this kind of stuff (ignoring the "Unshielded" section because the car uses shielded), but I'm not sure where you'd buy any in sub-spool quantities, and by the time you figured out where to get the proper terminals and the proper crimp tools for both center and shield, you'd have bought the assembly from Toyota many times over. (Anyway, I can't imagine you'd go wrong just pulling the part off a wreck as long as the damage was elsewhere - it's not a part I hear of going bad.)

    But before we can make any better guesses about what's going on, we need data, and it sounds like your MFD isn't giving you that. If you can get your hands on a Prius-aware scanner we'll be getting somewhere. A ScanGaugeII is handy because you can drive around with it on your dash like an extra instrument and have it show you battery current and status and other interesting parameters you're not getting from the MFD now. The Torque smartphone app is also one people have used in that way.

    One important thing to see first is whether the scangauge (or other scanner), showing you the battery state-of-charge and current straight from the Battery ECU, shows you the same bogus values you're seeing on the MFD, or shows you good data while what the MFD shows is still bogus. If they're both bogus, I'd tend to suspect the Battery ECU or other wiring back at the battery. If the bogosity is limited to the MFD, I would run its own diagnostics and make sure it's communicating correctly with the other nodes (probably the Gateway ECU in particular) that it needs to chat with.

    If I remember right there are a couple of pieces of Battery ECU data that are mirrored in the HV ECU as well (looking at the PID database, you can read battery SoC and current as PIDs C9 and D2 in the HV ECU as well as PIDs 91 and A3 from the Battery ECU). It might be a clue of some kind if they don't closely match.

    Good luck,
    -Chap
     
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  4. ChapmanF

    ChapmanF Senior Member

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    Location:
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    Vehicle:
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    IV
    +1. In my post somehow 'ground fault' wasn't occurring to me, but it sounds plausible enough. As usual, having a Prius-aware scanner and getting the codes will really help track down the issue.

    -Chap