Display is not giving accurate info

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.

 

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

 

+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