I recently bought a 2005 Prius with 164,000 miles knowing the red triangle warning light, check engine light and VSC lights were on and that it wasn’t running quite right. All signs that the battery needs to be replaced, which I plan to do with one from newpriusbatteries, but I’m wondering if the ecu may be bad or anything else as well. I hooked it up to a Mini VCI to see what the codes were and got P0A1F, P3000-123, C1259, C1310, U0123, U0124, U0126. I’ve been reading up on all the threads but am stumped on where I should start. The attached pictures show my freeze frame from techstream, the battery voltages are all over the place, including many negative (-25.07V up to 24.98V). I can’t find anywhere that talks about this kind of situation. If I try to clear the codes they come back immediately. Any help on where to begin diagnosing would be greatly appreciated!
The weird voltage readings indicate a problem with the battery voltage sensing wires. Having multiple odd readings suggests the orange plug at the battery computer is corroded. The battery fires at ECU sense connector thread | PriusChat The U0123, U0124, U0126 codes are all communication problems with the skid control computer.
This. When live data reports negative numbers or 0 for block voltages the sensing harness and ECU are done for. STOP driving the car right now, it is currently a fire hazard. Immediately disconnect the battery ECU and remove the sensing harness. I had one of these batteries catch fire right in front of my eyes and it wouldn't go out until I partially disassembled it. Your battery modules might still be good and the battery computer can be repaired since it's able to communicate. If you wait a few days or a week the modules which are currently shorting will fully discharge and will need to be replaced.
Thanks for the replies! You both were right on, I finally got the battery pack out to have a look and this is what I found! Not overly surprised since I think the previous owners drove it quite a bit after the red triangle. I tested all the modules with a multimeter unloaded and all but one read ~8.3V. One was 6.5V. I have the new battery with cables on order and a used hv ecu on the way. Hopefully this combination will bring everything back into order and the car will run like it's supposed to. I'll let you know how it goes. Any other suggestions anyone has are always welcome!
This is the hv ecu I just received from ebay. Based on the thread Brad pointed me to I'm wondering if I should be concerned about the corrosion starting on pin 22? Should I return it? Clean it? How? Thanks again!
The safest thing to do is to not use that ECU. I would not use it in one of my rebuilds. However, it would take years or never for it to short like your original ECU. The cause of this corrosion has not been determined. Just a small percentage of the ECU's are effected. Climate is a factor. They do not corrode in the dry heat of Phoenix. A cleaned ECU might just start corroding again. Or it could stay clean as long as any other. It would take years to test.
Thanks Brad, I bit the bullet and ordered a brand new ecu. I figured if I'm paying for a brand new battery I don't want to take the chance and have a used ecu ruin it. Hopefully the investment pays off
Thanks for this topic and the various posts. As always, Priuschat is the go-to for weird Prius questions. I just wanted to comment that my 2004 Prius with SKS that I rebuilt the HV battery on 3 years ago, starting throwing the P0A1F code and said "problem" on the multifunction display. This happened immediately after I'd turned the car on to READY and then opened the driver door and then moved the car, which causes the red triangle. I turned off the car and when I went to start it this powertrain error had been logged. I know this because I used Torque pro to scan the codes. Sorry I don't know with of the 3 detail codes that goes with this error I had. Anyway, since my 12v battery is from 2012(!) I first suspected that, but it was reading 12.3 at the terminals. Not great, but no awful. I decided I might have to replace that battery finally, as I suspect a couple MPG loss due to it. Anyway, on a whim, I just used Torque Pro's reset codes command and...it seems to be fine. I think a disconnecting of the negative 12v battery lead might do this also. So, if you recently drove with your driver door open, or had a weird usage-related error, try resetting codes. By the way, I've had the RToD from leaving the OBD2 scanner connected also for several days I believe. Yeah, it could be a weak 12v... EDIT: I went back to check the state of charge differences and the voltages of all the 14 pairs of modules with Torque. The HV battery and its modules seemed fine. A recent Dr Prius test after 3 years had it at 85%. I know this error is an ECU error, but I wanted to be sure I didn't have HV battery obvious issues...
