Like so many others, I have been appreciating your help from the shadows, but today I step into the light with an issue I haven't seen anywhere else, seeking an answer to 2 dumb questions. 2008 Prius hatchback, 2nd owner (2015), 176.6k miles. Forgive the length, but I didn’t want to leave anything out that may be relevant. I bought a new 12V earlier this year and after its install, the car would randomly die. I’d go to start it and nothing, when it finally started the clocks, windows, stereo had been reset. Sometimes the lights would be on when I opened the doors, and would go out as soon as I stepped on the brake. This went on, intermittently for months, and I took the battery to be tested several times during that period. I also had no issues jump starting it, but I know that’s not great for this car, and it was jumped approx. 10 times during this period. Long story short, after a myriad of trouble shooting it was discovered that the battery post needed to be adjusted because it was too short and the terminal had a good connection at the bottom but not the top. Over the summer I had decided to do some general maintenance that included the engine water pump, and when I drained the coolant it was the red stuff and not SLLC, making it obvious that there was work done to the car that didn’t appear on the service record or the Carfax. I was unable to complete the repair due to an unrelated injury and called someone else in. Everything seemed fine until 50 miles later, I discovered that the coolant tank hadn’t been plugged back in. I wasn’t happy about it, but he wasn’t a hybrid mechanic and he’s the one who solved my 12V issue. Shortly after that, I decided to purchase the Hybrid Automotive Reconditioning System, but only had time to do a charge. Afterward, I checked the performance of the blocks while driving with torque pro, and the VSC, ABS, and Brake System Warning light came on. They didn’t come back on the next time I started the car, but I ran techstream when I got home and pulled DTC’s u0123, u0124, and u0126. Communication issues with the skid control ecu. I learned that driving while running the app can cause that, but given the above-mentioned issues, I decided to being troubleshooting. The first thing the repair manual has you do is check the 12V, and the reading at the jump point was very low, and bouncing all over the place, but when measuring at the back it was around 12.6. I checked the voltage several times and yielded the same results. Low voltage in the front, high in the back, and not cool at all (it’s a mullet). I’ve seen the jump point settle at 0.48V and around 2V, 8V, and 11V, each time jumping all over the place before stabilizing. Each time a good voltage read at the battery. It should also be noted that after opening the hatch and going back round to check the jump point, immediately after checking the battery, yielded a result in the normal range, around 12.4V. I couldn’t find anything online about that happening to anyone else, and I don’t know if any or all of the above would cause something like this. In the meantime, I decided to look for a short in the CANbus starting at the OB2 port, then moving to the skid control ecu. After removing the dash to reach it, I realized that I had missed an important step, unplugging J15/C1 and J18/C2 before checking the resistance. So, any measurements I have are incorrect. Problem is, despite having the wiring diagrams, I can’t locate the junctions. I have a general location, but I’m not sure which thing to unplug. Can someone show me or describe to me which connectors I need to be working with? Also, if there are any ideas as to what would cause the difference in voltage from the jump point to the battery, I’d appreciate hearing them.
Only two reasons for that: You are not doing the measurement right. OR There is a bad connection on one of the main battery cables. The most common place for that to happen is where the negative cable connects to the body (ground). I don't include a blown main fuse because I don't know if there IS one between those points but that could be a reason too. You NEED to get that figured out and fixed BEFORE you do anything else.
The 12V is definitely being measured right, as I've done this many times over. I know there is a bad connection somewhere, but if it's a main battery cable (and I'm not saying that it isn't), then I am looking in the wrong place. How would I go about determining that?
I didn't word that right. I know how to check for a bad connection, how to I check to see if there's a short?
When you check aux voltage at the battery, are you checking from positive terminal to negative terminal? If so, check it from the positive terminal to the car's frame. It sounds like a simple loose ground connection either at the negative terminal or where that wire connects to the body. Edit to add: What the heck is a mullet? I thought that was a fish or a hairstyle.
Did you have one back in the day? Or were you all business with no party in the back. If so, you mind sharing a pic. Always fun to look back at the past .
In this case, it's a metaphor. It's got low voltage in front and higher voltage in back. I was checking at the posts, I have it all torn apart right now, so I guess I'll have to wait until I get it back together before I can test terminal to body.
LOL! You asked for it. This was 1974. Probably as shaggy as this dog ever got. I don't think mullets were invented yet, and by the time they were, I was smart enough to not get one. By the way, that amazing woman still tolerates me after all these years. Hooda thunk it? That's really good! I should have caught that. One thing you can check even before putting the 12V back in (if the negative cable is still in place) is to jiggle the ground wire where it connects to the body or even check the resistance there.
This can't be caused by a "short" because there would be smoke and fire along with it.......unless there is a blown main fuse due to a short.
I checked the connection in the back, and it seemed well enough. I removed it and adjusted it anyhow, and it's right as rain. Thank you for your help there. I am still curious about the location of j15/c1 and j18/c2??
