I have a 2008 prius with 266K on it. I replaced the aux battery 4 years ago. Occasionally over the last year, when I press the power button.....all goes dark. This happened maybe once every 200 starts. Now it's about every 50 so it's getting worse. Through trial and error I've narrowed it down to the aux battery area. After all goes dark if I move the aux battery or gently move the positive terminal, it seems to connect and I'm on my way. The battery itself seems fine as all of the lights are bright when connected. The + / - connections are tight and free of dirt and corrosion. In my mind that leaves one of the smaller gauge wires connected to the aux battery. Does this sound familiar? Any idea of the cost? Thanks in advance for the help.
Wait, one of the "smaller gauge wires", plural? How many have you got? In my understanding of Gen 2, there's exactly one smaller gauge wire, plugged in at the positive battery clamp/fuse block, right next to the larger gauge power cable. The smaller one is only used by the DC/DC converter at the front of the car to measure the voltage at the battery. It won't be the culprit in the story you're telling here. If there are more smaller gauge wires than that attached to your battery, there may be some aftermarket mods involved, which could change the picture some. Some forms of contact oxidation are pretty much invisible, with the surfaces still looking clean and bright. If your symptoms change when you wiggle the stuff at the positive battery post, you're probably in the right neighborhood. There's the connection between the post and clamp, the bolted connection between the clamp and fuse block, the bolted connections at the legs of the large fuse, and the connection where the fat power cable plugs in, and the crimp where that connector attaches to that cable.
I'm still trying to decide if this is a real memory or not, but I might have heard of somebody who had a bad battery, with a flaky connection inside the battery at one of the posts, depending on how you wiggled the post. A multimeter or a test light is a handy way of seeing how far the 12 V does and doesn't get, while you're wiggling the suspected things.
What does go dark mean You push the brake and hit the button the car readys and you have no display or the car readys and you can't see the word ready or anything on the display but the headlights are nice and bright as are the turn signals in the running lights?
So I took a couple of pictures-see link. By "going dark", I meant there is absolutely nothing on, no dash lights, no ready light, no dome lights....like there is no connection to a battery. When I move the aux battery and it re-establishes a connection, all of these lights on and relatively bright. Note that the dome light is on before I push the start button. Once I press it all goes dark. hope that makes sense. Tom
So yes your experiencing the CM monitor display problem and when you go back there and play with the battery if you don't mess with the positive just deal with the negative post where it attaches to the frame of the car right behind that little piece of plastic under the rear bulb changing plastic access panel you will see the 10 mm that connects the ground to the body frame clean that up if you like and then make sure all that's tight. When you open your door if you do not see the door open insignia lit up in red on the dash you are not going to have a display so close your door go open your trunk and when you open your trunk you still on the front display of your dash do not see the door open indicator move the ground wire that you just cleaned and attached and when you see the door open sign on the dash which you're looking at while you're doing this the minute you see that door open red icon light up you will now have a display tighten the bolt close the trunk open the door see the red door open light push the start with the brake down and you have a full display. You open the door and don't see that red door open sign No display is going to be on your dash guaranteed.
What you are experiencing is typical of one or more of the battery connections (or where the ground strap connects to the car) being loose.
An update on my issue. The negative terminal and ground were tightly attached, but I cleaned them and tightened again just in case. I believe the issue is (see 1st picture above) that the bracket that goes across the battery and anchors the positive apparatus down had 1 side where the nut had come off. I've got a new one and fastened it down and so far so good. If that is not it I'll report back, but it's worked for 2 days now. Thanks again for the help. Tom
