Hello Everyone,

Bought my son a 2012 xB and he couldn't be happier, well until yesterday.......

Have had zero issue with the car in the past month but yesterday he drove it to his first day of school and decided to get a coffee before school. Parks the car, gets coffee comes back to a car that has ZERO power. No cabin light, no dash lights, not starting, nothing.

I came to pick him up and take him to school and then tried to figure out what was going on. There were no warnings, no battery light or anything like that. I tried to jump-start it and NOTHING, no lights no charging of the battery at all. Checked all the fuses and nothing looked bad. So I took out the battery and had it checked at an AutoZone nearby and they said it had a 89% charge but was showing as a bad battery. The good news was it was an AutoZone batter and was under warranty and they gave me a new one, so I figured there was no way it was the battery but we got a new one out of this whole thing anyway ;). I get back to the car and hook up the battery and as I thought, nothing working still. So I went back to the fuses and double-checked it all and then decided to give a good smack to the relays out of frustration and to see if maybe something was stuck there and BAM the light in the car turns on (we had turned on the dome light so I could see if the power came back on). The car started straight up and everything was fine!

So I'm guessing a bad relay? But is there a main relay for the whole electrical system? Which one of them might it be? Or did I unknowingly hit something else? Again, these were the relays in the fuse box under the hood.

Any input is GREATLY appreciated as this one has me confused.

___

 

Don't "check" fuses, pull them out and measure with multimeter and verify resistance readings. If I had a nickel every time I've heard "fuse looks OK", but didn't actually conduct any electricity... I actually fired mechanic from my shop over that.

Might some corrosion in fuse-box. When pulling fuses, examine metal terminals where they plug in. Is it white and powdery? Or shiny silver metal?

Also wiring under fuse-box can corrode. Unbolt from car and flip over.

Battery cables and grounds can be corroded. These are only things that can be single point of failure that can cut off all power. Previous owners may have hacked up wiring going into fuse-box. Examine each and every wire closely and carefully. Same with each connector at each end of each cable.

 

Appreciate the info. We don't live in a humid area so there is zero rust issues or corrosion usually, every fuse is clean as can be. A fuse though wouldn't knock out all the power to the car though would it? Fuses would be for lower voltage items and would take out only one system, so if I had dash lights, headlights etc and no starting then it would be an ACC type fuse. Now thinking about it more, I'm guessing it's probably something to do with the battery cables or the main harness going to the fuse box.

There is no splicing in the harness, I followed the harness from the positive cable to where the harness plugs into the fuse box and the ECU and there was no splicing or bad connections. It's running fine now but I just don't want it to cut out all power while he's driving on the FWY to school or something like that. Might just change out the battery cables as a preventative measure. Is the positive battery cable wrapped up in the harness? I can see the negative is simple but the positive seems to be tied up with other wiring.

 

There are three main points of failure that can cause a complete 'dead' electrical system failure.

Main battery power cable
Main battery ground cable
and
the main fusible link in the exterior fuse box

For the battery cables you will need to check both ends to make sure they are corrosion free and tight at both ends. This is easy for the power cable as you've seen since you checked it. The ground is easy at the battery end, the other end bolts to the car underneath the air box. You'll have to pull the air box to get access to check it.

For the fusible links you need to test them with a multimeter to make sure power is going into them and coming out the other half. Unfortunately this only works when the problem is present so you'll need to visually inspect them to see if one is partially blown or not.

Here's a video of them in a Corolla. Same location and almost same fuse box so it's useful.