Is it the BCM or something else?

Good evening everyone. First I'll say hello, I'm Nessa. And I apologize for the long post. I'm actually here for some help with my son's Tundra. It's a 2012 5.7L 4Wd crewcab. He has an aftermarket radio and 15" subs installed and the subs and amp run off a separate battery which is wired to the alternator. He is not using the stock alternator, he upgraded to a larger one about 6 months ago to handle the subs and amp. He was driving to his friends house Tuesday when the back battery began to arc. He pulled over and unhooked the battery. When he got to his friends, the truck began to go haywire. He lost all the gauges including fuel, speedo, oil, temp etc. He also lost radio, power locks and windows, running lights and brake lights. He still has turn signals and headlights. And the windows will roll up if you hook a battery to the window motor. When he got to his second stop and shut the truck off, it would not recrank. After jumping it, it fired up and loaded on a trailer for the trip home. Jumped it again and drove it off the trailer then it died. Pushed it into his spot, let it sit for a few mins then it fired up 3 times in a row but still no interior electronics. Fourth time of trying to start it, it tried to crank but just did the "dead battery" or bad connection noise. Checked fuses and husband says they all appear good. They're thinking BCM (which is apparently a difficult part to find without going to Toyota) but is it possible for there to be another issue we're missing before we replace the BCM?

 

Ouch! You might want to describe how it was all hooked up. It could be fuses or relays that dies if all of the circuits were properly protected or isolated, but it's hard to tell without a schematic of how it was all connected.

And Welcome from LA (Lower Alabama)!

 

Good morning Bakershack. Thanks for the welcome. So the head unit of the radio was installed at a shop as well as I believe all the wiring for the subs and the amps. Backseat has been taken out of the truck and the subs are in a box on a platform that is stable and secured to the body of the truck. Amps are bolted to the side of the speaker box and the battery in the back is in a box by itself and is screwed to the platform that the subs sit on. All wiring is run through the body of the truck through the firewall and I believe the main power wire for the back battery and the subs and amps is run directly to the alternator. He's had the same setup for close to a year now and has not had any issues until Tuesday night. Only thing that's been replaced on the truck is the rack and pinion and he had to put a new rear end in when his rear end blew and that was about 4 months ago other than upgrading the alternator to be able to power both batteries and his amps and subs.

 

You would really need to hook up a decent scan tool to the truck to see if there is communication with the BCM to know whether that is the culprit.

How is the other battery? The failed battery may have also killed the good battery, and this is absolutely the first thing I would check.

 

They tried hooking it to a scanner Tuesday night but there was no communication between the truck and computer. I'm not sure if that may have been due to the truck battery being dead and not starting or not. Currently charging the main battery now to see if it will hold a charge or if it's shot. Also checking fuses under the hood and behind the kick plate in the cab with a tester light.

 

There should also be a fuse between the stereo battery and whatever feeds the stereo battery, and any failure of that second battery should have opened that fuse immediately and left the rest of the truck alone.

 

Ok, we will look for that fuse while we wait for the main battery to charge. Thanks for the info. I know at one point he had a fusable link on his main power wire.

 

Okay checked all the fuses under the hood and they all show okay, but nothing from any of the fuses in the cab. Put the battery on the charger for about 2 hours and the truck fired right up and is running. Gauges came back but the dash is lit up with everything, brakes, traction control, wiper fluid,etc. Also still no brake lights,no running lights no power windows no power locks, radio, etc.

 

Have the battery load tested.

 

Check the alternator. There have been reports of higher amp aftermarket ones not working right. What voltage is it putting out?

He should also look in to the big 3/4 wire upgrade. Search this site for it.

 

This was my main concern. The arcing of the sub battery sent a current surge back into the rest of your electrical system. Proper fusing would have prevented that. It looks like you're making progress since I was online last night. I hope you can communicate with the BCM. That would be an expensive replacement.

 

Just ordered a new main fusable link from Toyota. Can't really tell if his is blown so figured we'd start with the $40 part first since I've read posts in here suggesting it may be blown. It'll be here Monday so we'll see what happens when we change it out. Also gonna have them try to hook it to the scanner again since the battery is charged and see if it'll communicate. Just kinda lost since it'll fire up and run, but we can't get any type of fuses under the dash to show any type of light on the test light.

 

Just out of curiosity I have one doing the same how did you fix the problem. Thanks any help will be appreciated

 

Your son might have melted the fuse block where all the relays and fuses plug in. His sporadic voltage issues

I guess he forgot reading the instructions that came with the subs and amps about in line fuses.

Most of us car guys are here because we were stupid once.

 

LOL...I did resurrect a dead thread, sorry

 

Technically the prior poster did. He got you though!

 

i will go to bed, working the night shift, wearing my head of shame, lol

 

I’m hoping that they found the reason behind this problem because I’m having the same problem with stuff not working exact same problem. But mine came from a different issue. Any help would be grateful.

 

Giving a helpful bump to a guy who I hope doesn't have a locked up Transmission