Fried BCM ? fuse ? something ?
 

had a few drinks after work and attempted the sidemarker as signal mod today..

ill leave out most of the boring details besides the fact that i forgot to disconnect the battery before doing anything. and tapped into my signal wire and then connected it to my sidemarker, only did the driver side and went to test it when i realized everything was wrong. no sparks or anything during the process, but i must have shorted something out.
when key is turned to the on position the parking lights are all on (on the signal stalk it is in off position), on the dash it seems the car thinks my highbeams are on, yet i have no lowbeam or highbeam function at all, theres a solid beep that sounds, and the only way that any of this goes away is to disconnect the battery (figures as it probably wouldve prevented this at all. :mad0259: )
i did do a search prior to this thread, so im 90% sure that its the bcm or whatever its called, checked a variety of fuses, and changed the one for tail lights/sidemarkers but no change,

im sure this stupid mistake is going to cost me huge, but before it does, if there is anything else that anyone can think of that could be the problem, please share below..

Did you undo what you did? Are you sure the headlight control stalk isn't pushed forward in the high beam position? Did you check the "TAIL" fuse?

Undid what I did, the stalk is not in highbeam position, and yeah I replaced the tail fuse with a new one

Was the tail fuse that you replaced actually blown?

Are you just checking the fuse box under the hood or under the dash as well?

I'd double check your ground connection as well.


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The fuse was not blown, I replaced it anyways, then replaced all the ones listed in the manual that are related to the main body ecu even though none were blown, as for the ground connection the battery terminals were tight as shit, not sure where there are any other grounds to the chassis or anything, still no change through unfortunately..

Other than all the weirdness with the lights, and the beep tone, is anything else messed up? Does your car start? Does the A/C work?

Yeah the car starts perfectly, I tested everything else and it works; all climate controls, radio, Windows, door locks, interior lights, wipers
No limp mode or anything, can rev the car up perfectly, it's like it's just the lights control that's fucked.
Earliest appointment available at my dealer is next week Thursday so Im gonna see what they say is wrong.
I'm thinking bcm and I already found a replacement if it's not covered under warranty, and went over the replacement procedure in the tech service manual, so if thats what it is I'll just replace it myself (assuming of course that the dealer will charge large for it)

Please keep this post updated in case anyone has this issue in the future


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Will do, never know it might be useful to someone. And the only thread I found with exact same issues wasn't very detailed in the what was wrong department... I love details lol

Yeah, you may have fried the main body ECU, at least the portions that control the lights.

Would be interesting to know what happened. In looking at the circuit diagram http://www.ft86club.com/files/BRZwiringi.pdf, there really aren't many places that it directly interacts with the main body ECU. I assume you tapped the r-w from the turn signal (this is from the BRZ wiring diagram where the turn signal is in the headlamp assembly, but it should wire similarly) then clipped the red wire going into the side marker and attached the two together?

If you had a static charge at the side marker, the only place it could have hit the main body ECU would have been going through that TAIL fuse, which either wasn't enough to protect the surge and allowed it to fry the ECM at that TRLY point, or it's not the problem. Once clipped and connected to the wire you tapped, the sidemarker would not have been the problem.

So, assuming some sort of static discharge on the turn signal side, it would either hit the turn signal flasher assembly or the combination meter assembly. The turn signal flasher assembly has two fuses associated with it, 15A HAZ near the battery and 7.5A gauge in the interior fuse panel. You might check those two if you haven't already.

The combination meter assembly also has two fuses associated with it, the same 7.5A Gauge fuse mentioned earlier, and 7.5A MPX-B fuse located by the battery. I suggest you check that one too.


Another question, are the dash lights all on as well? The side markers are activated by the main body ECU at that junction that says TRLY (see page 176 of the circuit diagram) which activates the TAIL relay, which turns on the power to both the TAIL fuse and the PANEL fuse. The PANEL fuse activates the dash back lights, so if there is a problem with the ECU keeping that TRLY connector active, all that stuff would be on in addition to the side markers.

Since you say the headlights won't turn on at all, it makes me think it might be the ECU as well. They are ultimately also controlled by the main body ECU so, it is possible they got fried in there.

However, possibly you got lucky and somehow fried the headlight control stalk, which would be a cheaper fix.

Notttt exactly
I military spliced into the red wire from the turn signal as you suspected, but then military spliced right into the negative (black) wire on the side marker, rather than just clipping them together as I think I was supposed to. Not sure if that changes anything about what's happened..
Also I replaced the tail, panel, mpx-b, gauge, and hazard fuses, despite the fact that none of them were blown and no change :(
But yes the headlights won't turn on, and the dash lights remain illuminated with the parking lights (signal/marker/rear lights)
I'm going to bet 99% of everything I own on the unfortunate reality that it's the BCM, buuuut, since my appointment isn't till Thursday, would I be able to tell if the control stalk was fried by looking at it ? Or even looking at the BCM ? I had it out of the car and opened up earlier but didn't see anything that stood out as physically wrong with it..

Also despite the fact it may not fix anything, thanks for the time you put into that reply lol

I remember that thread (or very similar if not it) and people were more concerned with harassing the OP about screwing up the install than they were with trying to help.
There have been others on the subject (buried in threads with other titles) with issues that are exactly the same as yours and if memory serves me they all were related to the BCM being damaged.

or the junction block. I have the same issue, a new BIU did not correct the issue.. I have ordered just the junction block, fingers crossed this fixes it. otherwise its the gauge cluster.. :(

Well that's what I'm counting on I guess :/ I know I've come across some related issues in other threads as well, I'll just be sure to include lots of details in this thread with the pretty straightforward title lol

Just for the sake of giggles, did you disconnect the battery for ten minutes and then reconnect. With pure dumb luck sometimes things will reset.

they wont work.. it'll come on once the car switches on and will not turn off until you pull the battery..

Aha nah .. it was disconnected for an entire day or 2 and didn't change anything :p not that lucky, I'll update the thread Thursday when I find out what's up

junction block did nothing.. going to try the gauge cluster.

just be aware that you cannot just swap the dash cluster, as its part of a secutity set with the ecu and imobiliser modules. you either swap all three as a set ot you will need to get dealer to recode the new dash cluster to work with the ecu\imobiliser.

yeah, we're not trying to start the car , just verify that it fixes the issue of the light staying on.. if it does fix it I will be ordering another cluster to have my local tuner program the keys to it..

i dont think any tuners can do the security coding for security set modules, its generally dealer only and closly guarded, as it stops you stealing cars by swaping in an imobiliser and key set.

wasn't the gauge cluster either, so now we're looking at wiring issue somewhere.

I would try replaceing the dimmer switch relay. According to the wiring diagrams it ties into the high beams and interior lighting which is also tied into the exterior lights. It should be in the underhood fuse block labeled as "dim relay". I think the relay took a power hit and getting stuck in the closed position which is making the car think the lights are on.

Not dim relay

not biu/relay/gauge cluster/junction block.

stumped but they are back probing all the pins on the biu to verify what is back feeding to the biu to make it think the lights are on.

Hey guys, trip to the dealer cost me $750.. there was a broken ground somewhere in behind the bcm, the short never made it that far and I guess after they fixed the ground the hazard fuse blew, and I'm not sure if it was before or after the fix, but my headlights were both toast too, got so hot they melted lol
So it wasn't the BCM, just a broken ground and the short... Took them 5 hours in Labour to figure out, and then the cost of the headlights and a fuse and yeah... I'll never touch electrical again.

Wow, that was a tough one. Thanks for sharing your saga, may help someone in the future. Did they tell you exactly which ground point was broken?

I have some headlights I can sell you if you haven't bought them yet but from the sounds of it you got them already. Glad everything is up and running again !


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no unfortunately not, but they said it was somewhere near the flasher relay i put in when changing to LEDs
odds are I accidentally nicked it or broke it somehow when i put that in there or when messing around adjusting my clutch pedal :/

this same issue just happened to me. high beam light on dash and no head light or turn signals. everytime i disconnect the battery to reset and actuate the stalk for headlights, i trip something. any new news on this?

Sorry I failed to get as many details as i woild have liked when i picked my car up. More blown away by the near $800 bill just to fix 1 ground wire, and replace 2 headlights that blew up... I kinda forgot to ask what happened exactly

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Sorry to bump this thread from the dead but I ran across the same issue earlier today.

What's weird is I haven't changed anything electronically in my car for a while now so it I'm suspecting mine is also a wiring/ground issue. Will have it checked out by a technician later this week and report back on what's happening.

Electrical mods I have:
- HID (I have a 2015 FRS which comes with halogen standard)
- Switchback Turn Signals/Front Parking Lights
- LED front and rear Sidemarker bulb
- LED Turn signal bulb
- LED Map light
- LED Trunk Light
- Aftermarket relay for LED bulbs
- Dashcam hardwired in

I tried disconnecting them to no avail. I also tried disconnecting the headlight switch and issue persists when I put the key in accessory/on position

Update... it was the HAZ fuse in the engine bay lol

See this thread:
http://www.ft86club.com/forums/showthread.php?p=2941325

Exact same symptoms here, dash lights and high beam light on, beeping, headlights and tail lights wont come on.
This comment in particular got me home from work safely tonight, i spent two hours in the parking lot scratching my head until i found this. Unplugging everything, checked all the fuses under the dash, and wouldnt have checked under the hood fuse box had i not found this. Seriously, thank you.

Same problem :/
 

Sorry to constantly keep reviving this thread, but it seems this problem is pretty constant lol. Did you by chance find an alternative? I have the same exact symptoms, however my HAZ fuse continues to blow every time I replace it and I can not detect a short. Very frustrating 😅