BCM and lighting?
Thread Starter
Staging Lane
Joined: Mar 2020
Posts: 65
Likes: 4
BCM and lighting? Can anyone confirm the duty of lighting control through the body control module?
I've recently noticed my signal lights go wonky along with the common window and radio BCM symptoms.
Whacking the console on the right side usually gets it all back but I plan on reflowing the board and
I'd just like to know if it's a coincidence or related before I get in there.
2000 Firebird Formula
I've recently noticed my signal lights go wonky along with the common window and radio BCM symptoms.
Whacking the console on the right side usually gets it all back but I plan on reflowing the board and
I'd just like to know if it's a coincidence or related before I get in there.
2000 Firebird Formula
Last edited by Bruthajoe; Oct 25, 2025 at 08:42 AM. Reason: Add vehicle
Joined: Nov 2003
Posts: 11,328
Likes: 345
From: Jacksonville, FL (originally from Toronto Canada)
The BCM is not involved in the turn signals in any way. It manages the interior courtesy lights and the flashing of the external parking lights as part of the keyless entry and optional alarm systems, but not the signals.
Thread Starter
Staging Lane
Joined: Mar 2020
Posts: 65
Likes: 4
I'm all ears if anyone has a guess. To recap The problem is intermittent loss of and erratic voltage to the (amber) signal/running lights. Smacking the console like Fonzie from Happy Days can fix it.
Joined: Nov 2003
Posts: 11,328
Likes: 345
From: Jacksonville, FL (originally from Toronto Canada)
Well yes, I suppose it is possible for the BCM to affect the running/parking light circuit since it controls flashing them for the alarm/keyless entry. What I said was that there is no way for the BCM to affect the turn signal circuit. There are two filaments in each of the lamps involved and each filament is on a different circuit. The dim filament is used for the running lights (when the headlights are on) and the parking lights (when the headlight switch is in the P position) and those are the lights which are flashed via a relay by the BCM for locking/unlocking the doors by remote and for arming/disarming and activation of the optional alarm system. The bright filaments in front are used for turn signals and daytime running lights (DRLs). In back they are used for turn signals and brake lights in Firebirds or just brakes in later model Camaros with separate amber rear signals.
Please describe in more detail the symptoms you have. Do the lights fail only when the the turn signals are on? Do they also fail when the hazard flashers are on? Do they flash unexpectedly when the signals are off? Or flash the wrong side? Is it only one side or are both sides affected? Do the rear lights flash or fail in the same way? Knowing these details will help determine which circuit is involved to help diagnose the issue.
Please describe in more detail the symptoms you have. Do the lights fail only when the the turn signals are on? Do they also fail when the hazard flashers are on? Do they flash unexpectedly when the signals are off? Or flash the wrong side? Is it only one side or are both sides affected? Do the rear lights flash or fail in the same way? Knowing these details will help determine which circuit is involved to help diagnose the issue.
Thread Starter
Staging Lane
Joined: Mar 2020
Posts: 65
Likes: 4
Well yes, I suppose it is possible for the BCM to affect the running/parking light circuit since it controls flashing them for the alarm/keyless entry. What I said was that there is no way for the BCM to affect the turn signal circuit. There are two filaments in each of the lamps involved and each filament is on a different circuit. The dim filament is used for the running lights (when the headlights are on) and the parking lights (when the headlight switch is in the P position) and those are the lights which are flashed via a relay by the BCM for locking/unlocking the doors by remote and for arming/disarming and activation of the optional alarm system. The bright filaments in front are used for turn signals and daytime running lights (DRLs). In back they are used for turn signals and brake lights in Firebirds or just brakes in later model Camaros with separate amber rear signals.
Please describe in more detail the symptoms you have. Do the lights fail only when the the turn signals are on? Do they also fail when the hazard flashers are on? Do they flash unexpectedly when the signals are off? Or flash the wrong side? Is it only one side or are both sides affected? Do the rear lights flash or fail in the same way? Knowing these details will help determine which circuit is involved to help diagnose the issue.
Please describe in more detail the symptoms you have. Do the lights fail only when the the turn signals are on? Do they also fail when the hazard flashers are on? Do they flash unexpectedly when the signals are off? Or flash the wrong side? Is it only one side or are both sides affected? Do the rear lights flash or fail in the same way? Knowing these details will help determine which circuit is involved to help diagnose the issue.
Joined: Nov 2003
Posts: 11,328
Likes: 345
From: Jacksonville, FL (originally from Toronto Canada)
That sounds more like a problem with the DRL module which is mounted to the defroster duct directly behind the radio. It controls the switching of the front lamps between DRL mode and turn signal. There are internal relays which manage that switching. It's possible that the relay for the right side is sticking and failing to engage properly. Unfortunately, the internals of that module are considered "non-serviceable" by GM although the relays can be replaced if you're good with soldering on printed circuit boards.
There are ways to test the DRL module but they are somewhat complex (using a multi-meter - there is no specific tester available) and not always reliable when investigating an intermittent problem. If you really wanted to confirm, you could remove the radio and then tap the DRL module directly when the problem occurs... that would be a good indicator that the module is the problem. Otherwise, I would just go ahead and replace it. The part number is 10407669. It sells for ridiculous prices over $250 at regular parts suppliers, but it's available on ebay for $50-$60 and probably much less at your local junk yard.
There are ways to test the DRL module but they are somewhat complex (using a multi-meter - there is no specific tester available) and not always reliable when investigating an intermittent problem. If you really wanted to confirm, you could remove the radio and then tap the DRL module directly when the problem occurs... that would be a good indicator that the module is the problem. Otherwise, I would just go ahead and replace it. The part number is 10407669. It sells for ridiculous prices over $250 at regular parts suppliers, but it's available on ebay for $50-$60 and probably much less at your local junk yard.
Thread Starter
Staging Lane
Joined: Mar 2020
Posts: 65
Likes: 4
That sounds more like a problem with the DRL module which is mounted to the defroster duct directly behind the radio. It controls the switching of the front lamps between DRL mode and turn signal. There are internal relays which manage that switching. It's possible that the relay for the right side is sticking and failing to engage properly. Unfortunately, the internals of that module are considered "non-serviceable" by GM although the relays can be replaced if you're good with soldering on printed circuit boards.
There are ways to test the DRL module but they are somewhat complex (using a multi-meter - there is no specific tester available) and not always reliable when investigating an intermittent problem. If you really wanted to confirm, you could remove the radio and then tap the DRL module directly when the problem occurs... that would be a good indicator that the module is the problem. Otherwise, I would just go ahead and replace it. The part number is 10407669. It sells for ridiculous prices over $250 at regular parts suppliers, but it's available on ebay for $50-$60 and probably much less at your local junk yard.
There are ways to test the DRL module but they are somewhat complex (using a multi-meter - there is no specific tester available) and not always reliable when investigating an intermittent problem. If you really wanted to confirm, you could remove the radio and then tap the DRL module directly when the problem occurs... that would be a good indicator that the module is the problem. Otherwise, I would just go ahead and replace it. The part number is 10407669. It sells for ridiculous prices over $250 at regular parts suppliers, but it's available on ebay for $50-$60 and probably much less at your local junk yard.
I'll take em both out and post pics of the repair. What's with the PCB's n these cars ?
