No Brake Lights After BCM Swap, Advice Wanted
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Junior Member
Joined: Nov 2025
Posts: 8
No Brake Lights After BCM Swap, Advice Wanted
I need help getting my BCM situation solved, I installed one from Ebay and everything works but the Brake Lights.
About a month ago, it rained pretty heavy for about a week and I went out to the H3 and it wouldn't start. It was acting a little bit like the battery was dead, so I didn't mess with it till after work, and when I did I found a huge pool of water in the passenger floor board from where the sunroof drain had failed. Naturally, it was dumping water straight into the BCM. We removed the BCM, and it was like a bottle of water, the whole thing was just full of it. So we took it and dried it out for a few days, but when we put it back in the starter would engage pretty much on its own, the left blinker and horn were stuck on...and a whole other list of problems. We read online that the BCM's were fairly interchangeable, so we ordered one on Ebay that had a part number similar to mine, though the BCM in my 2007 H3 has the part number smeared and I can't exactly read it.
Naturally, the new BCM didn't agree with the Passlock, but I did the ritual of trying to start the truck, letting it sit for 10 mins till the security light stopped, then after 10 seconds trying to start it again again, then waiting another 10 mins for the light to go off. After 3 or 4 cycles of this it worked. The Passlock was satisfied and the truck started just fine. Everything worked except it now had lights on the dash associated with the ABS. We drove it a bit and then found out the brake lights weren't working... The check engine lights are for the EBCM (electronic brake control module), and I can't find a way to reset it.
What do I need to do to fix this? I think it is an issue with how this BCM talks to the rest of the truck.
I do have a GM Tech II and am very experienced with the GMT800 and GMT900 trucks, but this is the first GMT300 truck I've had anything to do with.
Can the Tech II even be used to reset this? Do I need a different sort of programmed? Can used BCM's not be reprogrammed at all? If so then why are they even being sold? Is there a weird ritual to reset the EBCM, like how you can turn the light switch 3 times with the parking brake on to reset the tire pressure monitors?
About a month ago, it rained pretty heavy for about a week and I went out to the H3 and it wouldn't start. It was acting a little bit like the battery was dead, so I didn't mess with it till after work, and when I did I found a huge pool of water in the passenger floor board from where the sunroof drain had failed. Naturally, it was dumping water straight into the BCM. We removed the BCM, and it was like a bottle of water, the whole thing was just full of it. So we took it and dried it out for a few days, but when we put it back in the starter would engage pretty much on its own, the left blinker and horn were stuck on...and a whole other list of problems. We read online that the BCM's were fairly interchangeable, so we ordered one on Ebay that had a part number similar to mine, though the BCM in my 2007 H3 has the part number smeared and I can't exactly read it.
Naturally, the new BCM didn't agree with the Passlock, but I did the ritual of trying to start the truck, letting it sit for 10 mins till the security light stopped, then after 10 seconds trying to start it again again, then waiting another 10 mins for the light to go off. After 3 or 4 cycles of this it worked. The Passlock was satisfied and the truck started just fine. Everything worked except it now had lights on the dash associated with the ABS. We drove it a bit and then found out the brake lights weren't working... The check engine lights are for the EBCM (electronic brake control module), and I can't find a way to reset it.
What do I need to do to fix this? I think it is an issue with how this BCM talks to the rest of the truck.
I do have a GM Tech II and am very experienced with the GMT800 and GMT900 trucks, but this is the first GMT300 truck I've had anything to do with.
Can the Tech II even be used to reset this? Do I need a different sort of programmed? Can used BCM's not be reprogrammed at all? If so then why are they even being sold? Is there a weird ritual to reset the EBCM, like how you can turn the light switch 3 times with the parking brake on to reset the tire pressure monitors?
Thread Starter
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Junior Member
Joined: Nov 2025
Posts: 8
Also, there was some corrosion on a few of the terminals in the wiring harness going to the BCM. Is there a chance its just a corrosion issue and the BCM is actually working properly?
Everything works except for the brake lights and indicator lights on the dash for when the blinkers are on (the blinkers still work, just the arrows aren't lighting up).
I wish I knew if the BCM was actually communicating correctly... the only clue I have to this is that when the TECH 2 data stream is pulled up it does accurately tell me when brake pedal is being pushed... which makes me think it may be a connection issue sending power back to the brakes...
The plugs are corroded just enough to make me wonder, but not so bad its convincing...
Everything works except for the brake lights and indicator lights on the dash for when the blinkers are on (the blinkers still work, just the arrows aren't lighting up).
I wish I knew if the BCM was actually communicating correctly... the only clue I have to this is that when the TECH 2 data stream is pulled up it does accurately tell me when brake pedal is being pushed... which makes me think it may be a connection issue sending power back to the brakes...
The plugs are corroded just enough to make me wonder, but not so bad its convincing...
Senior Member
Joined: Feb 2021
Posts: 264
From: New Mexico
I'm not a BCM expert, so will let other's chime in on interchangeability of BCMs. I've seen some posts in these forums with folks having a horrible time getting both new and used BCMs to work in their vehicles, so it seems they aren't all plug and play with each other.
Did you check fuse 20 in the fuse box for the rear turn and hazard lights. If that is blown you will have no rear brake lights, no rear turn signal lamps, no rear hazard lights, and the turn indicator lights in the cluster won't work either. The high mounted stop lamp is on another circuit so it should still work.
No matter, if you saw corrosion in the connectors I would highly recommend you use CRC electronics cleaner to clean that wherever you see it. Every electrical gremlin on my truck has been from either connector corrosion or battery/battery terminal issues. It wouldn't hurt to also clean the old BCM circuit board with it and see if that resolves the original issues.
Did you check fuse 20 in the fuse box for the rear turn and hazard lights. If that is blown you will have no rear brake lights, no rear turn signal lamps, no rear hazard lights, and the turn indicator lights in the cluster won't work either. The high mounted stop lamp is on another circuit so it should still work.
No matter, if you saw corrosion in the connectors I would highly recommend you use CRC electronics cleaner to clean that wherever you see it. Every electrical gremlin on my truck has been from either connector corrosion or battery/battery terminal issues. It wouldn't hurt to also clean the old BCM circuit board with it and see if that resolves the original issues.
Senior Member
Joined: Dec 2019
Posts: 188
I just went through this. Don't yet eliminate the actual brake switch at the pedal. Simple check. Unplug the connector and short the connector.
I was confused because my middle brake light would light up, but not the tails lights. Ended up being the switch anyway.
I was confused because my middle brake light would light up, but not the tails lights. Ended up being the switch anyway.
Super Moderator
Joined: Jul 2007
Posts: 13,056
From: Boat Town USA MI
Fix your leaking sunroof drains. Dry everything out double super duper good. Then start cleaning your corroded electrical BCM Harness. If it still does not work, you may need another (not water soaked) BCM.
Senior Member
Joined: Apr 2019
Posts: 3,181
From: BX NY North East
to flash the bcm you would need the tech2 if thats what you have available and a PC to download the calibration files to the tech 2 then you can flash them into the bcm as a passthrough if near the pc or store the calibration in the tech 2 if in a remote location like the "boonies".
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Junior Member
Joined: Nov 2025
Posts: 8
to flash the bcm you would need the tech2 if thats what you have available and a PC to download the calibration files to the tech 2 then you can flash them into the bcm as a passthrough if near the pc or store the calibration in the tech 2 if in a remote location like the "boonies".
Is there certain software I need on the PC? Where would one get the files?