Enclave has a mind of its own
Hey guys, got a cool one here. I hope it will make sense. This 2019 Buick Enclave came in for a weird complaint. After exiting the vehicle the door locks, low beam headlights, and hazards would flash or cycle on there own. The interesting thing to note is this only happened IGN off, car powered down. A full vehicle code scan was done with GDS2 with no codes at all. It took me a minute to get a game plan together as how to approach this diag. I narrowed it down to 3 different scenarios. I have added a video of the symptoms to give you an idea of what is happening.
#1 At first glance you could almost say that this is an unwanted remote transmitter activation from say a malfuntioning keyless entry antenna. This car is a push button start. The immobilizer an keyless entry antennas are hardwired to the Keyless Entry control module who buses the info to the BCM over a CAN network. Going thru data in the Keyless Entry module everything looks normal when the problem occurs. To eliminate an antenna or Keyless Entry problem I pulled the fuse to the Keyless Entry Module to take it offline. There was no change in the symptoms.
#2 There have been TSBs from GM in the past of unwanted lock an unlock activation through Onstar. To rule this out I pulled the fuse to the Telematics Communication Interface Module. Again no change in the symptoms.
#3 The BCM receives the inputs from the interior door lock switches and controls the door lock actuators via highside drivers. So now I am going to focus on the BCM. I decide to watch data for the interior door lock switch inputs on GDS2 scan data. Sure enough, sometimes when the symptom occurs the drivers door lock switch PID shows Lock or Unlock as though you pushed the switch even though no one is pushing it. Okay cool , unplugging the drivers door harness there is no change in the symptoms. The door lock switch circuits are a very simple circuit. The BCM sends a ref voltage out on all the signals and when you press a switch it pulls the respective signal to ground and the BCM responds with the appropriate command. Here is a schematic.
I decide to go straight to the BCM and connect the PICO to all 4 door lock switch lock and unlock signals to see if anything is happening on the circuits. Here is a PICO screenshot when the problem occured.
Wow, thats not something you see everyday! All 4 door lock signals being pulled to ground at exactly the same time?? After this I put the PICO on the Hazard and headlight switch signals. They are the same circuit design as they door locks. They were getting pulled to ground at the identical time as the door locks. I didnt post a PICO file of that, you will just have to take my word for it. At this point it looks like an internal BCM problem. However I want to be right the first time so lets think about this logically. When a switch is pressed the line gets pulled to ground, that is the circuit design. So lets say the pass door unlock switch signal was actually shorting to grounding intermittently on the dash somewhere it would not backfeed into all those circuits. Unplugging the BCM connector that houses the door lock switch circuits shows no erratic voltage on the PICO now. However the door locks ,hazards and low beams still cycle. Okay now I feel confident that the issue is inside the BCM. I pull every fuse to the BCM and the switch signals still pull to ground! I think wow there must be a capacitor inside the BCM that is still able to shoot out power and its somehow shorting into these switch signal circuits. I pull the BCM out an pull the board out of the case. After looking for awhile I find this hidden under the corner.
Wow now I can breathe a sigh of relief. I have no idea were this little bit of corrosion came from. The BCM is mounted above the trans tunnel under the HVAC case, in front of and below the center console. There is no sign of water intrusion. The car doesnt have a sunroof and I see no staining and completely dry floor pans. Anyway a new BCM fixed this car. This one really tested me for sure. However I am glad I followed a systematic approach and didnt let the symptoms or year of the vehicle deter me. Thanks for reading hope you find it helpful!
Well done. I think you did a very good job of explaining your steps and posting it in a way that can help others!
Nice case study. I think the corrosion could be from water condensation. Moist air and temperature changes. Just a guess.
Awesome diagnostic, definitel help me and others in the near future. Super glad you resolved the problem. Thank you.
Awesome stuff man. Just a question though, being a '19 why wouldn't it have been at the dealer for this?
I am at the dealer. I started a mobile diag business 4 months ago that's why that's my name business name on my profile.
Right, I see that your business name is on your profile. I was just wondering why someone that doesn't work for the dealer is doing warranty work. Thats all.
Sorry I still work at the dealer fulltime. Still building a customer base with ….
Thank you for sharing. It is great to see how you handled the situation when "no codes" are present.
one to remember for sure. The part I'm gonna remember most was the step by step logical path you took to the answer. well done thanks for sharing !