I’m a long-time H3 owner based out of Reno, NV, and like most of you, I’ve spent way too much time sitting in parking lots waiting for the 10-minute "Security" light lockout to reset. After looking into the factory Passlock II logic, I realized the "relearn" is just a band-aid for a mechanical sensor that eventually fails for good.

I decided to deep-dive into the BCM handshake logic to see if I could satisfy the security requirement electronically rather than mechanically.

I’ve successfully engineered a setup that mimics the exact ignition sequence and resistance signature the BCM needs to see. It provides "Start Permission" to the ECM for fuel and spark without having to tamper with the onboard computers or re-flash the BCM. As a bonus, it allowed me to modernize the truck with a Push-Button Start and PKE (Passive Keyless Entry).

It’s been rock solid on my H3 and a few other local GM trucks (Colorado/Canyon) that use the same Mux ignition logic. I've even figured out how to keep the radio/accessories off during remote starts so it doesn't draw attention.

I'm not looking to clutter the boards with a sales pitch, but I know how frustrating this specific H3 quirk is. If anyone is tired of being stranded by their ignition cylinder and wants to know more about how I bypassed the sensor logic, feel free to reach out or drop a comment.

Happy to share what I've learned!

 

Never had a Passlock issue in any GM vehicle yet. I always have a can of CRC Electronic Cleaner and know where the ignition switch is.

I am sure others would appreciate it.

Welcome and thank you.

 

I tried to send a private message but couldn't. I would be interested in your solution.

 

I would be interested in info.