DIY: Replace dreaded steering-lock on 2009s and early 2010s.

Originally Posted by wstar

It's listed as both an input and an output for the BCM. It seems definitely sure that the BCM is who sends that little pulse train against a 12V background to send LOCK and UNLOCK commands, as an output. I misunderstood earlier that the pulse train came from the lock module.

What really makes no sense is how any of this could be an input back to the BCM. Maybe it's mislabeled (from my point of view), and the BCM drives it at +12V while LOCKED, and 0V when unlocked for 15+ seconds, and whenever it wants to send a command, it applies the +12V (if unlocked before) and then sends the pulse signal.

I guess someone would have to figure out what the manual means by clipping onto this with a scope (or really, even a multi-meter would do, since the only complex bit is already documented in the diagram above).

Originally Posted by ChrisSlicks

Not sure that you would capture the pulses with a multimeter, they appear to be only 1ms in duration at about 75ms, 35ms, 12ms apart respectively, definitely the job for a scope.

Originally Posted by wstar

Well what I mean is, we don't really have to capture them, since they're documented and they have to come from the BCM because there's no other way it's signaling the module to make the change.

What I don't understand is whether the lock module also supplies voltage to this wire at times to provide feedback to the BCM or something.

One way or another, a replacement would need: a cheap microcontroller to sense the command pulses on the communication line and update a little NVRAM state indicating whether the fake lock is currently stuck-on or stuck-off, the microcontroller would need to be powered on any time either of the power supply pins lights up and provide S1/S2 feedback based on NVRAM, and possibly voltage feedback on the communication line as well.