I'm trying to track down an electrical gremlin in my Z28, and I'm completely out of ideas at this point.

What could cause the doors to lock when starting the car? Sometimes they don’t, but that’s rare—and it’s not even a factory option in the BCM.

Before the issue:
I removed the aftermarket alarm and rewired everything back to factory specs using the wiring diagrams from the service manual. I also added a keyless entry BCM (since mine didn’t originally have that function). I didn’t have this issue after doing that.

After the issue appeared:
I’ve already replaced the battery, cables, starter, 140-amp alternator, and BCM (and even fixed the solder joints on both BCMs). I also unplugged the lock switches. I checked for parasitic drain—nothing. All ground are clean as new.

I tried pulling the courtesy fuse—no door locks (which is normal). I also unplugged the C1 (green) connector from the BCM, and the doors didn’t lock either.

I even tried pulling the ignition fuse or relay (can’t remember which) and attempted to start the car to see if the doors would lock just by turning the key—but they didn’t.

If anyone has had the same issue and figured it out, please chime in!

Here’s a video of the issue:

 

No one have an idea ?

 

Sounds like you created a new security feature. Doors locked is a good thing.

 

Not my cup of tea, I not used to it and forget it everytime . And it's more a electrical problem than new feature 😂

 

Seriously, nobody ever had this issue ?

 

Actually, automatic door locks have a significant down side that makes them less safe than unlocked doors except in limited circumstances like particularly dangerous neighborhoods where car jacking or other threats are more prevalent.

Otherwise, in the much more common cases of being in a crash, the car catching fire, ending up in a retention pond (unfortunately far too common here in Florida), a medical emergency, or some similar situation, the locked doors will prevent bystanders from getting you out of the car. Most witnesses will not have the tools to break into the car and first responders may be unavailable quickly enough. The pocket knife/multitool I carry in my pocket has a glass breaking hammer tip, but I've never tried it and I'm not sure how effective it would be in an emergency situation... the average person wouldn't even have that.

 

This is beyond any symptoms I've heard of before. You have done an admirable job of diagnostics and eliminating the likely causes. Replacing the BCM eliminates it from being the source... the chances that a replacement BCM would have the same fault are impossibly small. The results of your other tests are as expected, but are good for informational purposes.

Do the doors re-lock after you manually unlock them with the ignition on? If not then you're looking for some momentary lock signal to the BCM when the ignition is first used. If they do re-lock then it's possible that there is a ground (lock) signal on the red/black wires between the BCM and the door lock switches - perhaps caused by the wire grounding out somewhere due to damage to the wire's insulation. You could unplug the green connector at the BCM and test for ground on the red/black wire. Under normal circumstances, there should be no connectivity to ground unless one of the door lock switches is activated.

The relationship to ignition is puzzling since the door lock system runs off the COURTESY fuse which is hot at all times (battery feed). Turning on the ignition should have no impact on locks unless the BCM is faulty somehow - but we've already eliminated that possibility. Do you still have the BCM without the keyless entry option? Does reinstalling that eliminate the problem? I'm wondering if the remote fob might be mistakenly signalling the BCM to lock the doors. If you don't have that original BCM, you could try putting your fob(s) in the microwave to block any signal and see if the problem goes away.

Those are the possibilities that come to mind initially. I'll keep giving it some thought and see if any revelations come to me.

 

Another thing to try is to unplug the door lock switches themselves. Try unplugging each of them separately to determine if one switch or the other might be the cause.

 

t’s the only time the doors lock without being requested; everything works perfectly except for that.

Just probe the red/black pin to chassis ground with an ohmmeter. Should I do it when starting, or when it’s off/already running?

I already tried the original BCM once, and it seemed to do the same thing. I should try again to get a fresh confirmation.

It would be my last idea too! That, and checking whether I accidentally connected something like the steering wheel control module or an aftermarket radio unit to the courtesy fuse. But I don’t think that’s the issue—I didn’t have this problem when I installed them.


This is the only topic similar to mine, but 2007 and no answers... https://ls1tech.com/forums/wiring-st...ck-bypass.html

 

Sorry, I'm not getting what you mean. Do the doors lock when the ignition is turned on or when turned to start? Do the doors re-lock if you manually use one of the switches after that initial automatic locking or do they stay unlocked then (i.e. are you always fighting to keep them unlocked after that first automatic lock)?

First test with everything off to establish a baseline. Then, duplicate the conditions that cause the automatic locking while monitoring your meter for continuity to ground on the red/black wire. Make sure you do this with the green connector unplugged (rather than probing the wire while plugged in) because you want to test the wire rather than its interaction with the BCM.

Can't hurt, but I wouldn't expect different results.

This note made me consider something else... is it possible that the previous owner installed an automatic lock module as part of the aftermarket alarm system? And is it possible that such a module might have been separate from the alarm brain and still be connected somehow?

 

It only does that when I start the car, like in the video: ignition on, nothing; then starting the engine and—BOOM—it locks. After that, I can unlock and relock it as much as I want using the switch, and it works normally. The issue only happens at the moment of starting the car.


OK I'll give it a try this weekend then

Not, it can’t. Actually, the aftermarket alarm was installed officially by Opel when the Camaro was imported to Europe, because the GM factory setup is too simple for insurance companies. So we have a 681 BAS BCM with all the components for keyless entry (except the BCM, so no horn or flashing lights).

But I removed it because Opel did a poor job with the wiring. I hated the remote, and they didn’t wire the hatch release. There were only two modules from this alarm, and I’ve cleaned everything out. I haven’t had the issue since then, so it’s not related to the aftermarket system.

The only thing that makes me think it could be a damaged wire or the door lock module is that sometimes it doesn’t lock at startup. Then, as time passes, the automatic locking appears almost every time.

 

Sorry, didn't watch the video (I hate YouTube with a passion).

Knowing that it only happens when the starter circuit is engaged, even if ignition has been on for a while, gives me something more to think about. Also knowing that it was a European import is helpful because I can go back to the service manual and have a closer look at the different schematics for export vehicles.

I'll let you know if I find anything new.

 

So,
I tried disconnecting both doors (one at a time), and each door locks the same way. I also retried with the switch unplugged, and it still locks. With both doors disconnected (and even the green connector unplugged), the BCM is still triggered (I can feel the relay in it just by touching the BCM case)

Here’s a new video: I unplugged the fuel pump relay and both bank ignitions just to let it crank. You can hear the lock system activating every second, like someone is pressing the switch repeatedly like a maniac.

 

I tried starting with both of my remotes without batteries, instead putting them in the microwave, and I still get the same issue with the 691 UPL.

I also have two old BCM 681 BAS units from my previous V6, as well as the Z28 without keyless entry. With the V6, the security light comes on (which is normal since the key value is different), but it confirms that I was very lucky when I bought the 691 UPL without knowing whether the registered key value was correct. It started right away when I swapped them.

With the old 681 BAS BCM, there’s no issue at all. Just no keyless entry 😭

So the problem seems to be inside the BCM itself… Now the challenge is figuring out exactly where 😆 Because I resolder every pins of the 5 relays yesterday. So there's a current leak somewhere in it. Maybe I can try to put the relays from the old BCM 681 to the "new" 691

 

Find it!

Today, I decided to trace the BCM PCB and use a spare unit (which doesn’t have the issue, but unfortunately also doesn’t have keyless entry) to check the “lock all input” pin.

And tada—my BCM with keyless entry doesn’t have continuity between those two points (while the other one does).

I soldered a thin copper wire between them, and now there’s no more false anti-carjacking.

 

That's very impressive! Repairing (rather than just replacing parts) has become a lost art... good job!

 

Yes, import an used BCM to France and will probably need to buy a new set of keys (if it doesn’t match mine). It might cost more than it would take to actually find the issue

Thanks for the help! If I had known I could troubleshoot it easier just by unplugging the fuel pump relay and door locks, it would’ve been fixed ages ago

You can compare the 681 BAS BCM for European market to a US 691 UPL BCM on the pictures above too