Firstech CM6200: doors don’t unlock

I've got an 06 Cobalt (Auto) with the CM6200. It's programmed to a 2 way remote & everything works (start, 2 way confirm start, stop, lock, unlock trunk) EXCEPT for unlock.

I hear the CM6200 "click" but the doors stay locked. The 2 way remote THINKS it's unlocked (unlock icon) but no, it's not!

On the wiring diagram I see Pin 4: Blue "(-) 250mA Unlock Output". Should it be as simple as tracing that wire & making sure it hasn't come loose?

Maybe, and maybe not.

First question is : Did it ever work?   Perhaps the original installer was a DIYer and couldn't figure
it out. Or if it did work and then quit...

That car has a one-wire door lock system. If the original installer did not use a special full function
bypass module and wired the CM6200 directly to this vehicle wire shown below, you could follow the
Blue Unlock wire to see where it goes. BUT it will have a 1.5K ohm, 1/2 watt resistor added to it
somewhere. Additionally, the installer could have joined the Unlock wire and the Lock wire after
this resistor and just had one wire going to the vehicle shown below. It is possible that a real good
installer would use relays on the lock wires due to the possible current draw of the one-wire lock
system. Every installer will do it differently. ( I use a full function bypass module on those cars. )

WHITE (-)    DRIVERS KICK PANEL OR BCM, GRAY 72-PIN PLUG "X1", PIN 7 or Pin 6

If the installer used a full function bypass module like the Fortin INT-SL+ or CAN-SL2, then the CM6200
lock wires will go to this bypass module ( with no need for the 1.5K resistor ). It might even be possible
that the installer used a bypass module and went D2D between them and none of the CM6200 lock wires
or trunk release wire was needed.

My guess is that you will find the Blue Unlock wire run to the car and hopefully an issue with a connection
somewhere. Maybe the installer didn't properly solder the connections and a twist connection at the 1.5k
ohm resistor came loose.

Anyway, find the CM6200 and see if the lock wires are used and where they go.

-------------
Soldering is fun!

Thanks for the informative reply, just getting back to this now.

I have no idea if it ever worked, it's been like that since I bought it. I can confirm that the blue (unlock) & blue/black (lock) wires from the "output connector" wire block are how it's set up to work.

Like you were saying there is a relay involved but it looks wrong. Here is how it's wired:

87 - disconnected
86 - Red wire from CM6200 (+) 12v Constant
87a - blue/black (lock) from CM6200
85 - blue (unlock) from CM6200
30 - to white wire on connector C1 on BCM (wiring diagram shows as door lock/unlock signal pin 6 or 7)

Not sure where along the line the resistor is (yet)

I've been reading up on relays and this doesn't make any sense...I see how 30 can connect to 87a (lock) and work, but 85 (unlock) is essentially connecting to 86 which is looping back to 12v power which sounds like a bad thing? What's the proper way to wire this?

Ok, good info. You did say the CM6200 Lock command did work and lock the doors. Next next step is
to test and see if a CM6200 Unlock command makes the relay energize. Place a finger or two on the
relay and press Unlock. Do you feel it click? Is yes, the CM6200's Unlock pulse is OK and can energize
the relays coil. The next test would be to connect relay Pin 87 to Chassis Ground with a jumper wire.
Try an Unlock command again, this time the vehicles doors should lock. If that happens, all you need to
do is obtain a 1,500 Ohm, 1/2 Watt resistor and connect it to the relay Pin 87 with the other end going
to Chassis Ground.

As a final thought, check the relay to see if it has internal coil quenching or a diode added between
Pins 85 and 86. This diode is to protect the CM6200's Unlock circuit from the relays coil collapse pulse
that could exceed 200V DC. Several successive Unlocks from the CM6200 could generate such a pulse. If
there is no diode found, I would get a 1N4004 or 1N4007 diode and solder it across Pins 85 to 86 with
the band towards Pin 86.

-------------
Soldering is fun!

Yes, the unlock command makes the relay energize. Nothing happens but it does energize.

Next thing i'll do then is connect 87 to ground.

Regarding the internal coil, I don't see anything added internally, looks unmodified to me. I should mention that the fob has the same button for lock & unlock so maybe they used that kind to mitigate that scenario?

Some relays have internal coil quenching diodes. They are marked on the relay body in the pin
diagram embossed in or printed on the relay. Most don't, so a diode is added externally to the
relay or the 5 wire harness.

-------------
Soldering is fun!