2004 Pontiac Montana Doorlock Issues

Okay, we do a whack pile of Montannas and Transsports. Lady comes in yesterday, and her van isn't locking with the 591XV anymore. Unlocks, disarms, etc, but will not lock to save it's life. To make things more interesting, the factory switches will also not lock the doors... unlocks them just fine. The strangest part? Factory fobworks like a charm. Starter has been in the van, and working flawlessly for the better part of 8 months, brain is outputting a lock pulse like it should, everything. Metering at the switch, I get nothing.... open circuit on the lock side to ground. (unlock.... resistance of a relay coil, which makes sense). 1) Where's the BCM? 2) Driver's or passenger's master, or does it really matter? This is really wierd, vaguely remember another van doing the same thing 4 or so years ago, be dammned if I could remember what the problem was. Being as it is hardcore starter season here right now, the thought of spending several hours tracking down something which may be a GM problem does not makeme overly enthusiastic about telling her "Sure, we'll drop everything and fix your problem". Any ideas? Anyone? Gus Wherever I go, that is where I end up......

What year is the vehicle? Do they lock when you put the key in the door and lock it manaually (central locking)? J Rilla

Owner/Installer

The BCM is above the passenger's kick panel. Check the light blue lock wire at the BCM to see if it getting power when either lock switch is pressed. It is in position A7 of the BCM's larger plug.sparky

Oddly enough, central locking with the key in the door is the one thing I forgot to try, unfortunately. I'm just not seeing anything at either switch, so this is what is making me suspect the BCM, or possibly a wiring issue somewhere. The van in question is an early 2004 (Build date of March 2004), no factory content security, just RKE. Still rather puzzled by this, as this is the first I have seen do this in a while, and the last one, I never did hear the outcome of it(IE: we didn't get a bill from the dealer or mechanic on it, nor did we get chewed out as a result..... therefore, not my problem) Still puzzled, and fighting a wicked case of the flu, in the heat of starter season..... whooppee! Gus Wherever I go, that is where I end up......

Bringing this one back up.... standing beside it right at this moment. All wiring checks out fine. No opens all the way back to BCM. Unlock works perfectly, 12V showing on the white wire, when sentto ground, doors will unlock. They will also lock only with the factory keyless entry just fine. There is a lack 12V on the blue lock wire at the BCM.... something is open inside the BCM.... I began tracing the circuit, gave up after half an hour of a very bright light and playing "goes through the PCB here.... flip over, goes back through here, flipover.....etc. etc." There is a problem somewhere in the circuit isolation sideof the doorlock relays (isolates the switch inputs from the keyless entry portion of the relay drivers... basically, SMT caps and diodes) I am not going to spend hours troubleshooting a bunk BCM without a schematic.... the van is on warranty..... I still can't really see it it being anything we did. The problem showed up approx. 7 months after we did the starter.... and I really can't see how duplicatingthe switch function is a problem. This is not the first Montana/Venture/Silohuette that I have done, probably the 50th or so in the past 5 years. This is the first time I have seen this particular issue, so this is rather perplexing to say the least. Gus Wherever I go, that is where I end up......