Doorlocks fail when cold

[vljenewein]

Here is the details: 1993 Park Avenue Ultra with remote key fobs.
This is what happens: In the summer when it's warm I get in start up the car and pull it our of park and door lock. I put it back into park and doors unlock. Key fob remotes work as normal. Press unlock once and drivers door unlocks. Press again and all door unlock. Trunk opens as it should with fob or with dash switch. All seems normal and happy.

Now comes fall. Cooler temperatures. Get up in the morning, temps now in the low 40's. Start car, and when you pull it of park into gear, no doors lock. Key fobs cease to operate. You put it back into park and no sounds either from trying to lock or unlocks. Turn off engine and remove key. Remotes still don't work. Sometimes if it does happen to lock the doors, then it won't unlock the doors when put into park. Wait about 30 seconds, hear a slight "ting-ting, ting-ting, ting-ting" and often the door remote locks will work. Unlock and lock, trunk also opens if pressed.

I've replaced the Body Control Module, and the door lock control module ( the one thing with about 8 or so wires running to it that you can hear and feel 'operate' when you lock/unlock the doors). It's under the right side dash kick panel, up close to the fuse block.

This only happens when the temperature is cold. Winter is worst. Summer all things work as normal and nothing seems out of place.
Has this ever happened to anyone else out there? If so, what was the cause of this?

Very perplexing problem. Also does the BCM control the rear window defroster? Seems when it's really cold that the rear window defrostere does not work (handy huh??). When the door lock/unlock things are working.. ie when it's warmer, it does work and put voltage through the wires in the back, and defog the rear window. What else does a BCM control??

[parkavenuechrome]

This is a fairly involved one. I would have to say that you probably have a sticking relay somehwhere that sticks worse when cold. as far as the defroster, check the fues and window wiring. I To have issues with winter defrost and I would have to replace the entire rear windows to get it repaired.

[vljenewein]

Interestingly, since I replace the Body Control Module the rear window defroster, did work this cold chilly Monday morning. I could see the ice melting on the lines as I was scraping the side, and front windows. But, alas, the door never locked when I pulled out of park, and remained so, disfunctional, until a while later when I parked.. warmed up a bit inside by then.

[parkavenuechrome]

mine does this at times, where it doesn't open the doors when i go to park.. Its a relay that hangs occasionally.. I wouldn't worry to much about it.

[vljenewein]

Yea, it's more irritation than safety, that's for sure. However, not only do the door not unlock/lock but the actual electrionic part of the door lock on the doors ceases to function along with all functions of the key fob, including opening trunk, lock/ and unlock. It sort of makes you "locked" in and unable to unlock unless you physically move the locks themselves.

[Jed Rule]

The door lock relay controls the 4 lock motors. That's the only part that has the same function whether triggered by the lock switches or the RAC module. On my 95 the relay is supposed to be under the driver seat. This could be your problem. Maybe it got a little wet under there at some time (considering how well the door gaskets seal).

[vljenewein]

Thanks Jed! I believe I've found the relay, and it's under the dash on the passenger side, near the fusebox, etc. If you place your hand on it and lock/unlock the doors you can feel the relays clicking. Unplug it and no doors lock or unlock. Swapped out mine with my wife's Chevy Lumina, and works ok while it's warm but get it cold and it's like there is no signal getting to the control module. (it's rectangular in shape with about 8 wires)

More important!! I should start a thread about this, but will update here a bit, as I do NOT think this new problem is related to the BCM, but ya never know.

Last couple of days my speedometer has quit working, intermittently. Starts back up again and I think, hmmm rather odd, gear must be getting worn. Come to find out in my shop manual it's covered in the ESM *Electronic Service Manual , which I don't have. So... it must be electronically controlled and not so much by gears.. BUT.. when in town tonight, I lost the speedometer AND the transmission slipped. Pulled over and turned it off. It repeated that same thing again within a few blocks and I pulled into a parking lot with lights. Fluids all checked ok.

Drove toward home, and all is working as normal.. speedometer, transmission shifting all ok.. Stopped for gas and when I pulled out, I gave it some gas and the transmission slips out of gear again, and the speedometer goes back to zero. Stayed that way the rest of the 4 miles home. BCM does not control the speedometer and transmission does it??

[pirho451]

Come to think of it. my '93 PA does the same thing. I snagged a couple of relays from the BCM of another one in a salvage yard, but haven't had the time to work on swapping them out.

[Jed Rule]

The RAC module and the door switches for the locks trigger the lock relay on parallel circuits. If neither work there must be a fault in the power to or from the relay. There should be 12v on the orange wire to the relay. The white wire triggers the unlock side of the relay, the lite blue wire triggers the lock function. The tan is the output to unlock the doors and the grey is the lock. It should work with the door switches regardless of the RAC. Maybe there is a weak ground on the black wire from the relay that opens up when cold. You can check this with a test light.

[vljenewein]

or a cold solder joint somewhere. I had a vehicle one time that worked great WHEN it was cold but when warmed up would die at stop signs. Kicked the interior module one time and it straigtened out (it was on left side Driver side - pickup). Took it apart and looked VERY closely and there was a crack around the solder joint. When it was cold it made contact, when warm the crack spread the connection and it would die. Resolders and good as gold.

[vljenewein]

Thought I'd add some addiitional perplexilng information, or perhaphs it's vital information for the diagnosis...

When I drive the PA when it cold out, and put in in park AND the doors don't unlock, they also don't unlock with the remote key fob, OR the buttons for lock / unlock on the side of the door. Nothing unlocks the car except manually lifting the unlock/lock bar.

Now the really odd part. I get out of the car, reach behind the drivers seat and unlock the left passenger car door, and the locks now mysteriously work!*(carry my briefcase in the rear seat area). The remotes work, and the buttons on the doors themselves now work. Won't work before you open that rear door. Odd huh?

[vljenewein]

Whoa, did I find something really odd this morning!! I decided to turn off the "twilight sentinel" on my 93 PA Ultra. So, instead of the headlights comming on or even having it on (even though it was light outside), the doors locked and unlocked perfectly!! It was really cold this morning, down in the mid 30's and usually this problem will show up around upper 40's to low 50's.

I left the automatic light "sentinel" off all day and never once had any problems with the door lock relays when moving form park to Reverse/drive and back into park again. None. Not any.

The only reason I tried this was thinking that there needed to be extra voltage to work the relays properly. SO... I gave it a shot. really perlpexing isn't it??

[primemover]

For what it's worth, this sounds almost identical to a puzzling problem that I had on the 93 PA Ultra. In my case, the locks would work until a minute or two after I started the car on cold days. To make a long story short, the ultimate problem proved to be the 30 amp auto reset thermal circuit breaker which feeds power to the door locks and the heated rear window and the heated outside mirrors. When the rear window defogger is turned on, the load through that breaker is 30 amps and the breaker will trip in short order, following which the locks don't work until the breaker cools down and resets. The fix was to move the wire for the power feed to the outside mirrors heat to another fused circuit. The breaker now doesn't trip when using the rear window defogger and the locks allways work.

[vljenewein]

Primemover, what you describe is what I am experiencing. I notice that when I turn on the rear defroster for a short period, the door locks won't work. If I don't mess with it, I don't seem to have the problem as bad. Where is this 30amp breaker? Perhaps I can replace the breaker as it may be getting old and tired. 93 buick PA Ultra but I don't have heated mirrors, at least none that I've noticed. Thanks
Vern

[primemover]

Originally Posted by vljenewein

Primemover, what you describe is what I am experiencing. I notice that when I turn on the rear defroster for a short period, the door locks won't work. If I don't mess with it, I don't seem to have the problem as bad. Where is this 30amp breaker? Perhaps I can replace the breaker as it may be getting old and tired. 93 buick PA Ultra but I don't have heated mirrors, at least none that I've noticed. Thanks
Vern

The breaker is in the fuse box (which flips down) to the left and above the brake pedal (my foot sometimes touches it when I'm driving). The fuse box map shows it. I thought all the Ultras with rear defogger also had the heated mirrors. I tried changing the breaker too, thinking the same as you, but it still had the problem. I couldn't find a breaker rated higher than 30 amps, but that would be an easy fix if you can find one - or if you're brave you can solder a shunt wire around the breaker. I measured the current draw on that circuit and found it to be 30 amps when the rear window defroster on - got it down to approx. 20 amps by removing the wire feeding the mirrors. I understand some Buick dealers have also dealt with is problem by moving the mirrors to another circuit. Anyway, it worked.