Not enough power to the door lock actuators

jwebster · Post by **jwebster** » 13 Sep 2011, 19:50

I have a 2000 S70 glt/se turbo. I have 4 locks not getting the job done when the power lock button is pushed for both up and down. I thought that all 4 were broken so I started to try and replace them. However, the more research I did, it is most likely not all 4 broken at once. It is probably either a blown fuse or the actuators aren't getting enough supply of power. I'm not sure what fuse number it is for these locks, I'm guessing the number 2 in the supp. fuse box. Also how do I check to see if the circuit is good for the supply to the actuators? I'm thinking it's the vgla. The horn sounds real weak, and one time recently, the alarm went off accidentally and it sounded pitiful. I'm thinking that is connected to the weak response I get from pushing the lock/unlock buttons.

Post by **BEJinFbk** » 13 Sep 2011, 22:03

Actually, there IS a really good chance they're all toast.
Pretty common failure item. They've been at work for 11 years.
I think I've seen one post about bad relay contacts in the central
locking unit, ( and IIRC, that only affected the drivers door ),
but literally hundreds about dying actuators. Sorry...

I would consider getting popping a door panel and getting a
meter on the door lock motor if you really want to be sure.
But don't be surprised if there's plenty of voltage there.

The horn? That's almost always a loose nut in the center of the horn.
Tighten it up and hit the big red PANIC button!

Post by **jimmy57** » 13 Sep 2011, 22:35

Volvo and others have used a PTC resistor as a sort of thermal overload for lock motors. It was inside the lock actuator and was a disc a bit smaller than a dime between two contacts series to the motor. The PTC will heat from load of motor and resitance goes up several hundred ohms and effectively shuts off current flow.
I looked and looked for the PTC in the couple of lock motors I replaced. I checked power supply to the locks during function cycle. I attached a small 12V dc computer fan and it would start with a jump when I locked or unlocked doors so I knew that power supply was not the issue. I finally found the PTC recently. I was going to do a photo how to but I haven't found the time yet.
The PTC is inside the small motor inside the lock unit. You have to use a Dremel or other mini cutter tool and go around the lack actuator case so it will open. Then you will see the small electric motor. Then you snap motor out of its perch and pry the two tabs that hold the end cover of motor on. The PTC is maybe 3mm by 4mm and wedged into a pocket between the integrated contact on motor and one of the brushes. The PTC will be corroded a bit and that causes it to have resistance so the motor never gets full power and the PTC heats quickly and cuts current down and the motor wimps out before it completes the cycle.
I hammered a piece of 10 ga. copper wire flat and cut it and pushed the copper piece into the pocket where the PTC had been. I re-assembled the motor and then inserted it and epoxied the lock actuator back together and that lock works great.
The problem will hit locks on the car at more or less the same time in a lot of cases.

Post by **boosted5cyl** » 13 Sep 2011, 23:52

With the other electrical symptoms, I wonder if its worth your while reconditioning the B+ terminal?

V70 terminal repair main fuse box diy

jwebster · Post by **jwebster** » 18 Sep 2011, 07:35

Jimmy57, that was dope. That just saved me about $120. I just fixed all four locks, and they are going strong! If anyone does this rather than replacing them, just a few tips. Use something to bond the case back to the engine if you have to break the tab to get the case off. And epoxy didn't work for me. But if you jam a pick around the perimeter where they assembled it, the cover should pop off. And if you do this the case will just pop right back on when you are done. Do multiple points of insertion. Definitely replace the PTC, I tried just cleaning it and that definitely was not enough. Thanks again bro!

gilhuly · Post by **gilhuly** » 18 Sep 2011, 08:57

That is some awesome insight. Thanks for posting it Jimmy. I don't think I've ever seen a refernece to this before.

FCPEURO · Post by **FCPEURO** » 18 Sep 2011, 09:44

+1

Never would have thought you could fix that PTC resistor. I bet a lot of people have just replaced the motors because they did not know what they could do to fix the issue. Now they do.

Post by **BEJinFbk** » 18 Sep 2011, 13:09

Not to knock Jimmy here, but it's worth keeping in mind that
when this procedure is performed, a safety device is being bypassed.
The PTC is there for a reason. Replacing it with a chunk of copper is
not much different than replacing a fuse with a penny. Just sayin'...

whoa · Post by **whoa** » 18 Sep 2011, 14:27

Does the thermistor have any writing on it that would help identify its value in ohms?

Post by **BEJinFbk** » 18 Sep 2011, 15:42

whoa wrote:Does the thermistor have any writing on it that would help identify its value in ohms?

That's an excellent question! If we could nail down the current rating for these,
a replacement would be a much better way to go than a bypass.

For anyone interested, here's a little more info on PTC's:

http://www.electronics-manufacturers.co ... n-257.html