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vehicle: 2011 Cadillac CTS 4 3.6L

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7 years 5 months ago #2397 by ericblack
Vehicle: 2011 Cadillac CTS 4 3.6L. with e-latch locking system. Sympton: drivers door won't open externally, but will via internal door handle. Fix: replaced external door switch with new micro switches.

Question: How do you test the door latch? I applied power and ground to dk-g and tan wires (see attachment) and the latch won't operate. I tested the passenger side (known good) in the same manner and still no latch operation by applying power and ground. The only way I can get the latch to operate is by shorting the two micro switches in the exterior door handle mechanism; however, why can't I apply power and ground to the latch and make it operate? The drivers door module pulses the door latch via two relays (see attachment). I can barely see the pulse on my power probe. The pulse seems to be so fast that my test light won't even light (or maybe my bulb resistance is too low). Regardless, it is very difficult to see the power and ground being temporarily supplied. So, looking at the schematic (see attached), the latch is a simple motor; but, I apply power and ground in both polarities and nothing happens? Why? Any ideas?
Attachments:

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7 years 5 months ago #2398 by ScannerDanner
There is clearly something else in the motor assembly. They even call it a "driver".
Mechanically, does that motor latch and unlatch? In other words reverse polarity? The diagram seems to show a constant ground on one side but it's after that other piece in that motor assembly

Don't be a parts changer!

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7 years 5 months ago - 7 years 5 months ago #2400 by ericblack
Yes, it will reverse polarity...this is also confusing me. It should act just like a regular motor. The "constant ground" is switchable via unlock relay. I can't figure this one out. the only way to actually get the latch to unlock is to bypass (i.e. short) the two micro input switches inside the exterior door latch to make the computer do it. When I tried to do it I disconnected the latch connector and applied power and ground with my power probe to the dk-g and tan wires on component side (when trying to eliminate the latch as a problem) but nothing happens.
The only thing I can think of is that maybe the motor has an electrical "latch" or "enable" system that the schematic is not showing. That is, perhaps there is another input to the latch motor that needs to be met to make the motor work. There is a "deadbolt" relay in the schematic that may play a role in this (i.e. see the Aux control BCM relay has logic inside). Something is missing in the schematic I suspect. I still have the car apart; any ideas as to what to try tomorrow?
Last edit: 7 years 5 months ago by ericblack. Reason: clarity

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7 years 5 months ago #2401 by ericblack
BTW, have you ever seen that synmbol before just before the motor? Maybe that is important too. Not sure.

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7 years 5 months ago #2402 by ScannerDanner

ericblack wrote: BTW, have you ever seen that synmbol before just before the motor? Maybe that is important too. Not sure.

Never saw one before but is absolutely key in understanding this circuit. That constant ground is for that logic circuit not the motor.

Don't be a parts changer!

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7 years 5 months ago #2406 by ericblack
Ok, I will do some research on this. I will let you know what I find. One more thing, I have compiled quite a lengthy linked list page to your "You Tube" free videos with a video description for each link (see link below). I did this for me, but any user on here can use it freely. Once again, thanks for your time. I have left you a book review btw. Awesome work, Paul.

link:
sites.google.com/site/ebautomotiveonline/external-links

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7 years 5 months ago #2433 by ericblack
I have an update on the Cadillac CTS 4 3.6L. I gave some misinformation earlier when I said that the motor in the latch was bidirectional....It has only one polarity to it. The way it works is this; when the door is shut, it ALWAYS locks. The act of shutting the door causes the latch to lock. When pulling the handle on the drivers front door the computer will then power the e-latch to unlock it. When the door is shut again, it locks (not electronically but mechanically). This, then, is the operation of the e-latch; however, I was still unable to energize the latch by giving it power and ground. Perhaps the only way to test this latch operation is to scope the pulse being sent to it and somehow mimic this "pulse". The car is now gone; however, if anyone could shed some light on the subject that would be much appreciated...thanks, Eric.

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7 years 5 months ago #2441 by Noah
I thought this was interesting:

Power Door Lock Deadlock Motors

Some vehicles may be equipped with the deadlock feature, which includes a reversible deadlock motor contained within each door latch assembly. Each deadlock motor is wired to the lock and unlock relays through 2 control circuits; the door lock actuator lock control circuit and the door lock actuator unlock control circuit. To deadlock a door, the door locks are activated by momentarily supplying voltage to the door lock actuator lock control circuits, and ground to the door lock actuator unlock control circuits. The voltage to the door lock actuators is provided through the normally open switch contacts of the theft deterrent alarm relay. To complete the deadlocking, the theft deterrent alarm momentarily energizes an internal relay causing the switch contacts to close applying voltage to the deadlock actuator control circuits for both front and rear doors. Ground to the deadlock actuators is provided through the door lock actuator unlock control circuits. Once the doors are deadlocked, the mechanical lock/unlock linkage within the door lock actuator is physically disconnected so that the door can not be opened even when manually unlocked. If the content theft feature is armed at the same time, the interior door lock switches will not operate the locks.

To undeadlock the doors, the BCM unlocks the doors by momentarily applying ground to the deadlock motor unlock control circuit. This energizes the rear door unlock relay coil causing voltage to flow through the switch contacts to the door lock and deadlock motors. Ground for both motors is supplied through the door lock motor lock circuit through the normally closed contacts of the lock relay to ground.

Driver Door Key Cylinder Switch


"Ground cannot be checked with a 10mm socket"

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7 years 5 months ago #2442 by Noah
I have a question that may sound stupid, but I think bears asking. When you were trying to activate the e-latch, was it with the door open? And with the latch open? I imagine you would need to close the latch with a screwdriver or something in order to make it release. I apologize if you mentioned this and I missed it.

What a roundabout way to open the doors. Good thing batteries never go dead overnight...

"Ground cannot be checked with a 10mm socket"

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7 years 5 months ago #2456 by ericblack
Noah, what i did was use a screw driver to lock the latch; however, even with the latch already open, you will still here the motor operate when pulling the handle. So, that wasn't an issue. Also, if the battery goes dead, the fob has a built in key that can be used to also open the door.....however, the customer wanted to unlock the door by just lifting up on the exterior door handle the way it was originally designed. I have yet to figure out why I couldn't apply a constant power and ground to make the latch work. By looking at the schematic, I should be able to do this. Guess we will have to wait until someone here figures this one out or gets one in their shop. As of right now, the only way to test the latch on these Cadillacs is to short out both micro switches in the exterior door handle......it took 4 bullet peircing probes to do this. Still practical, but still would like to know why I can't "be the computer" and make the latch open by electrically applying power and ground. But thanks for the replies, Noah. If I find out any further information on this I will post it here. Thanks, Eric.

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1 year 1 month ago #60012 by mwood1164
So does anybody have more info on this deadlock feature?

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