Yeah, if it pops open with the remote, the relay and fuse are okay. What kind of shape is the vehicle in and how many miles? Have you had front door or accident repairs done? I ask because a well-used car could have severed copper filaments in the wiring harness at the front door and/or the trunk lid.

In fact, severed wires in the harness inside the trunk lid liner are pretty common with this model - that may or may not be your issue but I would start there. Remove the trunk liner (it's held on with fasteners that easily pry off). The next step is to remove the wiring harness sleeve and then examine each wire for breaks. When I had issues, I found three or four wires were at various stages of breaking.

Again, that harness may not be your issue but I'd start there.

Welcome to the forum @Mike55

 

The car is in great shape. I purchased it used.carfax said no accident. It has 50k miles.

the button worked for 3 years. It was intermittent for a couple of months. Now it is dead. I keep thinking it is a rusted button.

 

if I had a wire issue, why would it work with the FOB?

have you ever pulled the door button? Do I have to take the entire panel off?

thanks

 

Do you hear the relay when you press the button on the door?

Your fob works because the receiver sends a signal on a different wire than the button does because the receive and door button are not located in the same place.

You should examine wires first. They break.

You haven't answered my other questions.

 

Does the trunk open from the pad, on the trunk lid?

 

Not all CTS' were equipped with the touchpad on the deck lid.

 

Attached is the schematic. If the fob works then the relay is good and the pad on the trunk lid itself should also work. I say this because the pad on the trunk sends its switch input to the RCDLR (remote control door lock receiver) which sends a low speed buss message to the BCM to request trunk relay operation.
If your door locks and all windows work then the communication from the door to the BCM is OK. The drivers window switch module sends messages to the other doors and the BCM to lock/unlock doors and to open/close the other windows. If you can control the other windows that leaves just the button itself or a connection from the button to the window switch (in the drivers door as well) as the problem.

 

The membrane pad degrades from water intrusion and the wiring breaks. You likely need both. And the trunk can leak water, if you have that problem.

3rd brake light problem

I joined up today for help with a couple problems and the first one is the 3rd brake light. I just bought a 2009 CTS and the third brake light is not working, tail lights are. I checked the fuse in the trunk and it is fine. I took a 12v tester and checked the plug for the light and got no...

www.cadillacforums.com

 

My deck lid "pad" has been inop for years, but everything else works.
For the few times I enter my trunk, the juice is not worth the squeeze.

 

My trunk light is out, surely a broken wire again. Haven't fixed it yet.

 

Bad button or connections from the button to the window switch module.
Remove door panel and test button with ohm meter. Unless the button is outrageously priced I would buy one so it is ready to install when you have the door apart.

 

The trunk opens with everything but the button. The trunk release relay is under the rear seat. If a wire is broken in the trunk hinge harness the trunk wouldn't open.
The windows all work so the low speed buss wire in the drivers door harness - the one that also carries the trunk release message - is not broken. The BCM can operate the relay to open the trunk because that is how all the other system activate the relay so that wire is not broken. The only possible broken wire is the one between the button and the drivers window switch module inside the door. It is either that or the button itself. I vote for the button.

 

If a wire is broken in the trunk hinge harness the trunk wouldn't open.

It's not that simple, one method can work while another doesn't due to broken wires. It happened on my car and has been observed by others on the forum.

 

Yes Lifespeed I agree. There are wires that can break that will disable some functions but not others. I made my statements according to his failure on his car using the schematic. In this instance, and i showed my work, there is really only 2 likely failures. The button or the wires to the button. Full disclosure, there is a very unlikely 3rd possible failure that I just thought of. It would be possible for the input of the drivers door module that reads the trunk release button to fail. Not very likely but possible. I may have missed something else in the schematic that you know of or have experienced but I don't think so.
Anyway, I have no problem being proven wrong so if you want to tell me specifically where I made my mistake then go ahead.
Really, no meanness or ill will intended, I'm all for learning when I screw up!

 

Your button is bad. Replace it. Mine did the same, intermittently wouldn't work, then stopped all together. New button, good as new.

 

I agree but How did you replace the button? Does it just pop off. It could also be the contacts in the button similar to what happens in the door release button. I’ve cleaned the contacts several times since I’ve owned with no issues.