Trunk Inoperative Using Trunk Button

[ald42]

love this forum

You are correct, the sensors are potentiometers. There are three. You've already found one on the driver's side scissor lift for the rear deck lid. That is the rear tonneau position sensor.

The front tonneau position sensor is visible from the rear of the car (with the rear deck lid raised) and is located on the forward wall of the trunk between the seats on the front tonneau mechanism. Earlier model XLRs have a fabric cover over the front wall which may obscure your view of this sensor.



The final sensor is located on the inside of the cabin on the left side of the roof adjacent to the speaker on the left side of the seat behind the roof's vinyl cover. This is the top position sensor.

The mechanism that locks the roof in place (it basically clamps the front of the roof to the windshield header) has an open and closed switch. You have to remove the headliner to view it. There's another switch on the passenger side of the windshield header that is activated when the top's locating pin goes into its receptacle.

The self-clinching latch on the rear of the trunk also reports its status to the folding top control module.

The switches are fairly reliable. The sensors are less reliable and account for the majority of the failures associated with the folding top. They either change tolerance over time, or become mechanically loose, (there's only one locating pin instead of a more reliable two) so the sensors are able to rotate around the single pin. After enough failures had been logged, a technical bulletin was issued to address this issue and position sensors were (supposd to be) epoxied in place during subsequent replacement. A more robust design would have used optical position sensors, but it is what it is.


Hope this helps a little.

CC

this helps a lot!! another one of my 78 reasons why this is the best forum. a BIG THANK YOU,cc

 

[ccclarke]

The position sensor located on the driver's rear deck lid side scissors lift mechanism is for the rear tonneau (the panel that retracts under the rear decklid.) Knowing this, take a look at it again and you'll see how it all comes together.

The front tonneau consists of the three flaps that move after the windows lower. Like a lot of XLR-related things, they can go by two different names: Front and rear close-out panels.


I wrote an extensive post a few years ago describing the workings of the folding top in great detail. A quick review might be of some help to you. Give the Search function a try. If you can't locate it, I'll start digging.

As our cars reach the ten-year mark, (some 2004's were built in 2003) the folding top in particular may start to exhibit issues when retracting or stowing. Knowing how the top sequence operates can help you determine if you need professional (ie: dealership) help.

For example, if the rear decklid won't raise when trying to stow the top, the front tonneau position sensor may be to blame. Why? Because after the windows lower, the next step in the sequence is the raising of the front tonneau. It might fully raise, but if the stored values don't match the measured values, the folding top control module will stop the process. The rear decklid (being the next mechanism to move in the sequence) will just sit there, daring you to throw money at it.

By knowing what is supposed to happen, you can zero in on what might be causing the problem. In this case, the rear deck lid may still operate from the dedicated raise switches, (on the lower dash and above the license plate) since they aren't part of the normal folding top raise/retract process.


That being said, if the front tonneau position sensor is flaky, it can also exhibit the opposite symptoms: The folding top will retract/raise (with some obstinate hesitation) but the local control switches for the rear decklid will become useless, and pressing the switch over the license will unlock the latch and allow you to lift the rear deck lid (with lots of difficulty) by hand. I know these two paragraphs sound contradictory, but one bad sensor can give two different symptoms and I want to include as much information as possible before the effects of this evening's three beers set in and I start describing the inner workings of the F-150's suspension.

The folding top position sensor opration is pretty straight-forward, as is the rear tonneau's. If they're bad, the mechanism they control probably won't work properly. The switches are easy to diagnose. And easier if you can get your lucky hands on a Tech-2. As the switches trip, (or don't) the status is displayed in glorious blue and white.


BusaMan: You asked how the folding top control module knows when the rear deck lid is lowered. There is a latch with a built-in switch that captures the "hook" on the rear deck lid. The hook pushes the latch over it to pull and lock the rear deck lid down and activates a switch in the process. The switch position signal is sent to the ftc module.

--Hope this gives you some helpful insight into the folding top's operation!

CC

 

[BusaMan]

Nailed It!!!

CC, you're awsome.

I took it into the dealership (Red Noland, COS) and armed w/ your explanations, I suggested they check out the sensors and see if reinitializing/resetting the Top Control Module would fix the problem. One hour of labor (about $100) and it was all fixed. The tech updated the TCM "software" and it's all working as designed. Even a little better than when I bought the car, due to reduced hesitation when closing the trunk lid.

When our hectic lives settle down a little, after the forthcoming election to recall our POS state senator, I think I WILL go find your discussion of the principles of operation of our arcane top system. I honestly am amazed every time the darn thing works.


CC, I sincerely appreciate your taking the time to explain in some detail how this feature operates. We all gain knowledge when we make the effort to share and I thank you for making this complicated system a little more understandable.

If ever I am able to swing making one of the forum trips (I AM going to make the Rod Rocket Rendezvous [R[SUP]3[/SUP]] next summer in MT), I'll buy you a beer (or 3).

Tim

 

[ccclarke]

That's great news Tim! I'm glad the dealer was able to get your top in tip-top shape!! (No pun intended!!)

As for out-West XLR rendezvouses, I won't be in a position to make those for awhile. I just moved from CA to CT this week and had my XLR shipped out via covered transporter, which arrived today. Looks like it won't be a daily driver anymore and I'll become one of those poor souls who store them for months on end.

So now I need to find an AWD Cadillac to get me through the long New England winters!!!

Any suggestions?!!

CC

 

[BusaMan]

CC, you could always move back, whaddyathink???

That's great news Tim! I'm glad the dealer was able to get your top in tip-top shape!! (No pun intended!!)

As for out-West XLR rendezvouses, I won't be in a position to make those for awhile. I just moved from CA to CT this week and had my XLR shipped out via covered transporter, which arrived today. Looks like it won't be a daily driver anymore and I'll become one of those poor souls who store them for months on end.

So now I need to find an AWD Cadillac to get me through the long New England winters!!!

Any suggestions?!!

CC

 

[Shydiggy44]

It seems the part numbers listed are nowhere to be found for the sensors? I am having the exact same problem as the gentlemen before and no place can find them or repair this. I have checked the GMparts online and ordered but only to be cancelled and money returned stating no long available. Is there a substitute part maybe from the convertible corvettes that could be used?

 

[IAN]

shydiggy44

On the above of this page, there is an AD from Top Hydraulic, click on his address and look for its Video.

There is 10 video made by this repair shop of retractable top of all makes, the number 8 video he is explaining on how to handle the sensors and the top switches.

That will get you famillar with the system, he is also giving tips on how to solve some of the sensors/switches.

You can call him for additional informations and perhaps the parts available or where to get them.

Good Luck

IAN