Inside trunk release doesnt work but fob does

Hello all,

I have a 1999 Pontiac Grand Prix GTP with a trunk release issue. I bought this car used, and when i bought it my key didn't work for the turnk. The only way for me to ever get into the trunk was either using the button in the glovebox or using the FOB.

Problem: The trunk release in the glovebox is now no longer working. I'm starting to get worried that I will be on a camping trip or something and I will get locked out of my trunk if my fob dies.

-I have checked all of the fuses and everything seems to be good there.
-My back up lights also are in working condition which I have come to learn can sometimes be related.
-I have ran a continuity test with the trunk release button and that seems to be fine.
-I tried checking the amps through the trunk release button and there does seem to be a small amount of amps running through(Maybe i should have checked volts instead?) so to my untrained eye it seems like the wiring connected to the button is ok?

I noticed last night then when i use the FOB I can hear a relay clicking near the stearing wheel so i thought i would investigate. Although I'm not really sure what I am doing/looking for, I took a bunch of the driver side dash(under the steering wheel) apart. I have located the relay for the trunk. It looks like there are two sets of two wires going to the relay. One of them I believe is +12V that runs to the trunk seleniod. The other set is for the switch in the relay.

I read somewhere that the trunk release is wired through the neutral safety switch(Which is a pain in the butt to get to in this car). Does anyone know if the FOB trunk release is also wired through the neutral safety switch? This may be unrelated, but about a year ago, there was a wiring issue in this car dealing with the shift release. My car would never shift out of park and it ended up being a break in a wire down by the shifter. Could this possible have anything to do with it?

Also, does anyone have any wiring diagrams that show how all of the connections are made between the trunk release button, the relay, the keyless remote module, power and the trunk seleniod?

Does anyone have any suggestions or thoughts for me?

Thanks everyone!

Steve

Doe's the hardware keyed trunk work?

Doe's the hardware keyed trunk work?

whats the "hardware keyed trunk"?

Can you open your trunk with key, not FOB?

No, i bought the car used and the key has never worked for the trunk. Currently, the FOB is my only access to the trunk. That is why i really want to get this trunk button working in the glove box for a back up.

The signal wire for the truck release might be fused, did you check for any fuses?

-I have checked all of the fuses and everything seems to be good there.
-My back up lights also are in working condition which I have come to learn can sometimes be related.
-I have ran a continuity test with the trunk release button and that seems to be fine.
-I tried checking the amps through the trunk release button and there does seem to be a small amount of amps running through(Maybe i should have checked volts instead?) so to my untrained eye it seems like the wiring connected to the button is ok?


As stated above, I have checked the fuses. I have read that if it was a fuse problem the rear back up lights would also not work. My rear lights are working though so i assume its not a fuse problem.

From my understanding, the fuse would only be for the 12V running to the trunk. I'm thinking there wouldn't be a fuse just for the push button.

Would there be an inline fuse or something not at the fuse box for the push button? Seems like a fuse for a push button would be overkill and not needed.

As stated above, I have checked the fuses. I have read that if it was a fuse problem the rear back up lights would also not work. My rear lights are working though so i assume its not a fuse problem.

From my understanding, the fuse would only be for the 12V running to the trunk. I'm thinking there wouldn't be a fuse just for the push button.

Would there be an inline fuse or something not at the fuse box for the push button? Seems like a fuse for a push button would be overkill and not needed.

My first instinct would be bad button in the glove box. Try shorting around it with a solid clip lead.

You need to verify that there is 12v on the green wire (terminal b) at the release switch. Yes the switch is wires through the "transaxle range switch" and will not open in any position other than park, so there may be an issue with the switch. If the trunk opens with the fob, then the actuator and MOST of the ground ckt is verified as ok. If you check resistance from the switch to the actuator it should be less than 1 ohm. So check for power at the switch if there is 12v and the ground side is good, then the switch is bad.

As stated above, I have checked the fuses. I have read that if it was a fuse problem the rear back up lights would also not work. My rear lights are working though so i assume its not a fuse problem.

From my understanding, the fuse would only be for the 12V running to the trunk. I'm thinking there wouldn't be a fuse just for the push button.

Would there be an inline fuse or something not at the fuse box for the push button? Seems like a fuse for a push button would be overkill and not needed.

My first instinct would be bad button in the glove box. Try shorting around it with a solid clip lead.

My first instinct would be bad button in the glove box. Try shorting around it with a solid clip lead.

Tried this, also tested the continuity of the button with a multimeter and everything is good there.

You need to verify that there is 12v on the green wire (terminal b) at the release switch. Yes the switch is wires through the "transaxle range switch" and will not open in any position other than park, so there may be an issue with the switch. If the trunk opens with the fob, then the actuator and MOST of the ground ckt is verified as ok. If you check resistance from the switch to the actuator it should be less than 1 ohm. So check for power at the switch if there is 12v and the ground side is good, then the switch is bad.

Hey gmtech. I assume all of the "switch's" you are referring to that I underlined above you are talking about the pushbutton in the glove box? If so, I am concluding from what you have said that the button is the glove box does not run through the trunk release relay on the driver side then? Is that true? Is that relay only used for the FOB?

How do i verify that there is 12v at the release switch? If your talking about the glove box switch, do i just set a multimeter to volts and prob both ends of the wire harness that the switch usually connects to?

To check the resistence from the switch to the actuator, how do i know which of the two terminals from the switch to use? After I pick the correct terminal, do i just prob that terminal and then connect a long wire to the last prob and then run that wire to the wire running to the actuator? Do i have to unplug the battery for this? I'm guessing no since the wire shouldn't be live?

Hey gmtech. I assume all of the "switch's" you are referring to that I underlined above you are talking about the pushbutton in the glove box? If so, I am concluding from what you have said that the button is the glove box does not run through the trunk release relay on the driver side then? Is that true? Is that relay only used for the FOB?

How do i verify that there is 12v at the release switch? If your talking about the glove box switch, do i just set a multimeter to volts and prob both ends of the wire harness that the switch usually connects to?

To check the resistence from the switch to the actuator, how do i know which of the two terminals from the switch to use? After I pick the correct terminal, do i just prob that terminal and then connect a long wire to the last prob and then run that wire to the wire running to the actuator? Do i have to unplug the battery for this? I'm guessing no since the wire shouldn't be live?

Yes, the switch that I am refering to is the glove box switch. The green wire should have 12v when the shifter is in park. Set the meter to DC volts and connect the red lead to the green wire, then the other one to a good ground. If you have 12v connect the test leads to both terminals in the connector. If there is 12v then power and grounds are good. If there is not, then there is a problem between the blk/wht wire from the connector to harness connector (c200) under the dash, or in that connector itself, Its a big square connector with 56pins.

From what I see, the relay is only for the key fob.

to check resistance, probe the blk/wht wire from the switch to the actuator

Thanks everyone for all your help and your speedy replies!

How about buying a spare FOB from Ebay, and duck tape it to the dash!

You need to verify that there is 12v on the green wire (terminal b) at the release switch.
Looks like I am getting ~.5V to the green wire. I also just noticed the the car is a 1998 not a 1999. I'm not sure if that changes how much volts it should be getting.

What would be my next step if its only getting .5V to the button? Also, can someone please verify that the fuse I should be checking is fuse 27 under the hood? It is listed as the "Back Up light" fuse, but I read somewhere this was the one I needed to check. I dont see any "trunk fuse".

When in doubt, roll the fuse with another the same type.
It took me a couple of days just to find a hidden Relay/resister for my DRL.

Yes, Back Up Lamp fuse (10amp) fuse is the correct one. '98 and '99 are the same. You should have 12v. Check the light green wire and connector C1 at the transmission select switch, it's the 7pin connector, termiinal C, leave it lugged in and back probe it, it should have 12v. If not, check the orange wire, same connector, terminal B. This one is the power wire to the switch from the fuse. It should have 12v. If the green wire has less than 12v, the trans switch is bad. If there is 12v on the green wire and only 5v at the release switch, then there is a problem between the release switch and the trans switch. If the orange wire has less than 12v there is a problem between the fuse box and the switch.

Why not, open the trunk with the key fob, then pop out the lock cylinder and replace it?

Or, if you have the "pass though" rear seat(arm rest folds down and there is a locked panel that allows you access to the trunk), keep a long screw driver handy that you can use to unlock the trunk through the opening......

Why not, open the trunk with the key fob, then pop out the lock cylinder and replace it?

Or, if you have the "pass though" rear seat(arm rest folds down and there is a locked panel that allows you access to the trunk), keep a long screw driver handy that you can use to unlock the trunk through the opening......

Replacing the lock cylinder is not a bad idea. Any idea if that would be expensive/hard? I also just think the idea of something not working gets me worked up.... I sort of just want to fix it ya no :)

I do have the "Pass through". In fact I have praticed unlocking the trunk that way in case I need to. :) My worries however are that I will have my bike or large boxes or something that i would not be able to get out through the "pass through" and would be in my way of opening the trunk.

Check the light green wire and connector C1 at the transmission select switch, it's the 7pin connector, termiinal C, leave it lugged in and back probe it, it should have 12v.
The green wire (terminal c) on the Neutral safety switch(NSS) has 12V's.

Does terminal c run directly to the switch? I'm hoping there is another(easy to access :uhoh:) terminal inbetween the switch and the NSS. Any more advice? I'm hoping the next step isnt rip apart the entire dash. :disappoin

12volts->Switch->Fuse->load (trunk latch)->GND

We already know the FOB & trunk latch works!
Suspect a bad fuse, switch, or path to ground.

What keeps the trunk switch from trigger while the auto is in motion?
NSS

Replacing the lock cylinder is a good idea, no,its not that difficult.

Here is where your wiring problem get interesting. That green wire runs back to the underhood junction block (fuse box with the back up lamp fuse in it) then passes though it and out, then goes straight to the trunk release button. The connectors in/under the fuse box and big with LOTS of wires. You may try just unplugging them and then reattatching them. They ususllay have a bolt in the center of them holding them to the fuse box. Also, look for rodent damage under there. It would be next to impossible for me to describe excatly which terminal to look at, but the wire stays the same color.

12volts->Switch->Fuse->load (trunk latch)->GND

gmtech is leading me to believe it's more like:

12V -> NSS -> Fuse -> Switch -> Latch -> GND

At least as far as I gather.

Well, I checked the back of the fuse box. The wires actually looked to be in pretty good condition. One of the fule pump relay wires was the only one I could see damaged.

After looking at fuse 27(trunk/backup light) which was orange I am rather confused. I assumed that for every two socketed fuse, there should be two wires connected to it. Fuse 27 only had one wire going to it. This completely destorys any of my understanding of electronics unless the other end of the fuse is connected to the battery within the fuse box?

Gmtech, I'm a little confused. Does the orange wire carry +12V from the fuse box to the NSS and then the green wire takes the 12V and send that to the switch which then in turn brings it to the latch? Thats how you made it sound before. If that is true, and the green wire on the NSS had 12V, wouldn't that mean there is some sort of a short between the NSS and the trunk release switch? Furthermore, I wouldn't need to look in the fuse box correct?

Other than looking for obvious damage to wires leading to the fuse box, is there any messurements I can take in the back of the fuse box to eliminate/conclude anything? I'm not really sure where else to go with the fuse box.

| Document ID: 516245
Release Systems Schema


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Thanks for the diagram!!!! Exactly what I was looking for. Where does someone go about getting diagrams like this?

Through deductive logic, it looks like my issue has to be somewhere in-between terminal C2 at the junction box and terminal B at the switch. Since C4 and C2 are joined at the junction box, and C4 is used for the trunk relay fob, I think it’s a pretty safe assumption that C2 is also getting the correct voltage, althought I will still try to find this terminal at the junction box. gmtech, do you know what “p100” in-between the junction box and the switch is? Is it a wire harness? If so, do you have any clue where that would be located?

The diagram is from a GM service manual. The "P" in P100 indicates a "pass thru", this is where the harness "passes thru" from the engine compartment to the passanger compartment. There is no connection there.

1) Isolate LT GRN wire from point B on the connector on rear compartment Lid Release Switch , by a disconnect.
2) Barrow hot 12vdc from anywhere & connect it to point B switch.
3) Push rear trunk release switch.

Caution - Don't push rear trunk release while vehicle in motion.

TRS signal is lost (P100), this is the battery for the rear compartment Lid Release Switch, try running a new wire from point C4 to trunk switch.

The problem is between the junction box an the switch. Good news is that its only a wire that needs to be replaced/repaired. Bad news is that I may need to rip the dash apart. Anyone know of any common spots between then junction/fuse box and the switch that a wire might become defective?

Any advice for finding a bad spot along a wire? I was thinking I could maybe cut the wire somewhere in the middle, then I could test for continuity on both ends and at least figure out what end the break is happening. Divide and conquer ya know. Or is this a dumb idea? Any suggestions? Like I said before, I feel like I am going to have to rip apart the dash. :banghead:

And yes, I know there are work arounds for this, but I really want to fix it. My car is in 100 peices and I am 95% of the way there.
:gives: ME! :ylsuper:

Just tywrap a new wire to the buss line and be done!

How do i get the new wire through the fire wall? There seems to be a rubber boot of sorts around the wires being passed on both sides of the fire wall. Do I have to remove that rubber boot? I tried to take it off but I had no room to mess with it and it was rather stuborn.

That would be P100 that you were asking about. Go from the inside of the car and push a piece of mechanics wire through the rubber grommet, wrap the new wire around the mechanics wire and pull it through to the inside of the car.

Do i need to take that rubber "boot" thing off first?

I finally got the car all put back together yesterday. Everything is up and running now and the trunk button works! Thanks everyone for all of your input! Couldn't have done it without you!

For anyone that reads this in the furture:
I was able to run the wire through the firewall through the same hole on the passenger side of the car were the rest of the wires pass through. If, from the inside of the car, you pull a little bit on the wires that are passing through the firewall, a little foam pad that surrounds the wires will become loose. Once loose, I removed that foam pad. I then took a coat hanger, straitened the hanger and then bent it in half. I then pushed the bent end of the hanger through the firewall right along with the rest of the bunch of wires. I pushed the wire all the way through the rubber boot on the engine compartment side of the car. Once pushed through, I ran the electrical wire through the coat hanger just like threading a needle. After that I pulled the hanger back into the inside of the car and bam, the wire was ran through the fire wall. I then soldered both ends, wrapped the wire with electrical tape and I was finished.

Hope this helps some people in the future!

Thanks again everyone! :bigthumb: