Trunk release not working - WN 2014+

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vetterss
Posts: 52
Joined: Mon Dec 03, 2018 3:46 pm

Trunk release not working - WN 2014+

Post by vetterss »

2015 Caprice still struggling with trunk release buttons. With car on, neither button works and the key fob doesn't work either. The fuse in back looks good. When pushing the fob can hear a clicking somewhere near the back seat in the trunk but not sure why that is. Does anyone have a trunk wiring diagram or other suggestions on how this may have been bypassed?
Mike
1973 Corvette Coupe
2023 C8 Corvette Coupe
smwalker
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Re: Trunk release not working

Post by smwalker »

So here is the electrical release diagram. Looks like circuit 1303 is the actual release circuit to the latch. Circuit 6188 seems to be the one that only energizes the circuit if the vehicle ignition is on. SO you got an extra relay there (KR95B) that could be bad. Side note you could do a bypass at this relay and make your trunk release work from inside the car with the key off. MIght have to do a write up on that little trick.

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LUGGAGE COMPARTMENT DESCRIPTION AND OPERATION (VEHICLE ACCESS)


Rear Compartment Lid Release System Components:
Body control module (BCM)
Rear compartment lid unlatch switch-driver
Rear compartment lid unlatch switch-passenger
Rear compartment lid latch
Rear body fuse block (contains PCB relay)


Rear Compartment Lid Release Operation
Interior Rear Compartment Lid Release Switches
The BCM monitors a voltage signal to the interior rear compartment lid release switches so that when the switch is pressed, the voltage within the signal circuit is pulled low and in response, the BCM will detect the voltage drop and will provide voltage to the rear compartment lid unlatch PCB relay.

Rear Compartment Lid Latch
When BCM receives a rear compartment lid release command from a rear compartment lid unlatch switch, the BCM applies brief pulse of voltage to the rear compartment lid unlatch PCB relay control circuit, which energizes the coil side of the relay. The switch side of the rear compartment lid unlatch PCB relay then momentarily closes, supplying a brief pulse of battery positive voltage to the rear compartment lid latch. The rear compartment lid latch is continuously grounded and when it receives the voltage pulse, it will become energized and the latch will activate releasing the trunk lid so that the trunk lid may be manually raised to an open position.

Keyless Entry Transmitter
The BCM may also get a rear compartment lid release command from the remote keyless entry module. When the trunk button is pressed on the keyless entry transmitter, a rear compartment lid release request is sent to the remote keyless entry module, the remote keyless entry module will then send a serial data message to the BCM to command the release of the rear compartment lid.

Trunk Open Message
The body control module monitors the voltage level of the trunk ajar signal circuit which is normally at the system voltage when the trunk lid is closed. When the trunk lid is ajar or open, a switch within the latch assembly closes providing a path to ground for the trunk ajar signal circuit. The voltage within the signal circuit will then drop to 0 volts, the body control module will then detect the voltage drop and will send a serial data message to the instrument cluster. The instrument cluster will then display the Trunk Open message.
Steve Walker
Azusa, CA
'11 PPV 9C3 Huron White
smwalker
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Re: Trunk release not working

Post by smwalker »

So here is a kink. Further researching the trunk lid relay I have found it is not serviceable??? Meaning it is integrated into the fuse box board (Fuse block in the trunk). That is very interesting in that an entire fuse box may need replacing if the relay goes bad? Not good. I have a 14 fuse box I will have to get some pictures of it to confirm. But note the red writing in the fuse box listing:

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So here is the Entire Rear Compartment Fuse box listing. Will want to check Fuse F128 to make sure you are sending battery power to the relay. If the relay is internal cannot test it like switching it with a known good one. Would just want to check at the latch connector with the key on to make sure you got battery power at Terminal 3 with the blue and white wire. If no battery power is present I would think you either got a bad relay integral to the fuse box or a break in the wire from the fuse box to the latch.

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Steve Walker
Azusa, CA
'11 PPV 9C3 Huron White
smwalker
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Re: Trunk release not working

Post by smwalker »

Sure enough the 14+ trunk fuse box has hidden relay's in there. Not sure if this is OP's problem but interesting none the less. Wonder why they did that? Non serviceable relay that's nuts.

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Steve Walker
Azusa, CA
'11 PPV 9C3 Huron White
vetterss
Posts: 52
Joined: Mon Dec 03, 2018 3:46 pm

Re: Trunk release not working

Post by vetterss »

You are a wealth of information and have definitely got me going in the right direction. The owners manual does reference the PCB but didn't realize that meant circuit board. I believe I have power at the actuator so it may be time to replace that.
Mike
1973 Corvette Coupe
2023 C8 Corvette Coupe
smwalker
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Re: Trunk release not working

Post by smwalker »

You know looking closer I do not think you will have continuous power at the latch on terminal 3. I think that will be momentary when pressing the release. I think the circuit 1303 is not the release but the monitor circuit . Open position the latch gives it a ground and tells bcm the trunk is open so the dash warning light comes on.

EDIT: Yes confirmed circuit 1303 is the ajar circuit not the activation circuit as I previously surmised. In this alldata wiring diagram they detail it out a bit more. The "Exterior Lights" is actually the red and blue emergency lights inside the trunk lid that come in some cars. 1303 provides a ground for them when the trunk is open.
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Steve Walker
Azusa, CA
'11 PPV 9C3 Huron White
vetterss
Posts: 52
Joined: Mon Dec 03, 2018 3:46 pm

Re: Trunk release not working

Post by vetterss »

Just a continuation note. My brother in law is an electrical engineer and we spent some time looking at the situation. He too believes the relays are weak and failing. Even though the manuals say the part is not serviceable, we will be removing the fuse box and replacing those relays. I bought exact replacement ones and in the next month or two when I feel brave enough, we will remove the fuse box and replace those relays. Will let the forum know if that fixes the problem or not.
Mike
1973 Corvette Coupe
2023 C8 Corvette Coupe
The_Real_Shrek
Posts: 3
Joined: Sun Sep 15, 2019 11:13 pm

Re: Trunk release not working

Post by The_Real_Shrek »

Has there been an update to this? I am having the exact same issue.
2822MM
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Re: Trunk release not working - WN 2014+

Post by 2822MM »

I had same problem on my 2014 PPV and found out the problem. The trunk actuator itself is the culprit. That sound you hear is the actuator trying to open “ an already opened trunk” since it does not recognize that it’s already opened position. If you get a screwdriver or something and manually push on the actuator towards down, you’ll see that it is now closed. Once that happens you can try to open the trunk while it’s open to see that it “NOW” opens with the interior releases or your key fob. The end solution is the actuator that needs to be replaced.
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