I'm having the trunk release issue on my 2018 LT, the trunk release seems to be grounding out somewhere and releasing the trunk randomly. After a couple weeks, the trunk release buttons won't work either. I've replaced all the switches, harnesses and latch in the trunk lid. The lights flash when I use the remote, but it doesn't open. The fuse is good. Does anyone know how to test the built-in relay using the test point(#24) on the under hood fuse panel? Any help would be awesome...
HdeVille
Welcome to the forum. Are you saying the relay for the trunk release is built into the under hood fuse panel rather than a removable relay? Do you have any pictures of the relay in question and of test point 24 as this may help others try and help you.
Do not have access to a 2018 wiring diagram but I do for a 2017 and it shows that there is a Blue/ yellow wire that supplies power (12Volt +) from the relay to the trunk release solenoid when the relay contacts are closed. This should activate the trunk release which is connected to a ground point in the luggage compartment. I assume that 2017 and 2018 would be similar but I may be wrong and they may use different coloured wires between 2017 and 2018. Looks like the relay primary coil is supplied 12 volts (grey yellow wire) when the BCM receives a request to release the trunk from the dash switch or from the remote. Looks like the relay contact that supplies power when the relay is powered on is connected to ground when it is not powered on - possibly for the trunk ajar signal but not sure. Hope this helps and makes sense.
Do not have access to a 2018 wiring diagram but I do for a 2017 and it shows that there is a Blue/ yellow wire that supplies power (12Volt +) from the relay to the trunk release solenoid when the relay contacts are closed. This should activate the trunk release which is connected to a ground point in the luggage compartment. I assume that 2017 and 2018 would be similar but I may be wrong and they may use different coloured wires between 2017 and 2018. Looks like the relay primary coil is supplied 12 volts (grey yellow wire) when the BCM receives a request to release the trunk from the dash switch or from the remote. Looks like the relay contact that supplies power when the relay is powered on is connected to ground when it is not powered on - possibly for the trunk ajar signal but not sure. Hope this helps and makes sense.
Yes, the fuse is built in, when I 12V test the test point to a ground it reads 0.2 volts(I don't know what this means or what it should read...) I also have the wiring diagram from the Factory Repair Manual that I bought on EBay. I know the colors of the wires but can't access any of them without tearing apart the harnesses or fuse panel under hood....
Can you post a picture of the wiring diagram that shows the relay, the test point and the trunk release?
Edit: Attached is a picture of a 2017 Trunk Release Circuit - I assume your 2018 will look similar. Made some notations on it to give you an idea of how it works - hope this helps you.
![Image]()
Edit: Attached is a picture of a 2017 Trunk Release Circuit - I assume your 2018 will look similar. Made some notations on it to give you an idea of how it works - hope this helps you.
I also replaced every part and harness in the trunk lid and can not get it working. Do you have any issues with the parking lights on the trunk lid? Does yours pop the trunk when the lights turn on???
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