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      09-18-2017, 11:45 AM   #1
Jackal
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Drives: 2006 Z4MC (Bianca)
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Fixing a Trunk Latch that's not catching

I have had this issue a couple times in my year of ownership and the first time it just mysteriously fixed itself. This second time I couldn't get it to latch and hold the rear lid down, so it resulted in this DIY. I will add pictures if it ever happens again as I missed taking any this time. I hope that my description will suffice for now.

Firstly the symptoms. Very simply, when you close the trunk (hatch in my case), it will not catch and the door open light will not go out. Many attempts with the keys both manually and remotely did not correct it. Manually I tried locking the latch with a screwdriver and diagnosed that the latch itself was not catching, and it was not an issue of obstruction or the catch pin (in the trunk) moving.

The fix. Remove the latch from where it sits. This involves removing the interior panel surrounding the latch and loosening the two side panels the join up with the first panel. Then using three torx drivers, remove the latch and disconnect the two power leads from it. I also disconnected the emergency pull handle.

Opening the latch itself involved a few clips and a couple brass rivets. Unfortunately the only way I found to undo the rivets was to pull the lid off with a bit of force to pull the brass rivets through the plastic cover, effectively breaking the lid, but only slightly (still functions, and hardly noticeable).

Inside the latch is a motor with a screw gear that rotates a larger spur gear. That spur gear has a pin on it that resembles the pin needed for a coupling rod on a steam locomotive wheel. This pin presses on an arm in two points. When pressing on the top part of the arm it allows for normal latching, and when it presses on the middle hook part of the arm, it holds the latch open. Somehow the motor was interrupted and left the pin holding the latch arm open.

The spur gear is held in place by the lid that was removed, so its an easy fix to just wiggle it out a bit (past the worm gear on the motor), and rotate it. I tested this repeatedly with the electrics hooked back up, just to be sure I found the right placement of the spur in relation to where the pin needed to be.

Reassemble everything and you've fixed the challenge.
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