451 Boot Switch Faults

The 451 boot release switch is problematic and will slowly become a common problem. These issues come in 3 forms.

1 – Broken Mechanism
2 – Faulty Switch
3 – Damaged Wiring

1 – Broken Mechanism

The actual switch is fine and well hidden. For the number of times you open the boot, the switch should last the lifetime of the car. The problem is the lever that actuates the switch. As you can see below, the feather of the switch rests against a plastic tab…

…and when the handle is pulled, the plastic tab lifts and activates the switch.

The tab passes through the main housing to the handle. The problem is that the tab is fairly thin so is more prone to break as the plastic ages and the longer it has to live with you pulling on it like a 400lb gorilla.

Here you can see the end of the tab has broken off…

…so the handle no longer pushes the switch. No pushy, no openy. Depending on where it snaps, the handle can jam in the lifted position.

Step 1

Firstly we need to remove the handle. Push in the pivot…

…so you can lift the handle out of the housing.

This is what is left of the housing with the handle removed.

Fix 1

This wasn’t my idea but it’s my preferred fix. Get yourself a momentary button (sometimes called a push-to-make switch), ideally one that’s water resistant. Drill a hole, fit the switch and, cut the wires from the existing switch and connect the existing wiring connector to the new switch. It doesn’t matter which way around you wire it.

Fix 2

I bought a 3D printed replacement from Shapeways, link was here. Unfortunately he doesn’t seem to be selling them any more.

It’s a very simple design so you can design your own or I’ll design one at some point and will post it here.

Fix 3

Go to a smart dealer and order part A451 747 01 87.
You can also look on eBay for 2nd hand ones but they may not last long and may be more expensive than a new replacement.

2 – Faulty Switch

The actual electrical switch is unlikely to fail but it’s not impossible.

If you lever the metal retention plate off that holds the switch in place, you will damage it beyond repair. Check the switch with a multimeter to be 100% sure it’s the fault. Cut the switch to pieces so you can remove the metal retention plate with the plastic tabs still in it. That way you can push the plastic pegs through the retention plate and reuse it.

I don’t have any part numbers for a replacement switch. If you work it out, let me know. You will probably have to cut the existing wiring connector off the old switch to connect it to the replacement.

If you can’t find a replacement microswitch, you could just replace it with a push-to-make momentary switch like this.

3 – Damaged Wiring

This is a new one but I’m not surprised it became a fault. Sebastian S let me know that his boot switch stopped working however, when he tested the physical switch, it was fine.

Using a multimeter he checked the continuity of the cables. He found that the earth cable had snapped. It runs from inside the boot of the car and through the rubber grommet (bellows) to the switch.

He repaired the cable and it began to function correctly. I would recommend pulling a new cable through and replacing the failed cable.

How To Remove The Boot Switch

Have a look here.