BMW M328i, Brake Light Switch Replacement

Well this is a familiar job, the old brake light switch failure.

A few drives ago I noticed the familiar “BRAKE LIGHT CIRCUIT” warning on the Check Control. Initially it was just a random warning that would pop up occasionally, but when checked, the rear lights still worked.

Unfortunately this escalated quickly, to the point where when I drove the car to and from work the other weekend, the warning would come up straight away, and sure enough, no brake lights were lit when the pedal was pressed. Eek. Back to the rear fog light when braking trick.

I touched on this error on my first E36, where I had the same issue. I replaced the switch a few times on that car due to faulty new parts, but eventually I got a good switch and the warning went away.

Replacement is fairly easy, once you know how the retention system works. If you try to fight the retaining clips, you will just make it much harder to get out.

This is the switch, in it “ready” state as it would be when installed in the car. The red collar is pressed into the body, and the plunger is short

To release the switch retaining clips, you need to extend that red collar by pulling it away from the body. There is one catch though, the plunger will not allow you to pull the collar out far enough, if the switch has been fitted, as the plunger doesn’t extend out far enough. The plunger is on a ratcheting system, and needs to be forcefully pulled away from the body.

With the plunger extended, the red collar easily slips forward, and will allow the retaining clips to be pushed inwards, allowing the switch to be removed

To access the switch, you need to remove the lower knee trim. Its held on with three screws (one under headlight switch in the square recess, one under the dial for cluster brightness, and the other above the clutch pedal)

Once that is removed, the switch is mounted above the brake pedal

To release the red collar, you need to push the pedal down, extend the plunger, and then slip the red collar out. Only then can you violently wiggle the switch around until it comes out of its bracket.

This isn’t an easy task to do. The trick is to either have the car engine running, or press the pedal down immediately after shutting the engine off, so that there is vacuum in the booster and the pedal can travel down far enough to allow the plunger to come out. A lot of people get stuck there, you cannot extend the plunger far enough if the pedal cannot be pushed down. I used a screwdriver to lever the plunger out, and then my hand slide the collar forward, whilst holding the pedal down with my other hand.

DO NOT release the brake pedal until you have the switch removed, or it will just push the plunger and collar back in thanks to the ratchet.

Once the switch is free, you can release the brake pedal and if you haven’t already, disconnect the wiring connector.

New and old side by side. There was a bit of wear on the end of the plunger, so despite not having a date stamp, I suspect its original.

To fit the new switch, ensure the plunger and collar is fully extended, push the brake pedal down (doesn’t need to be all the way like removal) and then push the switch into the bracket until it clicks in. Slip the red collar down towards the body so the switch can’t come out. Now release the pedal, and you should hear it ratchet the plunger in. Plug the switch in, and test. You shouldn’t have any warnings on Check Control now, and the brake lights should work when the key is ON, and pedal is pressed.

Reinstall the trim, and away you go. Done.