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GreigM

Brake light switch replacement

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I've recently replaced my brake pedal switch to cure a PSM/ ABS failure warning problem. Its all gone fine and I've had no issues with it at all, but on a UK forum there is a dealer claiming you can't simply replace this $15 part instead "The brake light switch really needs setting up on a Porsche system tester as you need to reference the brake pressure in the system as to when the lights come on..! if the lights are on but not enough pressure then the system thinks there is a fault.".

Now as far as I understand it the switch is just that, an on/off indication of the pedal being pressed, so why would there be a variable element to do with the pressure being applied. I can understand there may be a setting for how much pressure is in the system before the lights come on, but I don't understand why the on/off switch would require this to be adjusted.

Can anyone help clarify?

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I moved this to the Boxster section since your profile (and signature) says Boxster.

Here is the process from the service manual:

Brake light switch setting

The switch travel of the brake light switch is designed so that the brake light lights up before braking pressure builds up. The switches are self-adjusting and are mounted in a bayonett lock in the pedal block by turning them through 90°. By way of its self-adjustment function, the switch compensates for the tolerances in the pedals during initial assembly. However, if the switch is "overpressed" during work on the pedals or on the brake unit, the switch travel or pedal travel up to the switching point is lost.

The consequence: The brake lights are always on or flicker when travelling over bumps. In vehicles with cruise control, the cruise control can be deactivated as a result of vehicle vibrations under certain circumstances. Therefore, the switches must be readjusted after any work in which the brake pedal is moved out of its "normal" position (for example, work on the pedals or on the brake unit).

Checking brake light switch setting (No. 1)

The pedal must move a perceptible distance of approx. 5 to 10 mm before the brake light lights up.

At the same time, check (make sure) that the brake light lights up before the pedal meets perceptible resistance or before brake pressure builds up.

Adjusting switch if pedal travel is too small

There are two possibilities to adjust the switch if the pedal travel to the switching point is too small.

1st possibility:

- Press the brake pedal and pull out the switch plunger.

- Release the pedal. Check adjustment

2nd possibility:

- Release switch by turning it 90° and pull it out of the installation opening.

- Pull operating plunger out of the switch as far as it will go.

- Reinstall the switch.

When installing the switch for the first time, it is essential to press it vertically against the bearing surface. It will otherwise not be possible to lock the switch (90° turn), even if great force is exerted.

Note: A play-free fit of the switch is no longer ensured after it has been installed and removed several times. The switch must be replaced by a new switch as soon as it perceptibly "wobbles" in its receiver.

Adjusting switch if pedal travel is too large

Press pedal and press plunger into the switch by one notch (audible click).

The pedal travel to the switching point then decreases by approx. 3... 4 mm.

Then check setting again.

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Apologies, its now a 2002 996 turbo, however as the pedal is the same I suppose the section makes no difference - so as far as I read the above, the PST is not required?

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No codes at all.

Yes, it fixed the problem straight away - was very pleased as it only cost about £10.

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This is interesting. I'm ready the adjustment and I am confused. Was it hard to adjust?

"- Release switch by turning it 90° and pull it out of the installation opening.

- Pull operating plunger out of the switch as far as it will go.

- Reinstall the switch."

Confusing, isn't it!

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The plunger is self adjusting. You remove the switch by twisting, pull the plunger out all the way (you can feel it kind of ratchet in you fingers) and then reinstall. When you push the pedal in the depth of the plunger adjusts itself to the correct travel needed.

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This really couldn't be easier to install - just locate the existing one, twist it 90 degrees to release it from the bracket then disconnect the wire - reconnect to new unit, put back into place and twist 90 degrees to lock into place. No adjustment necessary....

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When the switch is placed in his bracket, the brake pedal should be at rest, push not the the pedal simultaneously otherwise the adjusting will not properly set. The brake lights should be on before any brake pressure is build up.

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You mix the issues together: a faulty brake switch can cause an ABS/ PSM error, a faulty throttle body can cause an ABS/ PSM error, a faulty MAFcan cause an ABS/ PSM error, also the wiring's, connectors, ABS control box/unit and many more. On the other hand an ABS/ PSM problem cant give a MAF, throttle body or brake switch error.

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You mix the issues together: a faulty brake switch can cause an ABS/ PSM error, a faulty throttle body can cause an ABS/ PSM error, a faulty MAFcan cause an ABS/ PSM error, also the wiring's, connectors, ABS control box/unit and many more. On the other hand an ABS/ PSM problem cant give a MAF, throttle body or brake switch error.

Lots of error could be caused by faulty wiring in the car. As far as I am concerned, I really do believe that there would be no error if we would handle it with care. I think that the brake switch could be replaced immediately without having to do the tedious steps. I got my brake switch replaced 5 years ago and it still functions well.

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