When you turn the engine on and depress the brake, the brake switch activates a cable pulley to free the lock pin on the shifter. The 'solenoid' seldom fails. The area by the shifter does get very dirty with dust and other debris and sometimes this is the fault. Unfortunately, exposing the cable under the shifter is a 1 hour job with lots of plastic pieces to get out of the way.

Use your ears when you press on the brake. You should hear a barely audible 'click' which is the solenoid moving. So long as you hear that noise, the brake pedal switch and solenoid are good and it is probably just dirt and a clogged spring mechanism.

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My back feels better when I sit in a Volvo seat