Possible reasons for the brake pedal to fail on a car with an automatic transmission:
Brake fluid leak:
* Check the brake fluid level in the reservoir.
* Inspect the system for leaks.
* Replace worn or damaged brake hoses, tubes or seals.
Failed master cylinder:
* It may leak or become clogged, causing loss of hydraulic pressure.
* Inspect the master cylinder for leaks or other signs of damage.
* If necessary, replace the brake master cylinder.
Faulty vacuum brake booster:
* The vacuum booster uses engine vacuum to increase pressure on the brake pedal.
* Check vacuum hoses for cracks or leaks.
* Check that the brake booster is operating correctly.
Worn brake pads or rotors:
*If the brake pads or rotors are severely worn, this can cause the pedal to travel longer and cause it to sink.
* Inspect and replace worn brake pads or rotors.
Problems with the anti-lock brake system (ABS) control system:
* A faulty ABS control unit or speed sensors may interfere with the braking system.
* Scan the system for ABS related trouble codes.
* Replace faulty ABS components if necessary.
Problems with torque converter:
* A faulty torque converter can cause system pressure to build up and cause the pedal to drop out.
* Check the transmission fluid level and torque converter condition.
* Replace the torque converter if necessary.
Other possible reasons:
* Air in the brake system
* Worn or damaged brake lines
*Faulty Transmission Control Module (TCM)
Actions:
* Stop in a safe place and turn off the engine.
* Check the brake fluid level and inspect the system for leaks.
* Try bleeding the brake pedal several times to remove air from the system.
* If the brake pedal still fails, do not attempt to continue driving and call a tow truck.
* Take the vehicle to a repair shop to diagnose and repair the problem.