How to Solve the Problem of Unable to Press the Brake in an Automatic Transmission Car?

[LaylaMarie]

If the brake in an automatic transmission car cannot be pressed down when starting, it is likely due to a lack of vacuum assistance, and you may need to apply more force. If this doesn't work, the issue might be with the switch, which can be resolved by replacing it. In driving, to prevent unexpected situations such as sudden movement or rolling when igniting the vehicle, automatic transmission models are designed to require pressing the brake for ignition. If the brake is not pressed, the car cannot successfully start. Reasons for the brake being hard to press: 1. The car's vacuum booster pump is leaking or malfunctioning. It's important to note that the force applied to the brake pedal is amplified by the brake booster pump. If it fails, the brake loses its main force, making it difficult to press. 2. Pressing the brake after the engine is turned off, which is also related to the brake booster pump. The brake booster pump continuously generates vacuum only when the engine is running. When the engine is off, it relies on the residual vacuum assistance, which usually depletes after a few presses. However, this condition is not a fault and will recover after the engine is started.

[SanJoshua]

Last time I drove my relative's automatic transmission car, I also encountered a situation where the brake pedal was very stiff. Right after starting the car, I almost stepped my foot numb but still couldn't brake properly, which scared me so much that I immediately turned off the engine and restarted it. Later, an experienced mechanic told me that after turning off the engine, the brake booster pump stops working. In such cases, don't force the pedal; instead, start the car and wait a few seconds for the booster to recover. If the brake pedal still feels hard after starting, you should quickly check whether there's a vacuum leak or if the brake fluid level is sufficient, as air in the brake lines can also cause this. Once, my friend's car had a torn brake master cylinder seal, and after replacing it, the pedal immediately became much lighter. Remember, as soon as the brake pedal feels abnormal, pull over immediately and call for assistance—continuing to drive is too dangerous!

[MacMatteo]

We female drivers fear brake failure the most. If you find the brake pedal hard to press, don't panic—try quickly pumping it twice, as sometimes this can restore some assist. Last month, my brakes were unusually stiff right after starting the car, and it turned out the floor mat was jamming the pedal. If the pedal remains hard to press while the engine is running, it's likely a vacuum booster failure—never drive the car before fixing this. Remember to change the brake fluid every two years, as degraded fluid can form bubbles and affect pedal feel. A 4S shop technician once mentioned that modern cars have brake override systems, which stop the car even if both accelerator and brake are pressed, but this is only for emergencies—proper repairs are still essential.

[VanCollin]

As a veteran driver with over 300,000 kilometers under my belt, I've seen plenty of brake issues. It's normal for an automatic transmission car's brake pedal to become stiff after a few pumps before starting due to vacuum loss. However, there are three scenarios when the brake pedal becomes hard to press while driving: if the booster pump belt breaks, you'll hear a hissing air leak sound; if the brake fluid is low, the dashboard warning light will illuminate; the most troublesome is when the booster diaphragm ruptures, requiring full-body force to barely slow down. Once, my car's brakes became heavy after heavy rain, and troubleshooting revealed the wheel speed sensor was waterlogged and malfunctioning. I recommend keeping an OBD scanner in your car—just scan the fault code to identify the issue.