Method for checking the function of a brake system with a brake booster

1. A method for checking a functioning of a brake system of a vehicle with an internal combustion engine and a brake booster, the brake booster operating with under-pressure as auxiliary energy, and a pressure sensor disposed in an under-pressure region of the brake system, which comprises the steps of:

sensing a brake pressure during a braking process of the vehicle;

storing an output signal of the pressure sensor in a memory before a start of the braking process if the brake pressure is within a predefined first pressure range;

after an ending of the braking process, forming a difference from a current output signal of the pressure sensor and the output signal stored in the memory; and

evaluating the difference to determine a functioning of the brake system.

2. The method according to claim 1 , which further comprises:

comparing the difference with a predefined first threshold value; and

suspecting a fault if the difference is smaller than the predefined first threshold value.

3. The method according to claim 2 , which further comprises increasing a value of a diagnostic counter if at least one of a fault is suspected and the difference is smaller than the first threshold value.

4. The method according to claim 2 , which further comprises reducing a value of a diagnostic counter if the difference is greater than or equal to the first threshold value.

5. The method according to claim 3 , which further comprises performing at least one of:

making an entry in a fault memory; and

outputting a fault signal if the value of the diagnostic counter is greater than a predefined second threshold value.

6. The method according to claim 1 , which further comprises carrying out the method only if the vehicle is within a predefined speed region at the start of the braking process.

7. The method according to claim 1 , which further comprises carrying out the method only if more time than a predefined minimum period has passed between an end of a last preceding braking process and a start of a next braking process.

8. The method according to claim 1 , which further comprises determining a time period within which the pressure sensor outputs, after a start of the internal combustion engine, the output signal which corresponds to a pressure which is below a pressure limiting value.

9. The method according to claim 8 , which further comprises outputting a fault message if the time period is greater than a third threshold value.

10. The method according to claim 8 , which further comprises outputting a fault message via a control unit only if a braking process has not taken place during a determination of the time period.

11. The method according to claim 1 , which further comprises checking the output signal of the pressure sensor to determine whether it is electrically satisfactory.

12. The method according to claim 1 , which further comprises evaluating the difference to determine a function of the under-pressure region.

13. An open-loop and/or closed-loop control device, comprising:

a controller programmed to:

sense a brake pressure during a braking process of a vehicle;

store an output signal of a pressure sensor in a memory before a start of a braking process if the brake pressure is within a predefined first pressure range;

after an ending of the braking process, form a difference from a current output signal of the pressure sensor and the output signal stored in the memory; and

evaluate the difference to determine a functioning of a brake system.

14. A computer-readable medium having computer-executable instructions for performing a method which comprises the steps of:

sensing a brake pressure during a braking process of a vehicle;

storing an output signal of a pressure sensor in a memory before a start of a braking process if the brake pressure is within a predefined first pressure range;

after an ending of the braking process, forming a difference from a current output signal of the pressure sensor and the output signal stored in the memory; and

evaluating the difference to determine a functioning of a brake system.