Self-Diagnostic System: Introduction

The Hydraulic Brake Booster (HBB) accumulates the high pressure brake fluid in the accumulator by operating the pump motor. Even though the working sound of the pump motor can be heard during operation, this sound is usually generated at normal operation of the HBB and is not an indication of a malfunction.

HBB diagnostic trouble codes are set under different conditions, depending on the malfunction detected. Most HBB DTCs will only be set during vehicle operation. Some HBB DTCs will also be set during the HBB self-check immediately after the engine is started.

After erasing an HBB DTC, duplicate the HBB DTC set conditions to see if it resets. Depending on the detection timing and set conditions for the specific HBB DTC, you must either drive the vehicle or turn the engine off and restart it. To set the proper conditions for that DTC again, refer to DTC SET CONDITIONS for each HBB DTC that you are trying to reset.