02/07/2024
LETS TALK ABOUT THE ACCUMULATOR PUMP!!!!
C1391 - Abnormal leak in accumulator
C1252 - Booster pump motor on abnormally long
C1356 - Accumulator low pressure
These Diagnostic Trouble Codes (DTCs) are commonly encountered in Toyota hybrid braking systems, yet many owners are unfamiliar with their meanings, causes, and prevention methods. This discussion focuses on the Accumulator Pump, one part of a two-part system, with the Master Cylinder's role to be addressed separately.
The brake Accumulator Pump is crucial for maintaining hydraulic pressure in the braking system, ensuring prompt and efficient brake response. It consists of two main components: the ABS Hydraulic Pump and the Accumulator.
The ABS Hydraulic Pump generates brake fluid pressure, which is stored in the Accumulator. This pump operates with redundancy, powered by two motor relays. If one relay or fuse fails, the other ensures continuous fluid pressure.
The Accumulator is a nitrogen-filled steel vessel with a diaphragm, capable of storing hydraulic fluid under high pressure for immediate release as needed.
Several factors contribute to the malfunction indicated by these codes. A common issue in Toyota/Lexus hybrids is leakage from the Master Cylinder Unit, sometimes referred to as the "Hiss of Death." Over time, seals and gaskets wear out, leading to pressure loss in the unit.
Mechanical problems in the hydraulic pump can also cause issues, such as worn carbon brushes, faulty internal bearings, or excessive carbon buildup. These conditions can trigger the ABS system's fail-safe mode, resulting in a firm brake pedal feel.
According to the Toyota Service Manual, replacing both the Master Cylinder and the Accumulator Pump is recommended to address these issues effectively.