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Hydraulic brake booster / ABS control unit faults

A combined Hydraulic Brake Booster & ABS control unit is fitted to many vehicles including the following:

  • Toyota Landcruiser 100 series
  • Toyota Landcruiser Prado 120 / 150 series
  • Lexus LX 100 series
  • Lexus GS / SC series
  • Mitsubishi Pajero NM-NW series

These Aisin and Advics units do not use the traditional vacuum assisted brake booster instead they incorporate a hydraulic brake booster with accumulator to store hydraulic pressure when needed. When these units fail the brake pedal feels hard and the driver no longer has assisted brakes.  This can become a very dangerous situation.

Common faults include:

  • The abs warning light & buzzer activates
  • The brake pedal goes hard
  • Pump motor failure
  • Hydraulic brake booster pump motor open malfunction, fault code C1251
  • Hydraulic brake booster pump on time abnormal long, fault code C1252
  • Accumulator low pressure malfunction, fault code C1256
  • Accumulator pressure system malfunction, fault code 57 (Mitsubishi)


Injectronics can offer a cost effect and time saving alternative to purchasing a complete new unit.  We can repair the customers own unit for the above listed faults. This also guarantees that no programming is required upon refitting of the unit. Every remanufactured unit is returned to customer with detailed bleeding instructions to follow upon reinstallation.

Important removal instructions:

  • Before removing the unit from the vehicle, check and record all fault codes.  These codes must be supplied with any other diagnostic information.
  • Drain ALL brake fluid from the reservoir and seal fluid holes in the block.
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