Circuit/System Verification

Ignition ON.
Verify that DTCs P0556, P0557, or P0558 are not set.
- If the DTC is set
  Refer to DTC P0556, P0557, or P0558 .
- Go to next step: If the DTC is not set
Has the Brake Assist System Diagnosis been performed.
- If the Brake Assist System Diagnosis has not been performed
  Refer to Brake Assist System Diagnosis .
- Go to next step: If the Brake Assist System Diagnosis has been performed
Test or replace the B19B Brake Booster Vacuum Sensor.
Verify the DTC does not set while operating the vehicle under the Conditions for Running the DTC.
- If the DTC sets
  Replace the K20 Engine Control Module.
- Go to next step: If the DTC does not set
All OK.