DTC C1751: Brake Boost Gauge Sensor

DTC detecting condition: 

• A fault is detected if the power supply to the brake vacuum pressure sensor is abnormal.
• A fault is detected if the communication signal from the brake vacuum pressure sensor is abnormal.

Trouble symptom: 

Brake assist function is not activated when vacuum pressure drops.

Wiring diagram: 

Vehicle dynamics control system Ref. to WIRING SYSTEM>VEHICLE DYNAMICS CONTROL SYSTEM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK BRAKE BOOSTER PRESSURE SENSOR POWER SUPPLY  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the connector from the brake booster pressure sensor.
   3. Turn the ignition switch to ON.
   4. Measure the voltage between brake booster pressure sensor connector terminals.

      Connector & terminal 

      (B100) No. 1 (+) - (B100) No. 2 (-):

   Is the voltage 4.9 - 5.1 V?

   Yes:  Go to  3.

   No:  Go to  2.

2. CHECK BRAKE BOOSTER PRESSURE SENSOR POWER SUPPLY SYSTEM  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the connector from the VDCCM & H/U.
   3. Measure the resistance between the VDCCM & H/U and the brake booster pressure sensor connector.

      Connector & terminal 

      (B66) No. 20 - (B100) No. 1:

      (B66) No. 28 - (B100) No. 2:

   Is the resistance less than 1 Ω?

   Yes:  Go to  3.

   No:  Repair the harness connector between the VDCCM & H/U and the brake booster pressure sensor.

3. CHECK BRAKE BOOSTER PRESSURE SENSOR SIGNAL SYSTEM  .

   Measure the resistance between the VDCCM & H/U connector and the brake booster pressure sensor.

   Connector & terminal 

   (B66) No. 45 - (B100) No. 3:

   Is the resistance less than 1 Ω?

   Yes:  Replace the brake booster. Ref. to BRAKE>BRAKE BOOSTER .

   No:  Repair the harness connector between the VDCCM & H/U and the brake booster pressure sensor.