DTC C1521: Motor Relay

DTC detecting condition: 

A fault is detected if the pump motor supply voltage becomes significantly low when the pump motor is not driven.

Trouble symptom: 

• ABS does not operate sometimes.
• VDC does not operate.
• Hill start assist does not operate. (Models without EyeSight)
• AVH does not function. (Models with EyeSight)
• EyeSight does not operate. (Models with EyeSight)

Wiring diagram: 

• Models without EyeSight

  Vehicle dynamics control system. Refer to WIRING SYSTEM>VEHICLE DYNAMICS CONTROL SYSTEM>WIRING DIAGRAM>WITHOUT EYESIGHT .

  Courtesy of SUBARU OF AMERICA, INC.

• Models with EyeSight

  Vehicle dynamics control system. Refer to WIRING SYSTEM>VEHICLE DYNAMICS CONTROL SYSTEM>WIRING DIAGRAM>WITH EYESIGHT .

  Courtesy of SUBARU OF AMERICA, INC.

1. CHECK VDC Control Module & H/U INPUT VOLTAGE. 
   1. Turn the ignition switch to OFF.
   2. Disconnect the connector from the VDC Control Module & H/U.
   3. Turn the ignition switch to ON.
   4. Measure the voltage between VDC Control Module & H/U connector and chassis ground.

      Connector & terminal 

      Models without EyeSight 

      (B310) No. 1 (+) - Chassis ground (-):

      (B310) No. 6 (+) - Chassis ground (-):

      Models with EyeSight 

      (B310) No. 1 (+) - Chassis ground (-):

      (B310) No. 35 (+) - Chassis ground (-):

   Is the voltage 10 - 15 V?

   Yes:  Go to  2.

   No:  Repair the VDC Control Module & H/U power supply circuit.

2. CHECK VDC Control Module & H/U INPUT VOLTAGE. 

   Calculate the voltage difference measured in step 1.

   • Models without EyeSight
     1. (B310) No. 1 (+) - Chassis ground (-):
     2. (B310) No. 6 (+) - Chassis ground (-):
   • Models with EyeSight
     1. (B310) No. 1 (+) - Chassis ground (-):
     2. (B310) No. 35 (+) - Chassis ground (-):

   Is the voltage difference between A and B 2 V or more?

   Yes:  Repair the power supply circuit.

   No:  Go to  3.

3. CHECK INSTALLATION OF VDC Control Module & H/U GROUND. 

   Is the VDC Control Module & H/U ground terminal installation bolt (ground bolt fixing onto the side frame upper face) installed correctly?

   Yes:  Go to  4.

   No:  Install the VDC Control Module & H/U ground terminal installation bolt correctly.

4. CHECK VDC Control Module & H/U GROUND CIRCUIT (CHECK FOR OPEN CIRCUIT). 
   1. Turn the ignition switch to OFF.
   2. Measure the resistance between VDC Control Module & H/U connector and chassis ground.

      Connector & terminal 

      Models without EyeSight 

      (B310) No. 13 - Chassis ground:

      Models with EyeSight 

      (B310) No. 14 - Chassis ground:

   Is the resistance less than 10 Ω?

   Yes:  Go to  5.

   No:  Repair the VDC Control Module & H/U ground harness.

5. CHECK VDC Control Module & H/U MOTOR RELAY. 

   Measure the resistance between VDC Control Module & H/U terminals.

   Terminals 

   Models without EyeSight 

   No. 1 - No. 13:

   Models with EyeSight 

   No. 1 - No. 14:

   Is the resistance 1 Ω or more?

   Yes:  Go to  6.

   No:  Replace the VDC Control Module & H/U. Refer to VEHICLE DYNAMICS CONTROL (VDC)>VDC CONTROL MODULE AND HYDRAULIC CONTROL UNIT (VDC Control Module & H/U) .

6. CHECK POOR CONTACT OF CONNECTORS. 

   Turn the ignition switch to OFF.

   Is there poor contact of connector between generator, battery and VDC Control Module & H/U?

   Yes:  Repair the connector.

   No:  Go to  7.

7. CHECK VDC Control Module & H/U. 
   1. Connect all connectors.
   2. Perform the Clear Memory Mode. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>CLEAR MEMORY MODE .
   3. Perform the Inspection Mode. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>INSPECTION MODE .
   4. Read the DTC. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>READ DIAGNOSTIC TROUBLE CODE (DTC) .

   Is the same DTC displayed?

   Yes:  Replace the VDC Control Module & H/U. Refer to VEHICLE DYNAMICS CONTROL (VDC)>VDC CONTROL MODULE AND HYDRAULIC CONTROL UNIT (VDC Control Module & H/U) .

   No:  Go to  8.

8. CHECK DETECTION OF OTHER DTCS FOR VDC. 

   Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>READ DIAGNOSTIC TROUBLE CODE (DTC) .

   Is any other DTC displayed?

   Yes:  Perform the diagnosis according to DTC. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>LIST OF DIAGNOSTIC TROUBLE CODE (DTC) .

   No:  Currently, it is normal. There may have been a temporary poor contact in the harness and connector or a temporary noise interference.