DTC C2551: Power Supply Relay

DTC detecting condition: 

• When short malfunction of power supply relay is detected at initial check.
• When power supply voltage failure is detected after the ignition switch is ON.
• When power supply voltage drop is detected with 500 rpm engine speed reception.

Trouble symptom: 

• The steering wheel operation feels heavy.
• STEERING warning light illuminates.

Wiring diagram: 

Electric power steering system Refer to WIRING SYSTEM>Electric Power Steering System .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK BATTERY  .

   Check the battery. Refer to STARTING/CHARGING SYSTEMS (H4DO)>BATTERY>INSPECTION . Refer to STARTING/CHARGING SYSTEMS (H4DOTC)>Battery>INSPECTION .

   Is the check result OK?

   Yes  : Go to  2.

   No  : Charge or replace the battery.

2. CHECK BATTERY TERMINAL AND FUSE  .

   Check the battery terminals and the fuse.

   Is the check result OK?

   Yes  : Go to  3.

   No  : Repair or replace faulty parts.

3. CHECK WIRING HARNESS  .
   1. Disconnect the connector. (B21, B52)
   2. Turn the ignition switch to ON.
   3. Using a tester and special tool harness, check the voltage between terminals.

      Connector & terminal 

      (B21) No. 2 (+) - Chassis ground (-):

      Is the voltage 12 V or more?

      Yes  : Go to  4.

      No  : Repair the open circuit of harness or the poor contact of connector between the power steering control module and the battery.

4. CHECK GROUND CIRCUIT  .
   1. Turn the ignition switch to OFF.
   2. Using a tester and special tool harness, check the resistance between terminals.

      Connector & terminal 

      (B21) No. 1 - Chassis ground:

      Is the resistance less than 1 Ω?

      Yes  : Go to  5.

      No  : Repair the open circuit or poor contact of the harness between the power steering control module and chassis ground.

5. CHECK HARNESS  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the power steering control module connector (B76).
   3. Using a tester and special tool harness, check the resistance between harness terminals.

      Connector & terminal 

      (B52) No. 1 - (B76) No. 1:

      (B52) No. 2 - (B76) No. 2:

      Is the resistance less than 1 Ω?

      Yes  : Replace the steering gearbox. Refer to POWER ASSISTED SYSTEM (POWER STEERING)>Electric Power Steering Gearbox .

      No  : Repair or replace the harness.