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 Ref. to WIRING SYSTEM>ELECTRIC POWER STEERING SYSTEM

Courtesy of SUBARU OF AMERICA, INC.

NOTE:

If power supply voltage failure exists at the vehicle side, the warning light goes off if the normal voltage returns.

CHECK BATTERY .
Check the battery. Ref. to STARTING/CHARGING SYSTEMS (H4DOTC)>BATTERY>INSPECTION

Is the check result OK?

Yes : Go to 2.

No : Charge or replace the battery. Ref. to STARTING/CHARGING SYSTEMS (H4DOTC)>BATTERY
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.
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.
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.
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. Ref. to POWER ASSISTED SYSTEM (POWER STEERING)>ELECTRIC POWER STEERING GEARBOX

No : Repair or replace the harness.