DTC C1572: Brake Lamp Relay On Stuck

DTC Detecting condition: 

Defective stop light relay signal

Trouble symptom: 

• Hill descent control does not operate. (Model with X mode)
• EyeSight does not operate. (Model with EyeSight)
• Brake lights do not go off sometimes.

Wiring diagram: 

Stop light system Ref. to WIRING SYSTEM>STOP LIGHT SYSTEM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK FUSE. 
   1. Turn the ignition switch to OFF.
   2. Check F/B fuse (No. 10).

      Is the fuse blown out?

      Yes:  Replace F/B fuse (No. 10).

      No:  Go to  2.

2. CHECK STOP LIGHT RELAY. 

   Measure the resistance between brake light relay terminals.

   Terminals 

   No. 6 - No. 8:

   Is the resistance less than 1 Ω?

   Yes:  Go to  3.

   No:  Replace the stop light relay.

3. CHECK VDC Control Module & H/U CONNECTOR. 

   Disconnect the connector from the VDC Control Module & H/U.

   Is there poor contact or damage of the VDC Control Module & H/U connector?

   Yes:  Repair the VDC Control Module & H/U connector.

   No:  Go to  4.

4. CHECK STOP LIGHT RELAY CIRCUIT. 

   Measure the resistance between the stop light relay and the fuse or the VDC Control Module & H/U connector.

   Connector & terminal 

   (B225) No. 6 - (B310) No. 33:

   (B225) No. 8 - (F/B fuse) No. 10:

   Is the resistance less than 1 Ω?

   Yes:  Go to  5.

   No:  Repair the stop light relay circuit.

5. CHECK STOP LIGHT RELAY CIRCUIT. 
   1. Connect all connectors.
   2. Turn the ignition switch to ON.
   3. Measure the voltage between stop light relay and chassis ground.

      Connector & terminal 

      (B225) No. 8 (+) - Chassis ground (-):

      Is the voltage 10 V or more?

      Yes:  Go to  6.

      No:  Repair the stop light relay circuit.

6. CHECK VDC Control Module & H/U. 
   1. Using the Subaru Select Monitor, perform the clear memory. Ref. to COMMON (DIAG)>CLEAR MEMORY .
   2. Execute the inspection mode. Ref. to BRAKE CONTROL (DIAGNOSTICS)>INSPECTION MODE .
   3. Read the DTC using Subaru Select Monitor. Ref. to BRAKE CONTROL (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

      Is the same DTC displayed?

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

      No:  Go to  7.

7. CHECK DETECTION OF OTHER DTCS FOR VDC. 

   Read the DTC using Subaru Select Monitor. Ref. to BRAKE CONTROL (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

   Is any other DTC displayed?

   Yes:  Perform the diagnosis according to the DTC. Ref. to BRAKE CONTROL (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC)>LIST .

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