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.
• Stop lights do not go off sometimes.

Failure detection pattern: 

• "Primary" (high-priority diagnosis)

Warning light/indicator light: 

The combination of DTC and warning light display may differ from the list depending on vehicle conditions and driving conditions at the time of failure detection.

• ABS warning light -
• VDC warning light & VDC operation indicator light -
• Electronic parking brake warning light (red) -
• Brake warning light (EBD warning light) (red) -

Wiring diagram: 

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

Fuse and relay Ref. to WIRING SYSTEM>FUSE AND RELAY>LOCATION .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK FUSE  .
   1. Turn the ignition switch to OFF.
   2. Check the M/B fuse (No. 14).

   Is the fuse blown out?

   Yes:  Replace the M/B fuse (No. 14).

   No:  GO TO  2.

2. CHECK STOP LIGHT RELAY  .

   Measure the resistance of stop light relay terminals.

   Terminals 

   No. 2 - No. 4:

   Is the resistance less than 1 Ω?

   Yes:  GO TO  3.

   No:  Replace the stop light relay.

3. CHECK VDCCM & H/U CONNECTOR  .

   Disconnect the connector from the VDCCM & H/U.

   Is there poor contact or damage of the VDCCM & H/U connector?

   Yes:  Repair the VDCCM & 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 VDCCM & H/U connector.

   Connector & terminal 

   (M/B) No. 4 - (B66) No. 33:

   (M/B) No. 2 - (M/B fuse) No. 14:

   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 

      (M/B) No. 2 (+) - Chassis ground (-):

   Is the voltage 10 V or more?

   Yes:  GO TO  6.

   No:  Repair the stop light relay circuit.

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

   Is the same DTC displayed?

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

   No:  GO TO  7.

7. CHECK DETECTION OF OTHER DTCS FOR VDC  .

   Read the DTC of [Brake Control] using the 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.