DTC C1571: Brake Lamp Relay Off Stuck

DTC detecting condition: 

A fault is detected if the stop light relay operation request were compared with the feedback signal and detected as follows:

• The feedback signal is OFF.
• The stop light relay operation request is ON.

Trouble symptom: 

• AVH does not function. (Models with EyeSight)
• EyeSight does not operate. (Models with EyeSight)
• Stop lights do not illuminate sometimes.
• Electronic parking brake warning light illuminates.

Wiring diagram: 

Stop light system. Refer to WIRING SYSTEM>STOP LIGHT SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK DTC. 

   Check the DTC using Subaru Select Monitor. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>READ DIAGNOSTIC TROUBLE CODE (DTC) .

   Are any DTCs related to the stop light switch displayed?

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

   No:  Go to  2.

2. CHECK STOP LIGHT RELAY. 
   1. Turn the ignition switch to OFF.
   2. Remove the stop light relay.
   3. Measure the resistance between stop light relay terminals No. 8 - No. 6 when the battery voltage is applied.

      Terminals 

      No. 9 - No. 10:

   Is the resistance less than 1 Ω?

   Yes:  Go to  3.

   No:  Replace the stop light relay. Refer to VEHICLE DYNAMICS CONTROL (VDC)>RELAY AND FUSE .

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 SWITCH CIRCUIT. 

   Measure the resistance between the stop light relay and the fuse.

   Connector & terminal 

   (B567) No. 9 - (F/B fuse) No. 8:

   Is the resistance less than 1 Ω?

   Yes:  Go to  5.

   No:  Repair or replace the open circuit in the power supply circuit including the fuse.

5. CHECK STOP LIGHT SWITCH 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 

      (B567) No. 9 (+) - Chassis ground (-):

   Is the voltage 10 V or more?

   Yes:  Go to  6.

   No:  Repair or replace the open circuit in the power supply circuit including the fuse.

6. CHECK STOP LIGHT RELAY CIRCUIT. 
   1. Turn the ignition switch to OFF.
   2. Remove the stop light relay.
   3. Turn the ignition switch to ON.
   4. Measure the voltage between stop light relay and chassis ground.

      Connector & terminal 

      (B567) No. 6 (+) - Chassis ground (-):

   Is the voltage 10 V or more?

   Yes:  Repair the stop light relay circuit.

   No:  Go to  7.

7. CHECK STOP LIGHT RELAY CIRCUIT. 

   Measure the voltage between stop light relay and chassis ground.

   Connector & terminal 

   (B567) No. 8 (+) - Chassis ground (-):

   Is the voltage 10 V or more?

   Yes:  Go to  8.

   No:  Repair the ignition power supply circuit.

8. CHECK VDC Control Module & H/U. 
   1. Turn the ignition switch to OFF.
   2. Connect all connectors and relays.
   3. Perform the Clear Memory Mode. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>CLEAR MEMORY 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  9.

9. 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.