DTC C1571 Brake Lamp Relay Off Stuck: Wiring diagram

Stop light system Ref. to WIRING SYSTEM>Stop Light System>WIRING DIAGRAM>EXCEPT FOR MODEL WITHOUT EyeSight AND X MODE .

Fig 1: Stop Light System Wiring Diagram (Brake Lamp Relay OFF Stuck)

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK DTC. 

   Check the DTC using Subaru Select Monitor. Ref. to BRAKE CONTROL (DIAGNOSTICS)>Read Diagnostic Trouble Code (DTC) .

   Are any DTCs related to the stop light switch displayed?

   • Yes  : Perform the diagnosis according to DTC. Ref. to BRAKE CONTROL (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. 14 - No. 16 when the battery voltage is applied.

      Terminals 

      No. 17 -No. 18:

   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 SWITCH CIRCUIT. 

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

   Connector & terminal 

   (B564) No. 17 - (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 

      (B564) No. 17 (+) - 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 

      (B564) No. 14 (+) - 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 

   (B564) No. 16 (+) - Chassis ground (-):

   Is the voltage 10 V or more?

   • Yes  : Go to 8. 
   • No  : Repair the ignition power supply circuit.
8. CHECK VDCCM&H/U. 
   1. Turn the ignition switch to OFF.
   2. Connect all connectors and relays.
   3. Clear the memory. Ref. to BRAKE CONTROL (DIAGNOSTICS)>Clear memory .
   4. Read the DTC. Ref. to BRAKE CONTROL (DIAGNOSTICS)>Read Diagnostic Trouble Code (DTC) .

   Is the same DTC displayed?

   • Yes  : Replace the VDCCM only. Ref. to VEHICLE DYNAMICS CONTROL (VDC)>VDC Control Module and Hydraulic Control Unit (VDCCM&H/U)>REPLACEMENT .
   • No  : Go to 9. 
9. CHECK DETECTION OF OTHER DTCS FOR VDC. 

   Ref. to BRAKE CONTROL (DIAGNOSTICS)>Read Diagnostic Trouble Code (DTC) .

   Is any other DTC displayed?

   • Yes  : Perform the diagnosis according to DTC. Ref. to BRAKE CONTROL (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.