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: 

• EyeSight does not operate.
• Stop lights do not illuminate sometimes.

Wiring diagram: 

Vehicle stability control system Ref. to WIRING SYSTEM>VEHICLE STABILITY CONTROL SYSTEM .

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

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK DTC  .

   Read the DTC of [Brake Control] using the Subaru Select Monitor. Ref. to BRAKE CONTROL (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

   Are any DTCs related to the stop light switch displayed?

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

   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. 2 - No. 4 when the battery voltage is applied.

      Terminals 

      No. 1 - No. 3:

   Is the resistance less than 1 Ω?

   Yes:  Go to  3.

   No:  Replace the stop light relay. Ref. to VEHICLE STABILITY CONTROL>RELAY AND FUSE .

3. CHECK VSC (VDC) CONTROL MODULE & H/U CONNECTOR  .

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

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

   Yes:  Repair the VSC (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 

   (M/B) No. 1 - (F/B fuse) No. 4:

   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 

      (M/B) No. 1 (+) - 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 

      (M/B) No. 4 (+) - 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 

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

   Is the voltage 10 V or more?

   Yes:  Go to  8.

   No:  Repair the ignition power supply circuit.

8. CHECK VSC (VDC) CONTROL MODULE & H/U  .
   1. Turn the ignition switch to OFF.
   2. Connect all connectors and relays.
   3. Using the Subaru Select Monitor, perform the clear memory of [Brake Control]. Ref. to COMMON (DIAGNOSTICS)>CLEAR MEMORY .
   4. 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 VSC (VDC) Control Module & H/U. Ref. to VEHICLE STABILITY CONTROL>VSC (VDC) CONTROL MODULE AND HYDRAULIC CONTROL UNIT (VSCCM & H/U) .

   No:  Go to  9.

9. CHECK DETECTION OF OTHER DTCS FOR VSC (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.