DTC C1921: Parking Position Switch Circuit

DTC detecting condition: 

• A fault is detected if the switch was positioned at lock or release continuously for 300 seconds while the vehicle is stopped.
• A fault is detected if an irregular switch condition continues for a predetermined period of time immediately after the switch position is changed. A fault is also detected if the switch condition is not confirmed afterwards.
• A fault is detected if the switch harness is open or shorted.

Trouble symptom: 

Parking brake system does not operate.

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: 

Parking brake/brake fluid level warning light system Ref. to WIRING SYSTEM>PARKING BRAKE/BRAKE FLUID LEVEL WARNING LIGHT SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK OPERATION OF ELECTRONIC PARKING BRAKE  .

   Operate the parking brake switch.

   Does the electronic parking brake operate properly?

   Yes:  Ask the customer whether the following switch operation was performed.

   • Operated slowly over one second or more.
   • Repeated ON/OFF operation several times within one second.

   When the case above is true, the system is normal.

   When it is normal, a temporary poor contact or noise interference is a possible cause.

   No:  GO TO  2.

2. CHECK HARNESS (CHECK FOR OPEN CIRCUIT)  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the connectors from the VDCCM & H/U and parking brake switch.
   3. Measure the resistance between VDCCM & H/U and parking brake switch connector.

      Connector & terminal 

      (B66) No. 15 - (C31) No. 5:

      (B66) No. 16 - (C31) No. 4:

      (B66) No. 31 - (C31) No. 2:

      (B66) No. 32 - (C31) No. 1:

   Is the resistance less than 1 Ω?

   Yes:  GO TO  3.

   No:  Repair harness and connector between VDCCM & H/U and parking brake switch connector.

3. CHECK HARNESS (CHECK FOR GROUND SHORT CIRCUIT)  .

   Measure the resistance between the parking brake switch connector and chassis ground.

   Connector & terminal 

   (C31) No. 5 - Chassis ground:

   (C31) No. 4 - Chassis ground:

   (C31) No. 2 - Chassis ground:

   (C31) No. 1 - Chassis ground:

   Is the resistance 1 MΩ or more?

   Yes:  GO TO  4.

   No:  Repair ground short of harness between VDCCM & H/U and parking brake switch connector.

4. CHECK HARNESS (CHECK FOR SHORT CIRCUIT TO POWER SUPPLY)  .
   1. Turn the ignition switch to ON.
   2. Measure the voltage between parking brake switch connector and chassis ground.

      Connector & terminal 

      (C31) No. 5 (+) - Chassis ground (-):

      (C31) No. 4 (+) - Chassis ground (-):

      (C31) No. 2 (+) - Chassis ground (-):

      (C31) No. 1 (+) - Chassis ground (-):

   Is the voltage less than 1 V?

   Yes:  GO TO  5.

   No:  Repair short to power supply of harness between VDCCM & H/U and parking brake switch connector.

5. CHECK PARKING BRAKE SWITCH  .

   Check the parking brake switch. Ref. to PARKING BRAKE>PARKING BRAKE SWITCH>INSPECTION .

   Is the check result OK?

   Yes:  GO TO  6.

   No:  Replace the parking brake switch. Ref. to PARKING BRAKE>PARKING BRAKE SWITCH .

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