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.

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.

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.
CHECK HARNESS (CHECK FOR OPEN CIRCUIT) .
1. Turn the ignition switch to OFF.
2. Disconnect the connectors from the VDC Control Module & H/U and parking brake switch.
3. Measure the resistance between VDC Control Module & 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 VDC Control Module & H/U and parking brake switch connector.
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 VDC Control Module & H/U and parking brake switch connector.
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 VDC Control Module & H/U and parking brake switch connector.
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
CHECK VDC Control Module & 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 VDC Control Module & H/U. Ref. to VEHICLE DYNAMICS CONTROL (VDC)>VDC CONTROL MODULE AND HYDRAULIC CONTROL UNIT (VDC CONTROL MODULE & H/U)

No : Go to 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.