Check For Short To Power Supply (Power Unit Can)

WARNING: This page is about a different car, the 2022 Subaru WRX. However, it is still accessible from the selected car via links, so may be relevant.

Wiring diagram:

CAN communication system Ref. to WIRING SYSTEM>CAN COMMUNICATION SYSTEM>WIRING DIAGRAM

Courtesy of SUBARU OF AMERICA, INC.

NOTE:

Main wiring harness or related lines may be shorted to battery circuit, or shorted to battery circuit in one of the control modules.

CHECK BETWEEN RELATED LINES AND MAIN WIRING HARNESS .
1. Turn the ignition switch to OFF.
2. Disconnect the central gateway control module connector.
3. Turn the ignition switch to ON.
4. Using a tester, measure the voltage between the central gateway control module connector and chassis ground.
  Connector & terminal
  
  (i88) No. 23 (+) - Chassis ground (-):
  
  (i88) No. 24 (+) - Chassis ground (-):
Is the voltage 5 V or less?

Yes : Go to 3.

No : Go to 2.
CHECK CONTROL MODULE .
With a tester connected, disconnect control modules in order.

Connector & terminal

(i88) No. 23 (+) - Chassis ground (-):

(i88) No. 24 (+) - Chassis ground (-):

Did the voltage change to 5 V or less?

Yes : Replace the control module whose voltage has changed.

No : Repair or replace the short circuit of the harness between the central gateway control module and ECM.
CHECK CENTRAL gateway control module .
1. Connect the central gateway control module connector.
2. Disconnect the VDC Control Module connector.
3. Using a tester, measure the voltage between the VDC Control Module connector and chassis ground.
  Connector & terminal
  
  (B66) No. 5 (+) - Chassis ground (-):
  
  (B66) No. 19 (+) - Chassis ground (-):
Is the voltage 5 V or less?

Yes : Currently, it is normal.

No : Replace the central gateway control module. Ref. to BODY CONTROL/COMMUNICATION SYSTEM>CENTRAL gateway control module