Check Power Supply And Ground Circuit Of Backup Unit

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:

DC power supply circuit Ref. to WIRING SYSTEM>POWER SUPPLY CIRCUIT>WIRING DIAGRAM

Courtesy of SUBARU OF AMERICA, INC.

CHECK FUSE .
1. Turn the ignition switch to OFF.
2. Check the fuse on the upstream of the backup unit. Ref. to SECURITY AND LOCKS>RELAY AND FUSE>INSPECTION
Is the check result OK?

Yes : Go to 2.

No : Replace the defective fuse.
CHECK POWER SUPPLY .
1. Disconnect the backup unit connector.
2. Turn the ignition switch to ON.
3. Measure the voltage between backup unit connector and chassis ground.
  Connector & terminal
  
  (i112) No. 3 (+) - Chassis ground (-):
  
  (i112) No. 5 (+) - Chassis ground (-):
  
  (i112) No. 8 (+) - Chassis ground (-):
Is the voltage 9 V or more?

Yes : Go to 3.

No : Check the harness for open or short circuit between the backup unit and the fuse.
CHECK GROUND CIRCUIT .
Measure the resistance between backup unit connector and chassis ground.

Connector & terminal

(i112) No. 6 - Chassis ground:

Is the resistance less than 10 Ω?

Yes : The power supply and ground circuit are OK.

No : Repair or replace the defective part.