Check Power Supply And Ground Circuit Of Backup Unit

CHECK FUSE AND RELAY.
1. Turn the ignition switch to OFF.
2. Check the fuse on the upstream of the backup unit. Refer 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. Measure the voltage between backup unit connector and chassis ground.
Connector & terminal

(i313) No. 3 (+) - Chassis ground (-):

(i313) No. 5 (+) - Chassis ground (-):

(i313) 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

(i313) 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 harness.