CAN Communication Circuit Check: Procedure: Diag-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.

Trouble causes:

DIAG-CAN communication circuit is shorted to ground.
DIAG-CAN communication circuit is shorted to power supply.
DIAG-CAN communication circuit is shorted between lines.
Central gateway control module malfunction

Wiring diagram:

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

Courtesy of SUBARU OF AMERICA, INC.

CAUTION:

Before performing diagnosis, refer to "CAUTION" in "General Description". Ref. to LAN SYSTEM (DIAGNOSTICS)>GENERAL DESCRIPTION>CAUTION

NOTE:

When measuring the resistance of CAN communication circuit, measure it in sleep status.

To enter sleep status

With ignition switch OFF and key or switch operation stopped, keep the doors and trunk all closed for one minute or more.
On model with the keyless access with push button start, keep the access key 2 m or more away from the vehicle.

CHECK BASIC DIAGNOSTIC PROCEDURE .
Check that the basic diagnosis has been performed up to STEP 3.

NOTE:
Possible defective parts can be narrowed easily by inspection using Subaru Select Monitor before performing "CHECK CAN COMMUNICATION CIRCUIT" using a tester.

Was the basic diagnostic procedure performed?

Yes : Go to 2.

No : Perform the basic diagnostic procedure. Ref. to LAN SYSTEM (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE
CHECK FOR SHORT TO GROUND IN HARNESS BETWEEN DATA LINK CONNECTOR AND CENTRAL gateway control module .
1. Turn the ignition switch to OFF.
2. Disconnect the central gateway control module connector.
3. Using the tester, measure the resistance between data link connector and chassis ground.
  Connector & terminal
  
  (i221) No. 6 - Chassis ground:
  
  (i221) No. 14 - Chassis ground:
Is the resistance less than 10 Ω?

Yes : Repair or replace the short circuit to ground of the harness between the data link connector and central gateway control module.

No : Go to 3.
CHECK FOR SHORT TO POWER SUPPLY IN HARNESS BETWEEN DATA LINK CONNECTOR AND CENTRAL gateway control module .
1. Turn the ignition switch to ON.
2. Using the tester, measure the voltage between data link connector and chassis ground.
  Connector & terminal
  
  (i221) No. 6 (+) - Chassis ground (-):
  
  (i221) No. 14 (+) - Chassis ground (-):
Is the voltage 5 V or less?

Yes : Go to 4.

No : Repair or replace the short circuit to power supply of the harness between the data link connector and central gateway control module.
CHECK FOR SHORT BETWEEN LINES IN HARNESS BETWEEN DATA LINK CONNECTOR AND CENTRAL gateway control module .
1. Turn the ignition switch to OFF.
2. Using the tester, measure the resistance between terminals.
  Connector & terminal
  
  (i221) No. 6 - (i221) No. 14:
Is the resistance 1 MΩ or more?

Yes : Go to 5.

No : Repair or replace the short circuit between lines of the harness between the data link connector and central gateway control module.
CHECK END RESISTANCE .
1. Connect the central gateway control module connector.
2. Using a tester, measure the resistance between terminals of data link connector.
  Connector & terminal
  
  (i221) No. 6 - (i221) No. 14:
Is the resistance 114 - 126 Ω?

Yes : CAN communication circuit is normal.

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