CAN Communication Circuit Check: Procedure: Main-Can

Trouble causes:

MAIN-CAN communication circuit is shorted to ground.
MAIN-CAN communication circuit is shorted to power supply.
MAIN-CAN communication circuit is shorted between lines.

Wiring diagram:

CAN communication system Ref. to WIRING SYSTEM>CAN Communication System>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

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, trunk, and rear gate 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.
When the bus line is measured, combined resistance of the end resistance (120 Ω) in ECM and the end resistance (120 Ω) in body integrated unit can be measured. The combined resistance is more than 52 Ω and less than 62 Ω with the stabilizing circuit included. If the measured resistance value becomes 52 Ω or less, main wiring harness or related lines may be shorted. Or, the combined resistance may have changed because of a resistance other than the end resistance created on the circuit. If the measured value is 62 Ω or more, there may be a malfunction such as open circuit in one of the end resistances, in the stabilizing circuit, or in the main wiring harness.
Also, even when the resistance value falls more than 52 Ω and less than 62 Ω, related lines may be open if an error of communication for initializing or a CAN system U-code has occurred. (The resistance cannot be more than 52 Ω and less than 62 Ω if the main wiring harness is open.)

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 MAIN-CAN COMMUNICATION CIRCUIT .
1. Turn the ignition switch to OFF.
2. Disconnect the steering angle sensor connector.
3. Use a tester to measure the resistance between the steering angle sensor connector and chassis ground.
  Connector & terminal
  
  (i74) No. 2 - Chassis ground:
  
  (i74) No. 3 - Chassis ground:
  
  Is the resistance less than 10 Ω?
  
  Yes : Check for ground short. Ref. to LAN SYSTEM (DIAGNOSTICS)>CAN Communication Circuit Check>INSPECTION>GROUND SHORT INSPECTION .
  
  No : Go to 3.
CHECK FOR SHORT TO POWER SUPPLY IN MAIN-CAN COMMUNICATION CIRCUIT .
1. Turn the ignition switch to ON.
2. Use a tester to measure the voltage between the steering angle sensor connector and chassis ground.
  Connector & terminal
  
  (i74) No. 2 (+) - Chassis ground (-):
  
  (i74) No. 3 (+) - Chassis ground (-):
  
  Is the voltage 5 V or less?
  
  Yes : Go to 4.
  
  No : Check for power supply short. Ref. to LAN SYSTEM (DIAGNOSTICS)>CAN Communication Circuit Check>INSPECTION>CHECK POWER SUPPLY SHORT .
CHECK FOR SHORT IN MAIN-CAN COMMUNICATION CIRCUIT .
1. Turn the ignition switch to OFF.
2. Using a tester, measure the resistance between terminals of steering angle sensor connect
  Connector & terminal
  
  (i74) No. 2 - (i74) No. 3:
  
  Is the resistance 52 Ω or less?
  
  Yes : Perform the inspection for resistance of 52 Ω or less. Ref. to LAN SYSTEM (DIAGNOSTICS)>CAN Communication Circuit Check>INSPECTION>52 Ω OR LESS .
  
  No : Go to 5.
CHECK FOR OPEN CIRCUIT IN MAIN-CAN COMMUNICATION CIRCUIT .
Using a tester, measure the resistance between terminals of steering angle sensor connector.

Connector & terminal

(i74) No. 2 - (i74) No. 3:

Is the resistance 62 Ω or more?

Yes : Perform the inspection for resistance of 62 Ω or more. Ref. to LAN SYSTEM (DIAGNOSTICS)>CAN Communication Circuit Check>INSPECTION>62 Ω OR MORE .

No : If the display of CAN system U-code disappears from the current malfunction, the CAN network is currently normal. If the U-code has detected as current malfunction, related lines may be open. Perform the inspection for the related line corresponding to the detected DTC. Ref. to LAN SYSTEM (DIAGNOSTICS)>CAN Communication Circuit Check>LIST .