DTC U0077: Lin Communication Bus "ECM/Pcm" Off: Notes

WARNING: This page is about a different variant/trim than selected.

1. -

DTC detecting condition:

Immediately at fault recognition

Wiring diagram:

Engine Electrical System Ref. to WIRING SYSTEM (CROSSTREK MODEL (HEV))>ENGINE ELECTRICAL SYSTEM .

Courtesy of SUBARU OF AMERICA, INC.

CAUTION: Use the check board when measuring the ECM terminal voltage and resistance. Ref. to ENGINE (DIAGNOSTICS) (H4DO (HEV))>GENERAL DESCRIPTION>PREPARATION TOOL>HOW TO USE CHECK BOARD .

NOTE: After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Ref. to ENGINE (DIAGNOSTICS) (H4DO (HEV))>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .

Courtesy of SUBARU OF AMERICA, INC.

CHECK DTC .
Using the Subaru Select Monitor or a general scan tool, read the DTC of [Engine]. Ref. to COMMON (DIAG)>DIAGNOSTIC TROUBLE CODE (DTC) .

Is DTC U0077 displayed? (Current malfunction)

Yes : Go to 2.

No : Even if DTC is detected, the circuit has returned to a normal condition at this time. Reproduce the failure, and then perform the diagnosis again. Using the Subaru Select Monitor or a general scan tool, perform the clear memory. Ref. to COMMON (DIAG)>CLEAR MEMORY .
CHECK WIRING HARNESS BETWEEN ECM AND ACTIVE GRILLE SHUTTER (OPEN) .
1. Turn the ignition switch to OFF.
2. Disconnect the connector from ECM.
3. Disconnect the connector from the active grille shutter.
4. Measure the resistance of harness between ECM connector and active grille shutter connector.
  Connector & terminal
  
  (B134) No. 17 - (B63) No. 3:
Is the resistance less than 1 Ω?

Yes : Go to 3.

No : Repair the open circuit in harness between ECM connector and active grille shutter connector.
CHECK WIRING HARNESS BETWEEN ECM AND ACTIVE GRILLE SHUTTER (SHORT TO GROUND) .
Measure the resistance between the ECM connector and engine ground.

Connector & terminal

(B134) No. 17 - Engine ground:

Is the resistance 1 MΩ or more?

Yes : Go to 4.

No : Repair the short circuit to ground in harness between ECM connector and active grille shutter connector.
CHECK WIRING HARNESS BETWEEN ECM AND ACTIVE GRILLE SHUTTER (SHORT TO POWER SUPPLY) .
1. Turn the ignition switch to ON.
2. Measure the voltage between ECM connector and engine ground.
  Connector & terminal
  
  (B134) No. 17 (+) - Engine ground (-):
Is the voltage less than 1 V?

Yes : Go to 5.

No : Repair the short circuit to power supply in harness between ECM connector and active grille shutter connector.
CHECK DTC .
1. Turn the ignition switch to OFF.
2. Connect the connector to the active grille shutter.
3. Connect the connector to ECM.
4. Using the Subaru Select Monitor or a general scan tool, perform the clear memory of [Engine]. Ref. to COMMON (DIAG)>CLEAR MEMORY .
5. Using the Subaru Select Monitor or a general scan tool, read the DTC of [Engine]. Ref. to COMMON (DIAG)>DIAGNOSTIC TROUBLE CODE (DTC) .
Is DTC U0077 displayed? (Current malfunction)

Yes : Replace the ECM. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO (HEV))>ENGINE CONTROL MODULE (ECM) .

No : Even if DTC is detected, the circuit has returned to a normal condition at this time. Reproduce the failure, and then perform the diagnosis again.

NOTE: In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause. Using the Subaru Select Monitor or a general scan tool, perform the clear memory. Ref. to COMMON (DIAG)>CLEAR MEMORY .