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Subaru Legacy Service Manual: Dtc u0077 lin communication bus "ecm/pcm" off

DTC DETECTING CONDITION:

Immediately at fault recognition

CAUTION:

After servicing or replacing faulty parts, perform Clear Memory Mode Clear Memory Mode > OPERATION, and Inspection Mode Inspection Mode > PROCEDURE.

WIRING DIAGRAM:

Engine Electrical System ENGINE TYPE FB (WITHOUT PUSH BUTTON START) Engine Electrical System > WIRING DIAGRAM

Engine Electrical System ENGINE TYPE FB (WITH PUSH BUTTON START) Engine Electrical System > WIRING DIAGRAM

STEPCHECKYESNO

1.CHECK DTC.

Check for DTC.

NOTE:

Subaru Select Monitor

Refer to “Read Diagnostic Trouble Code (DTC)” for detailed operation procedure. Read Diagnostic Trouble Code (DTC)

General scan tool

For detailed operation procedures, refer to the general scan tool operation manual.

Is U0077 displayed in «Present fault»-

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC U0077 LIN COMMUNICATION BUS "ECM/PCM" OFF

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. Clear the memory using the Subaru Select Monitor or general scan tool.

NOTE:

Subaru Select Monitor

For detailed procedures, refer to “Clear Memory Mode”. Clear Memory Mode

General scan tool

For detailed operation procedures, refer to the general scan tool operation manual.

2.CHECK BETWEEN ECM CONNECTOR AND BATTERY SENSOR CONNECTOR, AND BETWEEN ECM CONNECTOR AND ACTIVE GRILLE SHUTTER CONNECTOR.

1) Turn the ignition switch to OFF.

2) Disconnect the connectors from ECM, battery sensor and active grille shutter.

3) Measure the resistance of terminals between ECM connector and battery sensor connector, as well as ECM connector and active grille shutter connector.

Connector & terminal

(B134) No. 55 — (B78) No. 2:

(B134) No. 55 — (B63) No. 3:

Is the resistance less than 1 --

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC U0077 LIN COMMUNICATION BUS "ECM/PCM" OFF

Repair the harness and connector.

NOTE:

In this case, repair the following item:

Open circuit of harness between ECM connector and battery sensor connector, and between ECM connector and active grille shutter connector

Poor contact of coupling connector

3.CHECK WIRING HARNESS BETWEEN ECM CONNECTOR AND BATTERY SENSOR CONNECTOR, AND BETWEEN ECM CONNECTOR AND ACTIVE GRILLE SHUTTER CONNECTOR.

Measure the resistance between ECM connector and chassis ground.

Connector & terminal

(B134) No. 55 — Chassis ground:

Is the resistance 1 M- or more-

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC U0077 LIN COMMUNICATION BUS "ECM/PCM" OFF

Repair the short circuit to ground in harness between ECM connector and battery sensor connector, as well as ECM connector and active grille shutter connector.

4.CHECK WIRING HARNESS BETWEEN ECM CONNECTOR AND BATTERY SENSOR CONNECTOR, AND BETWEEN ECM CONNECTOR AND ACTIVE GRILLE SHUTTER CONNECTOR.

1) Turn the ignition switch to ON.

2) Measure the voltage between ECM connector and chassis ground.

Connector & terminal

(B134) No. 55 — Chassis ground:

Is the voltage less than 1 V-

Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC U0077 LIN COMMUNICATION BUS "ECM/PCM" OFF

Repair the short circuit to ground in harness between ECM connector and battery sensor connector, as well as ECM connector and active grille shutter connector.

5.CHECK DTC.

1) Turn the ignition switch to OFF.

2) Connect the battery sensor connector and ECM connector.

3) Clear the memory using the Subaru Select Monitor or general scan tool. Clear Memory Mode > OPERATION

4) Check for DTC.

NOTE:

Subaru Select Monitor

Refer to “Read Diagnostic Trouble Code (DTC)” for detailed operation procedure. Read Diagnostic Trouble Code (DTC)

General scan tool

For detailed operation procedures, refer to the general scan tool operation manual.

Is U0077 displayed in «Present fault»-

Replace the ECM. Engine Control Module (ECM)

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. Clear the memory using the Subaru Select Monitor or general scan tool.

Subaru Select Monitor

For detailed procedures, refer to “Clear Memory Mode”. Clear Memory Mode

General scan tool

For detailed operation procedures, refer to the general scan tool operation manual.

1. OUTLINE OF DIAGNOSIS

Detect malfunction of LIN communication.

Judge as NG when the data sent/received via LIN communication is abnormal.

2. COMPONENT DESCRIPTION

LIN communication is used to send/receive data between ECM, battery sensor and active grille shutter.

3. EXECUTION CONDITION

Secondary Parameters

Execution condition

Battery voltage

≥ 10.9 V

4. GENERAL DRIVING CYCLE

Always perform the diagnosis continuously.

5. DIAGNOSTIC METHOD

If the duration of time while the following conditions are met is longer than the time indicated, judge as NG.

Judgment Value

Malfunction Criteria

Threshold Value

Data sent/received with control modules connected to LIN

No change

or

Checksum error

Time Needed for Diagnosis: 1280 ms

Malfunction Indicator Light Illumination: Illuminates as soon as a malfunction occurs.

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Other materials:

Inspection
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