Subaru Legacy BN/BS (2015-2019) Service Manual: Dtc p0977 shift solenoid "b" control circuit high

Subaru Legacy BN/BS (2015-2019) Service Manual / Continuously variable transmission (diagnostics) / Diagnostic procedure with diagnostic trouble code (dtc) / Dtc p0977 shift solenoid "b" control circuit high

DTC DETECTING CONDITION:

Immediately at fault recognition

TROUBLE SYMPTOM:

Gear is not changed. (No down-shift)

1. ENGINE TYPE FB

WIRING DIAGRAM:

CVT control system CVT Control System > WIRING DIAGRAM

STEP	CHECK	YES	NO
1.CHECK HARNESS. CAUTION: Start work after ATF cools down. 1) Turn the ignition switch to OFF. 2) Disconnect the TCM connector. 3) Remove the transmission valve cover. 4) Disconnect the control valve body connector. 5) Measure the resistance between TCM connector and control valve body connector. Connector & terminal (T10) No. 30 — (T11) No. 7:	Is the resistance less than 1 --	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0977 SHIFT SOLENOID "B" CONTROL CIRCUIT HIGH	Repair the open circuit of harness.
2.CHECK HARNESS. 1) Turn the ignition switch to ON. 2) Measure the voltage between TCM connector and chassis ground. Connector & terminal (T10) No. 30 (+) — Chassis ground (−):	Is the voltage approx. 0 V-	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0977 SHIFT SOLENOID "B" CONTROL CIRCUIT HIGH	Repair the short circuit of harness.
3.CHECK PRIMARY DOWN SOLENOID. 1) Connect the connector for control valve body. 2) Measure the resistance between TCM connector and transmission body. Connector & terminal (T10) No. 30 — Transmission body:	Is the resistance approx. 10 — 13.5 -- (when cold)	Check for poor contact of connector, and if no fault is found, replace the TCM. Transmission Control Module (TCM)	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0977 SHIFT SOLENOID "B" CONTROL CIRCUIT HIGH
4.CHECK HARNESS INSIDE TRANSMISSION. Check for the harness pinch, damage.	Is there any fault in the harness-	Replace the transmission harness.	Replace the control valve body. Control Valve Body

2. ENGINE TYPE EZ

WIRING DIAGRAM:

CVT control system CVT Control System > WIRING DIAGRAM

STEP	CHECK	YES	NO
1.CHECK HARNESS. 1) Turn the ignition switch to OFF. 2) Disconnect the TCM and transmission connectors. 3) Measure the resistance between TCM connector and transmission connectors. Connector & terminal (B54) No. 30 — (B22) No. 1:	Is the resistance less than 1 --	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0977 SHIFT SOLENOID "B" CONTROL CIRCUIT HIGH	Repair the open circuit of harness.
2.CHECK HARNESS. 1) Turn the ignition switch to ON. 2) Measure the voltage between TCM connector and chassis ground. Connector & terminal (B54) No. 30 (+) — Chassis ground (−):	Is the voltage approx. 0 V-	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0977 SHIFT SOLENOID "B" CONTROL CIRCUIT HIGH	Repair the short circuit of harness.
3.CHECK PRIMARY DOWN SOLENOID. Measure the resistance between transmission connector and transmission body. Connector & terminal (T4) No. 1 — Transmission body:	Is the resistance approx. 10 — 13.5 -- (when cold)	Check for poor contact of connector, and if no fault is found, replace the TCM. Transmission Control Module (TCM)	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0977 SHIFT SOLENOID "B" CONTROL CIRCUIT HIGH
4.CHECK HARNESS INSIDE TRANSMISSION. CAUTION: Start work after ATF cools down. 1) Remove the transmission oil pan. 2) Check for the harness pinch, damage.	Is there any fault in the harness-	Replace the transmission harness.	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0977 SHIFT SOLENOID "B" CONTROL CIRCUIT HIGH
5.CHECK HARNESS INSIDE TRANSMISSION. 1) Disconnect the control valve body connector. 2) Turn the ignition switch to ON. 3) Measure the voltage between transmission connector and transmission body. Connector & terminal (T4) No. 1 (+) — Transmission body (−):	Is the voltage approx. 0 V-	Replace the control valve body. Control Valve Body	Replace the transmission harness.

3. OUTLINE OF DIAGNOSIS

• Detect short circuit to power supply or open circuit of the shift-down fluid pressure control solenoid drive circuit.

• Judge as NG if an open circuit or a power-supply short circuit is detected more than 10 times in the shift-down fluid pressure control solenoid drive circuit.

4. EXECUTION CONDITION

Secondary Parameters	Execution condition
12 V battery system voltage	≥ 9 V
Commanded duty of shift down pressure control solenoid	0%

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
Signal of malfunction from solenoid driver IC	ON
As defined by:
Measured shift down pressure control solenoid voltage ≥ 2.5 V

Time Needed for Diagnosis: 0.2 seconds

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

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