Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P0977: Shift Solenoid "B" Control Circuit High: Notes
1. -
DTC detecting condition:
Immediately at fault recognition
Trouble symptom:
Gear is not changed. (No down-shift)
Wiring diagram:
CVT control system Ref. to WIRING SYSTEM (IMPREZA MODEL)>CVT CONTROL SYSTEM .
- Use CHECK BOARD when measuring the TCM terminal voltage and resistance.
- After servicing or replacing faulty parts, perform the last step of the basic diagnostic procedure. Ref. to TRANSMISSION (DIAGNOSTICS) (IMPREZA MODEL)>BASIC DIAGNOSTIC PROCEDURE .
- CHECK HARNESS
.CAUTION:
Start work after ATF cools down.
- Turn the ignition switch to OFF.
- Disconnect the TCM connector.
- Remove the transmission valve cover.
- Disconnect the control valve body connector.
- 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 Ω?
Yes: Go to 2.
No: Repair the open circuit of harness.
- CHECK HARNESS
.
- Turn the ignition switch to ON.
- Measure the voltage between TCM connector and chassis ground.
Connector & terminal
(T10) No. 30 (+) - Chassis ground (-):
Is the voltage approx. 0 V?
Yes: Go to 3.
No: Repair the short circuit of harness.
- CHECK PRIMARY DOWN SOLENOID
.
- Connect the connector for control valve body.
- Measure the resistance between TCM connector and transmission body.
Connector & terminal
(T10) No. 30 - Transmission body:
Is the resistance approximately 10 - 14.2 Ω? (When cold)
Yes: Check for poor contact of connector, and if no fault is found, replace the TCM. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR580 IMPREZA)>TRANSMISSION CONTROL MODULE (TCM) .
No: Go to 4.
- CHECK HARNESS INSIDE TRANSMISSION
.
Check for the harness pinch, damage.
Is there any fault in the harness?
Yes: Replace the transmission harness.
No: Replace the control valve body. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR580 IMPREZA)>CONTROL VALVE BODY .
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.