DTC P1758: Cold Start Torque Converter Clutch Pressure Control Solenoid Control Circuit Stuck On: Notes

WARNING: This page is about a different car, the 2022 Subaru WRX. However, it is still accessible from the selected car via links, so may be relevant.

1. -

DTC detecting condition:

Detected when two consecutive driving cycles with fault occur.

Trouble symptom:

Engine stalls at deceleration.

Wiring diagram:

CVT control system Ref. to WIRING SYSTEM>CVT CONTROL SYSTEM>WIRING DIAGRAM

Courtesy of SUBARU OF AMERICA, INC.

CAUTION:

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)>BASIC DIAGNOSTIC PROCEDURE

CHECK DTC .
Read the DTC of [Transmission] using the Subaru Select Monitor. Ref. to TRANSMISSION (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC)

Is only DTC P1758 displayed?

Yes : Go to 4.

No : Go to 2.
CHECK DTC .
Read the DTC of [Transmission] using the Subaru Select Monitor. Ref. to TRANSMISSION (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC)

Is DTC P2758 displayed?

Yes : Perform the diagnosis according to DTC P2758. Ref. to TRANSMISSION (DIAGNOSTICS)>DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)>DTC P2758 TORQUE CONVERTER CLUTCH PRESSURE CONTROL SOLENOID CONTROL CIRCUIT STUCK ON

No : Go to 3.
CHECK DTC .
Read the DTC of [Transmission] using the Subaru Select Monitor. Ref. to TRANSMISSION (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC)

Is DTC P2763 or P2764 displayed?

Yes : Perform the diagnosis according to DTC P2763 or P2764. Ref. to TRANSMISSION (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC)>LIST

No : Go to 4.
CHECK LOCK-UP DUTY SOLENOID (ACTIVE TEST) .
1. Turn the ignition switch to ON.
2. Using the Subaru Select Monitor, perform the active test of the lock-up duty solenoid. Ref. to TRANSMISSION (DIAGNOSTICS)>ACTIVE TEST
Does the indication of 0 → 50% appear repeatedly during the active test, and does operating sound emit during indicating 50%?

Yes : Go to 8.

No : Go to 5.
CHECK LOCK-UP DUTY SOLENOID .
1. Turn the ignition switch to OFF.
2. Disconnect the transmission connector.
3. Measure the resistance between transmission connector and transmission body.
  Connector & terminal
  
  (T1) No. 8 - Transmission body:
Is the resistance approximately 10 - 14.2 Ω? (When cold)

Yes : Replace the control valve body. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>CONTROL VALVE BODY

No : Go to 6.
CHECK HARNESS .
CAUTION:
Start work after ATF cools down.
1. Remove the transmission oil pan.
2. Disconnect the control valve body connector.
3. Measure the resistance between transmission connector and control valve body connector.
  Connector & terminal
  
  (T1) No. 8 - (T11) No. 2:
Is the resistance less than 1 Ω?

Yes : Go to 7.

No : Repair the open circuit of harness.
CHECK HARNESS .
Measure the resistance between transmission connector and control valve body.

Connector & terminal

(T11) No. 2 - Control valve body:

Is the resistance 1 MΩ or more?

Yes : Replace the control valve body. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>CONTROL VALVE BODY

No : Repair the short circuit of harness.
CHECK TRANSMISSION FLUID .
1. Connect all connectors.
2. Check the amount of ATF. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>CVTF>INSPECTION
Is the check result OK?

Yes : Go to 9.

No : Adjust the amount of ATF. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>CVTF>INSPECTION Go to 9.
CHECK TRANSMISSION FLUID .
Check the condition of ATF. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>CVTF>REPLACEMENT

Is the check result OK?

Yes : Return ATF. Go to 10.

No : Follow the "Corrective action" of ATF (CVTF) "CONDITION CHECK". Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>CVTF>REPLACEMENT Go to 10.
CHECK ENGAGEMENT CONDITION OF LOCK-UP CLUTCH .
1. Start the engine.
2. Warm up until the ATF temperature exceeds 50°C (122°F).
3. Depress the brake pedal, and shift the select lever to "D" range.
Are there any vibrations due to engine stall or engine speed drop?

Yes : Replace the control valve body. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>CONTROL VALVE BODY Go to 12.

No : Go to 11.
CHECK INPUT SIGNAL FOR TCM .
1. Lift up the vehicle.
2. Start the engine.
3. Warm up until the ATF temperature reaches to 40 - 70°C (104 - 158°F).
4. Depress the brake pedal, and shift the select lever to "D" range.
5. Drive at 2 km/h (1 MPH) or more.
6. Shift the select lever to "P" range.
7. Stabilize the engine speed at idle.
8. Using the Subaru Select Monitor, read data of [Actual line press.] in the [Data Monitor] of [Transmission]. Ref. to TRANSMISSION (DIAGNOSTICS)>DATA MONITOR
Is [Actual line press.] 0.5 - 1.5 MPa?

Yes : Replace the control valve body. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>CONTROL VALVE BODY Go to 12.

No : Perform the diagnosis according to DTC P0867. Ref. to TRANSMISSION (DIAGNOSTICS)>DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)>DTC P0867 TRANSMISSION FLUID PRESSURE
DRIVING CHECK FOR LOCK-UP CONDITION .
1. Using the Subaru Select Monitor, perform the clear memory of [Transmission]. Ref. to COMMON (DIAGNOSTICS)>CLEAR MEMORY
2. Turn the ignition switch to OFF.
3. Soak until the engine coolant temperature drops below 30°C (86°F).
4. Start the engine.
5. Depress the brake pedal, and shift the select lever to "D" range.
6. Shift the select lever to "P" range.
7. Turn the ignition switch to OFF.
8. Start the engine.
9. Perform step 3 - step 6 again.
10. Read the DTC of [Transmission] using the Subaru Select Monitor. Ref. to TRANSMISSION (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC)
Does the AT OIL TEMP light blink and is DTC P2758 displayed? Or are there any vibrations due to engine stall or engine speed drop?

Yes : Replace the torque converter assembly, and perform step 12 again. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>TORQUE CONVERTER If the replacement of the torque converter assembly does not eliminate the malfunction, replace the transmission assembly and perform step 12 again. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>TRANSMISSION ASSEMBLY

No : Go to 13.
DRIVING CHECK FOR LOCK-UP CONDITION .
1. Using the Subaru Select Monitor, perform the clear memory of [Transmission]. Ref. to COMMON (DIAGNOSTICS)>CLEAR MEMORY
2. Turn the ignition switch to OFF.
3. Soak until the engine coolant temperature drops below 30°C (86°F).
4. Start the engine.
5. Using Subaru Select Monitor, display data of [Accel. Opening Angle] in [Data Monitor] of [Transmission]. Ref. to TRANSMISSION (DIAGNOSTICS)>DATA MONITOR
6. Depress the brake pedal, and shift the select lever to "D" range.
7. With the engine coolant temperature below 54°C (129°F), perform five-second acceleration with [Accel. Opening Angle] at approximately 30% three times.
8. Shift the select lever to "P" range.
9. Turn the ignition switch to OFF.
10. Start the engine.
11. Perform step 3 - step 8 again.
12. Read the DTC of [Transmission] using the Subaru Select Monitor. Ref. to TRANSMISSION (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC)
Does the AT OIL TEMP light blink and is DTC P1758 displayed? Or are there any vibrations due to engine stall or engine speed drop?

Yes : Replace the torque converter assembly, and perform step 13 again. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>TORQUE CONVERTER If the replacement of the torque converter assembly does not eliminate the malfunction, replace the transmission assembly and perform step 13 again. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>TRANSMISSION ASSEMBLY

No : Current condition is normal. It is possible that temporary failure occurred to the energization status or to the hydraulic circuit.