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.
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HOMESERVICE MANUALSSUBARU2008FORESTER F4-2.5L DOHC TURBOREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTTRANSMISSION CONTROL SYSTEMSDESCRIPTION AND OPERATIONAUTOMATIC TRANSMISSION (4 AT)LOCKUP CONTROL
2008 Subaru Forester F4-2.5L DOHC Turbo
Lockup Control
2008 Subaru Forester F4-2.5L DOHC TurboSECTION Lockup Control
LOCKUP CONTROL
- The TCM has pre-programmed lockup clutch engagement and disengagement conditions for each gear and shift pattern.The engagement and disengagement conditions are defined in terms of the accelerator pedal position and vehicle speed.
- The TCM controls lockup clutch operation through duty solenoids.
NON-LOCKUP OPERATION
The duty solenoid allows the pilot pressure to be applied to the disengaging end of the valve in the control valve body. The valve then opens the clutch disengaging circuit port to add the lockup operating pressure (torque converter clutch regulating pressure) to the disengaging circuit. Moreover, the valve opens the lockup clutch engaging circuit port and allows the hydraulic fluid in the circuit to flow to the ATF cooler, thus lowering the pressure in the circuit. As a result, the lockup clutch is disengaged due to difference in pressure between both circuits.
This control is performed in all gear positions.
LOCKUP OPERATION
The duty solenoid allows the pilot pressure to be applied to the engaging end of the valve in the control valve body. The valve then opens the clutch engaging circuit port that communicates to the torque converters impeller chamber, allowing high pressure fluid to flow to the lockup clutch. The clutch then engages.
- The TCM controls the current to the duty solenoid by gradually changing the current.As a result, the valve also moves gradually, so the clutch engagement pressure increases smoothly. This causes the lockup clutch to become initially in a half-engaged state and then in a fully engaged state, thus preventing shock during engagement.
This control is performed in all gear positions.
- The TCM has pre-programmed lockup clutch engagement and disengagement conditions for each gear and shift pattern.The engagement and disengagement conditions are defined in terms of the accelerator pedal position and vehicle speed.
- The TCM controls lockup clutch operation through duty solenoids.
NON-LOCKUP OPERATION
The duty solenoid allows the pilot pressure to be applied to the disengaging end of the valve in the control valve body. The valve then opens the clutch disengaging circuit port to add the lockup operating pressure (torque converter clutch regulating pressure) to the disengaging circuit. Moreover, the valve opens the lockup clutch engaging circuit port and allows the hydraulic fluid in the circuit to flow to the ATF cooler, thus lowering the pressure in the circuit. As a result, the lockup clutch is disengaged due to difference in pressure between both circuits.
This control is performed in all gear positions.
LOCKUP OPERATION
The duty solenoid allows the pilot pressure to be applied to the engaging end of the valve in the control valve body. The valve then opens the clutch engaging circuit port that communicates to the torque converters impeller chamber, allowing high pressure fluid to flow to the lockup clutch. The clutch then engages.
- The TCM controls the current to the duty solenoid by gradually changing the current.As a result, the valve also moves gradually, so the clutch engagement pressure increases smoothly. This causes the lockup clutch to become initially in a half-engaged state and then in a fully engaged state, thus preventing shock during engagement.
This control is performed in all gear positions.
RENDER: 1.0x
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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.