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.
Lock-Up-Solenoid, SLU
The lock-up solenoid, SLU is located in the transmission control system, which is fitted on the front edge of the gearbox. The lock-up solenoid, SLU consists of an electrical coil which controls a hydraulic valve. The solenoid is controlled with a pulsed (PWM) voltage and is grounded via the Transmission Control Module (TCM). The solenoid controls torque converter lock-up engagement. The engagement takes place by means of the solenoid being pulsed in, which enables a gentle engagement of the lock-up function. The solenoid permits the torque converter to work in one of three positions: "Open", "Controlled slipping" and "Locked". The hydraulic function of the solenoid is linear.
The solenoid can be diagnosed.
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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.
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