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.
System Overview: Components
The following components are included in the control system for automatic transmissions:
- Transmission control module (TCM) - Controls activation and deactivation of the solenoids by processing the signals from components such as the transmission input and output speed sensors and the temperature sensor. Also stores adaptive data as well as diagnostic trouble codes (DTCs) and frozen values for diagnostics
- Shift solenoid, S1 - Controls shifting in the transmission
- Shift solenoid, S2 - Controls shifting in the transmission
- Shift solenoid, S3 - Controls shifting in the transmission
- Shift solenoid, S4 - Controls shifting in the transmission
- Shift solenoid, S5 - Controls shifting in the transmission
- Lock-up solenoid, SLU - Controls the lock-up function and is also used for certain shifts
- Line pressure solenoid, SLT - Controls the transmission line pressure and neutral control
- Line pressure solenoid, SLS - Controls the transmission shifting pressure and is activated for certain gears
- Transmission input speed sensor (input shaft speed) (1) - Provides the transmission control module (TCM) with information about the input shaft speed from the engine
- Speed sensor (output shaft speed) (2) - Provides the transmission control module (TCM) with information about the output shaft speed from the transmission
- Oil temperature sensor (3) - Provides the transmission control module (TCM) with information about the oil temperature of the transmission
- Gear-shift position sensor (4) - Provides the transmission control module (TCM) with information about the selected gear position
- Gear selector module (GSM) - Provides the transmission control module (TCM) with information about the Geartronic mode and winter mode (W) amongst others.
Use the Manual With the Right Hardware
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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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