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: General
TG 81SC is an 8 speed electronically controlled automatic transmission with a lock-up function for the seven highest gears. The Transmission Control Module (TCM) adapts the gear changes to ensure that the correct gear is selected for the driving mode, engine load, driver requirements, speed etc. This gives good fuel economy combined with increased comfort by ensuring smoother gear changes and lower noise levels.
The Transmission Control Module (TCM) receives information on required gear position and required driving style (driving program) from the driver. Together with signals from a number of sensors in the transmission and the engine management system, this enables the calculation of optimum gearshift timing and lock-up engagement, in contrast to a gearbox with only a hydraulic control system. The control module takes consideration of small changes in operating conditions and adapts the different transmission functions so that the correct gear is always selected in accordance with the driving program selected by the driver.
The Transmission Control Module (TCM) has an adaptive capacity intended to ensure even gearshift quality during the whole service life of the transmission.
In order to be able to determine gearshift timing and lock-up engagement precisely, based on the selected driving program, the control module receives information on the following:
- Selected gear position - from the gear position sensor.
- Speed of transmission input shaft - from transmission speed sensor, input shaft.
- Speed of transmission output shaft - from transmission speed sensor, output shaft.
- Transmission oil temperature - from temperature sensor in the transmission.
- Engine speed and torque, and throttle opening - from Engine Control Module (ECM) via the CAN.
- Whether and how much the accelerator pedal is depressed - from Engine Control Module (ECM) via CAN.
- Engine temperature - from Engine Control Module (ECM) via CAN.
- Vehicle speed - from Brake Control Module (BCM) via CAN.
- Whether and how much the brake pedal is depressed - from Brake Control Module (BCM) via CAN.
- Vehicle's lateral acceleration - from Brake Control Module (BCM) via CAN.
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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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