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Transmission control module(TCM)

Transmission control module (TCM)



DRIVE

When the selector lever on a car with automatic transmission is moved to a position other than P or N, battery positive voltage (B+) is applied to pin 86 of the Motronic control module. The control module then opens the idle air control valve slightly more to compensate for the increase in load. Pin 86 is not used on cars equipped with a manual gearbox.

If a gear position other than P or N is selected, the ignition timing will also be temporarily retarded, depending on throttle position, in order to protect the automatic transmission.

Torque reduction

When upshifts or downshifts are performed, the TCM grounds pin 85 of the Motronic control module. Depending on the gear selected and whether upshifting or downshifting is performed, the TCM varies the duration of the grounding signal between 0 and 250 ms.

The Motronic control module retards the ignition on the basis of load and engine rpm so that the ignition timing will be between -10 ° and +30° TDC.

If no signal is received, the result could be "harsher" shifting and shorter transmission life.

CHECK ENGINE request

Should an emission-related fault be detected in the automatic transmission, the TCM will apply a 2 Hz PWM signal to pin 65 of the Motronic control module. The Motronic control module will then cause the CHECK ENGINE lamp (MIL) to light up.



When the ignition switch is turned to the ON position the TCM sends a ground signal for 1 second as a test.