Temperature Sensor Monitoring

Temperature Sensor Monitoring

If the temperature of the Mechatronik unit rises above a pre-determined level the TCM will be shut down. Prior to the TCM shutting down the TCM will log a fault code, during shutdown the transmission will enter ‘mechanical’ limp-home mode. Temperature monitoring is performed by a temperature dependent resistor mounted on the in the TCM.

Transmission oil Temperature Sensor Monitoring

The TCM monitors for faults associated with the transmission oil temperature sensor via open and short circuit fault detection.

The temperature cannot alter by more than a pre-defined differential between any two consecutive measurements. The transmission oil temperature must rise after the engine has been started provided that the oil temperature was low enough to begin with (The vehicle must be driven and the diagnostic test condition met).

Gear Ratio Monitoring

Gear ratio diagnostic checks that each gear ratio is correctly engaged. Also, following a gear shift the diagnostic checks that the transmission has engaged the target gear within the allowed time.

Torque Converter Monitoring

The TCM checks that the torque converter can be locked correctly. If torque converter lock-up does not occur correctly the TCM performs the appropriate fail-safe action of opening the Torque converter clutch.

Plausibility Checking

The TCM detects a fault if an excessive voltage jump is identified between any two consecutive measurements. Also, with the engine started from cold the transmission oil temperature will start to rise. Therefore the Mechatronik unit or transmission oil temperature will also start to rise because the TCM is surrounded by transmission oil. If the engine and output shaft speed is higher than a set threshold for a predetermined length of time without the substrate temperature rising above a set threshold a fault will be detected.

Pressure Regulator/Solenoid Monitoring

Each pressure regulator and solenoid is monitored for open circuits and short circuits. The TCM also checks that the current being delivered to each solenoid valve or pressure regulator is within valid limits. When each solenoid is being driven with minimum current the TCM checks that the current is not above a threshold value. If a solenoid is being driven with maximum current, it checks that the current is not below a valid threshold. If either of these two errors occur a plausibility error is logged and the appropriate fail-safe action is performed.

Output Speed Monitor

It is possible for the TCM to diagnose electrical errors associated with the output speed sensor while the vehicle is stationary as well as moving. Plausibility monitoring is performed on the sensor output when the vehicle is moving.

Input Speed Monitor

It is possible for the TCM to diagnose electrical errors associated with the input shaft speed sensor while the vehicle is stationary as well as moving. Plausibility monitoring is performed on the sensor output when the vehicle is moving.

Position Sensor Monitoring

The TCM can identify position errors with a position switch located within the transmission. If an unrecognized position code is read by the TCM a plausibility fault will be logged.

Torque Converter Lock-up Control

The TCM controls how the torque converter clutch is engaged as a function of the accelerator pedal position, output speed, transmission oil temperature, gear selected and shift program. Lock-up is possible in all forward gears, but usually it is restricted to fourth, fifth and sixth gears. To make use of the comfort enhancing effect of the torque converter, the converter clutch can be disengaged prior to a downshift or up-shift. The torque converter lock up clutch is always modulated to allow for controlled slip, to further improve the shift quality.