Theory Of Operation

WARNING: This page is about a different variant/trim than selected.

The current regulator in the TCM indicates the following circuit failures to the Central Processing Unit (CPU) using an Application Specific Integrated Circuit (ASIC) via Serial Peripheral Interface (SPI) Bus:

Short to battery
Short to ground or open circuit (can only be distinguished when the output stage is in idle mode, i.e. commanded current is 0 mA)

In addition to the circuit failure information, the TCM monitoring software uses a PWM feedback signal generated by the current regulator in the output stage to identify failures. To perform rationality monitoring of the output stage current, the TCM software calculates the actual current dependent on the PWM feedback signal, the output stage power supply voltage and the actual transmission oil temperature. The TCM can only distinguish between a short to ground and an open circuit failure if the output stage is deactivated. Depending on the required time to bring the transmission into a Limp Home mode, a further evaluation of the failure is determined after switching off the output stage in order to distinguish between both failure types.