Theory Of Operation

The purpose of the diagnostic is to detect circuit failures on any of the output stages. All output stages are controlled by a current controller that Controller Area Network (CAN) operate an output stage in two different modes:

• Current controlled mode (pressure regulators)
• Switched mode or Pulse Width Modulated (PWM) controlled (solenoids)

Pressure Regulator Monitoring:  The current regulator Application-Specific Integrated Circuit (ASIC) in the Transmission Control Module (TCM) indicates the following circuit failures via Serial Peripheral Interface (SPI) bus to the Central Processing Unit (CPU):

• Short to ground
• Short to battery or open circuit

Solenoid Monitoring:  The TCM measures the actual solenoid voltages and compares them to calibrated thresholds to identify the following electrical failures:

• Short to ground or open circuit
• Short to battery