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 can operate an output stage in two different modes:

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

Pressure Regulator Monitoring:  The current regulator ASIC in the TCM indicates the following circuit failures via SPI bus to the 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