Class 2 Serial Data

The Class 2 serial data circuit allows the control modules to communicate with each other. The modules send a series of digital signals pulsed from high to low voltage (approximately 7 volts to 0 volts). These signals are sent in variable pulse widths of one or two bits. A string of these bits creates a message that is sent in a prioritized data packet. This allows more than one module to send messages at the same time without overloading the serial data line. The speed, or BAUD rate, at which the control modules communicate depends on the message content. Large message content lowers the BAUD rate while small message content increases the BAUD rate. The average BAUD rate is approximately 10.4 Kbps (10,400 bits per second).

When the key is ON, each module sends a State of Health message to the other control modules using the class 2 serial data line. This ensures that the modules are working properly. When the module stops communicating, a loss of the state of health message occurs. The control modules that expect to receive the message detect the loss, and will set a loss of the state of health diagnostic trouble code (DTC).