Serial Communication

The vehicle system control modules, as well as the TECH 2 diagnostic scan tool, communicate with each other via the serial communication lines using serial data. Serial data transfers information, one bit at a time, over a single line called the data bus. Except for the engine control module (ECM), all control modules communicating on the data bus use universal asynchronous receiver and transmitter (UART) communication. The UART is a 5-volt data line that toggles the voltage to ground (0 volt) at a fixed bit pulse width during communication. The UART transmits data at the rate of 8.2 kilobits per second (8192 bits per second). In UART communications, when there is no communication on the data line, the system voltage is 5 volts.