Information Bus: Description and Operation

Data Link Communications Description and Operation

Circuit Description
The vehicle system control modules, as well as the diagnostic scan tool, communicate with each other via the data bus. Apart from the powertrain control module (PCM), the control modules communicating on the data bus use UART communication.

UART is a 5-volt data bus that toggles the voltage to ground (0 volt) at a fixed-bit pulse width and transmits data at 8.2 kilobits per second. When there is no communication on the UART data bus, the system voltage is +5 volts with respect to battery ground.

The PCM uses class 2 communication. This toggles the data bus from 0-7 volts with either a short or long pulse width at an average rate of 10.4 kilobits per second. When there is no communication on the class 2 data bus, the system voltage is 0 volt.

The powertrain interface module (PIM) converts class 2 communication into UART and UART into class 2. The scan tool is able to communicate with both UART and class 2 control modules.