Circuit/System Description

The serial data is transmitted on two twisted wires that allow speeds up to 500 Kb/s. The twisted pair is terminated with two 120 Ω resistors, which can be a separate resistor in a connector assembly or internal to a control module. The resistors are used as the load for the Powertrain high speed GMLAN bus during normal vehicle operation. The Powertrain high speed GMLAN is a differential bus. The Powertrain high speed GMLAN serial data bus (+) and Powertrain high speed GMLAN serial data (-) are driven to opposite extremes from a rest or idle level of approximately 2.5 V. Driving the lines to their extremes, adds 1 V to the Powertrain high speed GMLAN serial data bus (+) circuit and subtracts 1 V from the Powertrain high speed GMLAN serial data bus (-) circuit. If serial data is lost, control modules will set a no communication code against the non-communicating control module. Note that a loss of serial data DTC does not represent a failure of the control module that set it.