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Home >> Cadillac >> 2021 >> CT4 Sport, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 191 (Data Communications - Diagnostic Information And Procedures (3 Of 3)) >> Diagnostic Information and Procedures >> Scan Tool Does Not Communicate with Device on CAN 8 >> Circuit/System Description

Circuit/System Description

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The devices connected to the CAN 8 serial data circuits (4104 & 4105) monitor for serial data communications during normal vehicle operation. The serial data is transmitted on two twisted wires that allow speeds up to 2 Mbit/s. The twisted pair is terminated with two 120 Ω resistors. Each terminating resistor can be a separate resistor in a connector assembly or internal to a device. The resistors are used as the load for the CAN 8 bus during normal vehicle operation. The CAN 8 bus is a differential bus. The CAN 8 serial data [+] and CAN 8 serial data [-] circuits 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 CAN 8 serial data [+] circuit and subtracts 1 V from the CAN 8 serial data [-] circuit. If serial data is lost, devices will set a no communication code against the non-communicating device. Note that a loss of serial data DTC does not represent a failure of the device that set it.

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