DTC U0079
Diagnostic Instructions Perform the Diagnostic System Check prior to using this diagnostic procedure: Diagnostic System Check - Vehicle Review the description of Strategy Based Diagnosis: Strategy Based Diagnosis An overview of each diagnostic category can be found here: Diagnostic Procedure Instructions DTC Descriptor Control Module Communication CAN Bus 4 Off For symptom byte information, refer to Symptom Byte List. Diagnostic Fault Information
| Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
| CAN 4 Serial Data (+) | U0079* | U0100– U02FF, U1100– U12FF, U1600– U17FF, U2200– U23FF, U2400– U25FF* | U0079* | — |
| CAN 4 Serial Data (-) | U0079* | U0100– U02FF, U1100– U12FF, U1600– U17FF, U2200– U23FF, U2400– U25FF* | U0079* | — |
| * Other DTCs may set with this fault. |
Circuit/System Description The devices connected to the CAN 4 serial data circuits (4100 & 4101) monitor for serial data communications during normal vehicle operation. The serial data is transmitted on two twisted wires that allow speeds up to 500 Kbit/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 4 bus during normal vehicle operation. The CAN 4 bus is a differential bus. The CAN 4 serial data (+) and CAN 4 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 4 serial data (+) circuit and subtracts 1 V from the CAN 4 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. Conditions for Running the DTC The system voltage is between 9–16 V. The vehicle power mode requires serial data communications. Conditions for Setting the DTC The device setting the DTC has attempted to establish communications on the CAN 4 serial data circuits more than 3 times. Action Taken When the DTC Sets The device suspends all message transmission. The device uses default values for all parameters received on the serial data circuits. The device inhibits the setting of all other communication DTCs. Conditions for Clearing the DTC A current DTC will clear when the diagnostic runs and passes. A history DTC will clear after 100 consecutive malfunction-free ignition cycles. Reference Information Schematic Reference Data Communication Schematics Control Module References Connector End View Reference Master Electrical Component List Description and Operation Data Link Communications Description and Operation Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs Scan Tool Reference Control Module References for scan tool information Circuit/System Verification
- Ignition ON/Vehicle In Service Mode.
- Verify DTC U0079 is not set. ⇒ If the DTC is set Refer to Scan Tool Does Not Communicate with Device on CAN 4. ⇓ If the DTC is not set
- All OK.