Theory Of Operation
Electronic Control Units (ECUs) require the following four components to properly communicate on a Controller Area Network (CAN) data bus:
- Power (Battery/Fused B+/Ignition)
- Ground
- Correct CAN bus voltage
- Correct vehicle configuration
CAN BUS FAULTS
| TYPES OF CAN BUS FAULTS | |
|---|---|
| LOSS OF COMMUNICATION | will set by an active receiving/reporting ECU on a CAN Bus network that detects no communication from another ECU on the same CAN Bus network. Insufficient power, ground, bus voltage, or inaccurate vehicle configuration will cause a loss of communication. |
| IMPLAUSIBLE MESSAGE | will set by an active receiving/reporting ECU, when it determines the data sent from the active transmitting/offending ECU is missing part of the message, or the message is an irrational value over the CAN Bus. |
| MISSING MESSAGE | will set by an active receiving/reporting ECU, when it determines a data message to be missing partial information when sent from the active transmitting/offending ECU over the CAN Bus network. |
| BUS OFF | set by an ECU that has experienced approximately 32 transmit errors, this can be caused by ECU internal faults as well as external bus faults like shorts or plugging and unplugging test tools to the diagnostic connector. |
| PHYSICAL | is only detectable by an ECU that has a transceiver that is able to detect shorts on the bus. If the ECU does not, it generally will set bus off faults due to shorted bus lines. |
Several ECUs on this vehicle are connected to and communicate on multiple CANs. For additional information on the communication network(s), Refer to DESCRIPTION AND OPERATION .