Network ‘‘Loss of Communication'' Error Checking
The B-CAN and F-CAN systems use messages to check the integrity of the network communication circuit by sending a specific message out after a specific event, such as when the ignition switch is turned to ON. After the event occurs all the ECUs on the communication circuit expect to receive a message from a specific unit within a specified amount of time. If the message is not received, the ECU will transmit a DTC reporting that it did not receive the message.
Example of communication circuit test
Normal circuit

1. Ignition switch is turned ON.

1. The Door Multiplex Control Unit transmits a door switch message.

1. The MICU, Relay Module and Gauge Control Module receive the door lock switch signal.

1. Communication circuit test is passed.

Since the door lock switch message was received by all the ECUs expecting to receive a message, the communication circuit between those units is judged as OK. There are multiple messages sent and received by each ECU during this time to insure that the entire circuit is intact.
Failed circuit

1. Ignition switch is turned ON.

1. The Door Multiplex Control Unit transmits a door switch message.

1. The MICU, Relay Module and Gauge Control Module expect to receive the door lock switch signal, but since there is a break in the communication circuits, it is not received.

1. Each ECU that expects to receive the door lock switch signal from the Door Multiplex Control Unit will transmit DTC data for the message that it did not receive.

Since there is a break in the communication circuit, the door lock switch message could not be received by the gauge control module, MICU or the relay control module. Each of these units will set ‘‘loss of communication'' error codes for the signal(s) they did not receive. There may be multiple communication DTCs if the unit that has become disconnected from the network would normally transmit multiple messages during the communication line test. (Door Multiplex sends Keyless Panic Message and Door Lock Switch Message during the communication circuit test).