Honda ACCORD HYBRID 2005 Service Manual page 1762

Multiplex Integrated Control System (MICS)
S y s t e m D e s c r i p t i o n ( c o n t ' d )
Network " L o s s of Communication" Error Checking
The B-CAN and F-CAN systems send messages to each other to check the integrity of the network communication circuit. They do this by
sending a specific digital message out after an event. For example, turning the ignition switch to ON. After the switch to ON, all the ECUs on the
communication circuit expect to receive a message from other specific units within a specified amount of time. If the message is not received,
the ECU will transmit a DTC reporting that the control units did not communicate.
Example of communication circuit test
Normal circuit
1. Ignition switch turned ON.
2. The door multiplex control unit transmits a door switch signal.
3. The multiplex integrated control unit (IV1ICU), relay control module and gauge control module receive the door lock switch signal.
4. Communication circuit test is passed.
Since the door lock switch message was received by all the ECUs expecting to receive a signal, the communication circuit between those units
is OK. There are multiple signal sent and received by each ECU during this time to insure that the communication circuit is intact.
Failed circuit
5. Ignition switch is turned ON.
6. The door multiplex control unit transmits a door switch signal.
7. The multiplex integrated control unit (MICU), relay control 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.
8. Each ECU that expects to receive the door lock switch signal from the door multiplex control unit will transmit DTCs for the signal that it did
not receive.
Door Multiplex
Control Unit
Door Lock
S w i t c h
B-CAN
G a u g e
Control
Module
B-CAN
MICU
K-Line
H D S
B-CAN
Relay
Control
Module
D T C s set for:
• Door lock switch signal not received by M I C U
• Door lock switch signal not received by G a u g e
Control Module
• Door lock switch signal not received by Relay
Control Module
Since there is a break in the communication circuit, the door lock switch signal could not be received by the gauge control module, multiplex
integrated control unit (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. For example, the door multiplex control unit sends keyless panic signal and
door lock switch signal during the communication circuit test.
Diagnostic Trouble Codes
There are three DTC types used by the CAN networks.
Internal error DTCs The ECUs run internal checks. If one finds that there is an internal ECU problem, it will set an internal error DTC.
Confirm that the battery and charging system are OK. If so, this indicates that the ECU needs to be replaced.
Loss of
communication DTCs
Loss of communication DTCs (and Bus-off DTCs) are set when there is a problem with the communication between
ECUs. This could be in the connections, the wiring, or the ECU {as called out in the DTC Troubleshooting).
Signal error DTCs
The ECUs can run diagnostics on some input circuits to determine if that circuits is functioning properly (no opens
or shorts). If a circuit falls the diagnostic test, a DTC will set (NOTE: Not all input circuits are tested for errors).
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