Mitsubishi Motors Service Manual

2018 / ECLIPSE CROSS / EC - Workshop Manual

54 -CHASSIS ELECTRICAL > 54C-CONTROLLER AREA NETWORK (CAN) > EXPLANATION ABOUT THE M.U.T.-III CAN BUS DIAGNOSTICS

EXPLANATION ABOUT THE M.U.T.-IIISE CAN BUS DIAGNOSTICS

The CAN bus is diagnosed by using "Read all DTCs" function on the M.U.T.-IIISE. "Read all DTCs" automatically reads the diagnosis code from all the ECUs selected in the system list, and displays the diagnostic results in the result field on the left side of the screen and the status of the diagnosis code on the right side of the screen as the respective results. In the CAN bus diagnostics using "Read all DTCs" of M.U.T.-IIISE, it is judged whether there is an abnormality in the CAN bus line based on the diagnostic results displayed in the result field on the left side of the screen.

Screen image of M.U.T.-IIISE (Read all DTCs)	Result field (Left side of the screen)	Action
	"OK" or "-" is displayed for all the systems.	Perform normal failure phenomenon diagnosis.
	"TC" is displayed for one or more systems and "NC" is not displayed at all.	After reading the diagnosis code, pinpoint the trouble spot according to the diagnosis code or perform normal failure phenomenon diagnosis.
	"NC" is displayed for one or more systems.	Write down all the systems for which "NC" is displayed, and proceed to CAN Bus Diagnostics Table.

CAN BUS LINE DIAGNOSTIC FLOW

1. M.U.T.-IIISE CAN bus diagnostics

The M.U.T.-IIISE diagnoses CAN bus lines in accordance with the following strategy.

Checking the communication condition of ECUs
The M.U.T.-IIISE narrows down troubles in circuit by itself. Its strategies are as follows.

ECU which cannot communicate with the M.U.T.-IIISE	Possible trouble spot	Logic for narrowing down trouble spot
ECU A	CAN bus line (a) and power supply system to ECU A	ECU A communicates with the M.U.T.-IIISE via CAN bus lines (a) and (b). The M.U.T.-IIISE judges that CAN bus line (b) is normal, because it can communicate with other ECUs. Possible trouble may be present in CAN bus line (a) or the power supply system to ECU A.
ECU C	CAN bus line (g) and power supply system to ECU C	ECU C communicates with the M.U.T.-IIISE via CAN bus lines (b), (c), (d) and (g). The M.U.T.-IIISE judges that CAN bus lines (b), (c) and (d) are normal, because it can communicate with ECUs B and D. Possible trouble may be present in CAN bus line (g) or the power supply system to ECU C.
ECU C and ECU D	Trouble in CAN bus line (d)	ECUs C ad D communicate with the M.U.T.-IIISE via CAN bus lines (b), (c), (d), (e) and (g). The M.U.T.-IIISE judges that CAN bus lines (b) and (c) are normal, because it can communicate with ECU B. Possible trouble may be present in CAN bus line (d), (e) or (g) or the power supply system to ECU D or C. CAN bus line (d) is shared by ECUs C and D when they communicate with the M.U.T.-IIISE, so CAN bus line (d) is suspected as ultimate cause. CAN bus line (g) or (e) and power supply systems to ECU C or D are also suspected as second cause.
ECU B and ECU D	CAN bus line (e) or (f) or power supply system to ECU B or D	ECUs B ad D communicate with the M.U.T.-IIISE via CAN bus lines (b), (c), (d), (e) and (f). The M.U.T.-IIISE judges that CAN bus lines (b), (c) and (d) are normal, because it can communicate with ECU C. Possible trouble may be present in CAN bus line (f) or (e) or the power supply system to ECU B or D.

2. If diagnosis code related to CAN communication is set as past trouble, isolate opens as described below.

note	If you pinpoint trouble spot according to diagnosis code, you should use time-out diagnosis code. diagnosis code related to failure information is set when the data to be set contains an error, so CAN bus line itself is probably normal.

note	Time-out diagnosis codes are stored in each ECU memory individually. Therefore, it is possible that these diagnosis codes have not been set simultaneously. If the trouble spot cannot be found when you diagnose by judging from multiple diagnosis codes, check the communication lines between each ECU.

Diagnosis code to be set	Possible trouble spot	Logic for narrowing down trouble spot
Time-out diagnosis code associated with ECU D is stored in ECU A, ECU B and ECU C.	Trouble in CAN bus line (e) and power supply system to ECU D	When time-out diagnosis code associated with ECU D is stored in ECU A, B and C, or time-out diagnosis code associated with ECUs A, B and C is stored in ECU D, CAN bus line (e) is suspected. When diagnosis code is not stored in ECU D, the power supply to ECU D is suspected.
Time-out diagnosis code associated with ECUs A, B, C and D is stored in ECU.
Time-out diagnosis code associated with ECU A is stored in ECUs B, C and D.	Trouble in CAN bus line (a) or (c) and power supply system to ECU A.	When time-out diagnosis code associated with ECU A is stored in ECUs B, C and D, or time-out diagnosis code associated with ECUs B, C and D is stored in ECU A, CAN bus line (a) or (c) is suspected. When diagnosis code is not stored in ECU A, the power supply to ECU A is suspected.
Time-out diagnosis code associated with ECUs B, C and D is stored in ECU A.
Time-out diagnosis codes associated with ECUs C and D are stored in ECU A and ECU B.	Trouble in CAN bus line (d)	If time-out diagnosis codes associated with ECUs C and D are stored in ECUs A and B, or time-out codes associated with ECUs A and B are stored in ECUs C and D, CAN bus line (d) is suspected. CAN bus line (g) or (e) and power supply systems to ECU C or D are also suspected as second cause.
Time-out diagnosis codes associated with ECUs A and B are stored in ECU C and ECU D.	Trouble in CAN bus line (d)