54C-CAN BUS LINE DIAGNOSTICS FLOW

EXPLANATION ABOUT THE SCAN TOOL (M.U.T.-III) CAN BUS DIAGNOSTICS

Scan tool (M.U.T.-III) CAN bus diagnostics carries out the three checks below automatically, and then displays current condition of the CAN bus lines according to the check results.

CAN BUS LINE DIAGNOSTIC FLOW

1. Scan tool CAN bus diagnostics

Scan tool (M.U.T.-III) diagnoses CAN bus lines in accordance with the following strategy.

Checking the communication condition of ECUs
Scan tool (M.U.T.-III) narrows down troubles in circuit by itself. Its strategies are as follows.

ECU which cannot communicate with the scan tool	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 scan tool (M.U.T.-III) via CAN bus lines (a) and (b). The scan tool (M.U.T.-III) 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 scan tool (M.U.T.-III) via CAN bus lines (b), (c), (d) and (g). The scan tool (M.U.T.-III) 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 scan tool (M.U.T.-III) via CAN bus lines (b), (c), (d), (e) and (g). The scan tool (M.U.T.-III) 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 scan tool (M.U.T.-III), 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 scan tool (M.U.T.-III) via CAN bus lines (b), (c), (d), (e) and (f). The scan tool (M.U.T.-III) 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 diagnostic trouble code related to CAN communication is stored as past trouble, isolate opens as described below.

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

note

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

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