How To Interpret Can Bus Check Screen

When a communication stop is currently occurring, the probable malfunctioning part can be determined from the CAN bus check and by using the following methods.
NOTE:
The following CAN bus wiring diagram is provided only as an example. This wiring diagram is different from the actual wiring diagram for this vehicle.

HINT:
- When a communication stop is currently occurring, it is easier to determine the probable malfunctioning part from the CAN bus check rather than from communication DTCs.
- Wait for approximately 2 minutes after turning the engine switch on (IG) (or simulate the driving conditions that enable the malfunction to be reproduced) and select "CAN Bus Check". Then observe the communication status of each ECU on the screen.

If a communication error of only 1 ECU or sensor is indicated on the CAN Bus Check screen, a communication stop of the ECU or sensor is suspected.

Example: Open in both CAN branch lines of HV on the bus 4

Fig 1: Open In Both CAN Branch Lines Of HV On The Bus 4

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*a	Bus 2	*b	Bus 4
*c	Sub Bus	*d	V Bus
*e	Location of Malfunction	*f	Background color is red

HINT:

When there are communication stops, ECUs that are present in the vehicle may not be displayed on the CAN Bus Check screen.

If communication errors for multiple ECUs or sensors are indicated on the CAN Bus Check screen, then a communication stop of the ECU or sensor that shows a more serious communication stop (an ECU or sensor whose background color is red) is suspected.

Example: Open in a CAN branch line for HV on the bus 4

Fig 2: Open In A CAN Branch Line For HV On The Bus 4

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*a	Background color is red	*b	Background color intermittently becomes yellow or red
*c	Not displayed or background color is yellow or red	-	-

EXPLANATION OF CAN BUS CHECK SCREEN

Bus Type	Background Color	Connection Status
Bus	White	Communication has been normal.
	Yellow	Communication stop occurred at least once since the start of the CAN bus check, but communication is currently occurring (unstable communication).
	Red	Currently not communicating (either of the following): Not communicating since the start of the CAN bus check Communication occurred at least once since the start of the CAN bus check, but is currently not occurring.
	Not displayed	Either of the following: The central gateway ECU (network gateway ECU) has an internal malfunction or cannot communicate with the Techstream.4 No ECUs or sensors are connected to the bus.5
Sub bus with a gateway function equipped ECU that does not memorize connected ECUs or sensors*2	White	Communication has been normal since the start of the CAN bus check.
	Yellow	Communication stop occurred at least once since the start of the CAN bus check, but communication is currently occurring (unstable communication).
	Red	Communication occurred at least once since the start of the CAN bus check, but is currently not occurring.
	Not displayed	Communication stop has continued since the start of the CAN bus check.*1
Sub bus with a gateway function equipped ECU that memorizes connected ECUs and sensors*3	White	Communication has been normal.
	Yellow	Communication stop occurred at least once since the start of the CAN bus check, but communication is currently occurring (unstable communication).
	Red	Currently not communicating (either of the following): Not communicating since the start of the CAN bus check Communication occurred at least once since the start of the CAN bus check, but is currently not occurring.
	Not displayed	Either of the following: The gateway function equipped ECU cannot communicate with the central gateway ECU (network gateway ECU).6 No ECUs or sensors are connected to the sub bus.7

Gateway function equipped ECUs relay signals between ECUs and sensors connected to different buses.
*1: An ECU or sensor is installed to the vehicle but is not displayed on the "Communication Bus Check" screen.
*2: The gateway function equipped ECU does not memorize ECUs and sensors connected to its respective sub bus.
*3: The gateway function equipped ECU memorizes ECUs and sensors connected to its respective sub bus.
*4: When the central gateway ECU (network gateway ECU) has an internal malfunction or cannot communicate with the Techstream, the name of buses, sub buses, ECUs and sensors will not be displayed.
*5: When no ECUs or sensors are connected to a bus, the message "There is no system found on the communication Bus." will be displayed.
*6: When a gateway function equipped ECU cannot communicate with the central gateway ECU (network gateway ECU), the name of sub buses and ECUs or sensors connected to the sub bus will not be displayed.
*7: When no ECUs or sensors are connected to the sub bus, the message "There is no system found on the communication Bus." will be displayed.
The example of the CAN Bus Check screen in the illustration shows the result of electrical noise on the CAN bus which is caused by an open in a CAN branch line of HV is also unstable. In addition, in this example, MB is equipped with a gateway function. Therefore, communication is also unstable between the Sub bus ECUs of MB and the bus 4.
The example in the illustration shows that HV has a red background color on the CAN Bus Check screen. This indicates a more significant communication stop. In this case, a communication stop of HV is suspected.

If a communication error is indicated on both the bus 4 and Sub bus on the CAN Bus Check screen, suspect any communication stop displayed for the bus 4 first.

Example: Open in both CAN branch lines of MB on the bus 4

Fig 3: Open In Both CAN Branch Lines Of MB On The Bus 4

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Background color is red

Not displayed

HINT:

In the CAN bus check, it is possible to confirm the communication status of ECUs connected to the bus after connecting the Techstream to the DLC3. As for sub bus, it is possible to confirm which sub bus connected ECUs can communicate with a gateway function equipped ECU on the bus.
If a gateway function equipped ECU has a communication error, ECUs connected to the gateway function equipped ECU are also affected, and communication stops will be indicated.
The CAN Bus Check screen in the illustration shows that MB has a gateway function and a communication stop in MB is suspected.

If the CAN Bus Check screen indicates a communication stop only in the sub bus, a communication stop in the sub bus is suspected.
Example: Open in both CAN branch lines of MIR-R on the sub bus

Fig 4: Open In Both CAN Branch Lines of MIR-R On The Sub Bus
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*a Background color is red - -

HINT:
- A communication error in a sub bus does not affect the other buses.
- When a gateway function equipped ECU has memorized the ECUs that are connected to the sub bus, if any of the ECUs connected to the gateway function equipped ECU has a communication error, the background color changes to yellow or red. (The displayed name will not disappear.)

If both of the bus 2 main bus lines are open, ECUs or sensors that are located farther away from the central gateway ECU (network gateway ECU) than the open part will be displayed as a communication stop on the CAN Bus Check screen.

(In this case, HVB, R-MGC and ENG background color changes to red.)

Fig 5: HVB, R-MGC And ENG Background Color Change

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*a	Bus 2	*b	Bus 4
*c	Sub Bus	*d	V Bus
*e	Location of Malfunction	*f	Background color is red

HINT:

If a communication error occurs in an ECU, it is not displayed on the CAN Bus Check screen even though the ECU is present.

If both of the sub bus main bus lines are open, ECUs that are located farther away from the gateway function equipped ECU than the open part will be displayed as a communication stop on the CAN Bus Check screen.

(In this case, MIR-L background color changes to red.)

Fig 6: MIR-L Background Color Change

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*a	Bus 2	*b	Bus 4
*c	Sub Bus	*d	V Bus
*e	Location of Malfunction	*f	Background color is red

When any of the following malfunctions occur, CAN communication cannot be established and almost all ECUs and sensors on the bus show a communication error on the CAN Bus Check screen.

DETAILS OF MALFUNCTION

Short between CAN lines (CANH and CANL)

Short between a CAN line (CANH or CANL) and +B

Short between a CAN line (CANH or CANL) and ground

Open in a CAN main bus line

Fig 7: CAN Bus Check Screen

*a	When any of the following malfunctions occur on the bus 4	*b	When any of the following malfunctions occur on a sub bus
*c	Background color is red	*d	Not displayed

HINT:

When a malfunction occurs in the bus, almost all ECUs and sensors on the bus and sub bus indicate a communication error (almost all ECUs are not displayed). As communication with the gateway function equipped ECU that is connected to the bus stops, communication from the ECUs connected to the sub bus that is monitored by the gateway function equipped ECU also stops (these ECUs are not displayed).
When a malfunction occurs in a sub bus, almost all ECUs connected to the sub bus indicate a communication error.
A communication error in a sub bus does not affect the other buses.
The malfunctioning part can be determined by checking for a short circuit between CAN bus lines or between a CAN bus line and ground or +B short using an electrical tester.

If a communication error of all ECUs and sensors is indicated on the CAN Bus Check screen, a communication stop of the V bus (DLC3 - central gateway ECU (network gateway ECU)) is suspected.

Open in both CAN branch lines in the V bus

Fig 8: Open In Both CAN Branch Lines In The V Bus

*a	Bus 2	*b	Bus 4
*c	Sub Bus	*d	V Bus
*e	Location of Malfunction	*f	Not displayed

HINT:

When there is no communication between the Techstream and the vehicle, no ECUs or sensors will be displayed.