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 ECU B on the V bus

Fig 1: Open In Both CAN Branch Lines Of ECU B

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*a	V Bus	*b	Sub Bus
*c	Terminating Resistor	*d	Location of Malfunction
*e	Not displayed or background color changes to red or yellow	*f	CAN Bus Check Screen

HINT:

When there are communication stops, ECUs are present in the vehicle even though they are not 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 a sensor which is not displayed) is suspected.

Example: Open in a CAN branch line for ECU D on the V bus

Fig 2: Open In A CAN Branch Line For ECU D On V Bus

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*a	Background color periodically changes to yellow or red
*b	Not displayed or background color is yellow or red
*c	Not displayed

EXPLANATION OF CAN BUS CHECK SCREEN

Bus Type	Background Color	Connection Status
V Bus	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 was established at least once since the start of the CAN bus check, but communication is currently not occurring (unstable communication).
	Not displayed	Communication stop has continued since the start of the CAN bus check.*1
Sub Bus (gateway function equipped ECU that does not have history of connected ECUs)*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 was established at least once since the start of the CAN bus check, but communication is currently not occurring (unstable communication).
	Not displayed	Communication stop has continued since the start of the CAN bus check.*1
Sub Bus (gateway function equipped ECU that has history of connected ECUs)*3	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	Currently not communicating (either of the following): Communication stop has continued since the start of the CAN bus check. Communication was established at least once since the start of the CAN bus check, but communication is currently not occurring.
	Not displayed	Either of the following: If a gateway function equipped ECU cannot communicate, sub bus and ECUs connected to the sub bus will not be displayed. If no ECUs are connected to the sub bus, "There is no system found on the Communication Bus" will be displayed.

HINT:

Gateway function equipped ECUs relay signals between the ECUs connected to the different buses.
*1: ECUs that are present in the vehicle but are not displayed on the CAN Bus Check screen.
*2: Gateway function equipped ECU that does not memorize the sub bus ECUs that are connected to it.
*3: Gateway function equipped ECU that memorizes the sub bus ECUs that are connected to it.
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 ECU D (output from the other branch line is unstable) and the communication of ECU C is also unstable. In addition, in this example, ECU C is equipped with a gateway function. Therefore, communication is also unstable between the sub bus ECUs of ECU C and the V bus.
The example in the illustration shows that ECU D is not displayed on the CAN Bus Check screen. This indicates a more significant communication stop. In this case, a communication stop of ECU D is suspected.

If a communication error is indicated on both the V bus and sub bus on the CAN Bus Check screen, suspect any communication stop displayed for the V bus first.
Example: Open in both CAN branch lines of ECU C on the V bus

Fig 3: Open In Both CAN Branch Lines Of ECU C On V Bus
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*a Not displayed or background color changes to red

HINT:
- In the CAN bus check, it is possible to confirm the communication status of ECUs connected to the V bus after connecting the Techstream to the DLC3. As for sub buses, it is possible to confirm which sub bus connected ECUs can communicate with a gateway function equipped ECU on the V 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 ECU C has a gateway function and a communication stop in ECU C 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 ECU G on the sub bus

Fig 4: Open In Both CAN Branch Lines Of ECU G
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*a Background color changes to red

HINT:
- A communication error in a sub bus does not affect the V bus or 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 V bus main bus lines are open, ECUs or sensors that are located farther away from the DLC3 than the open part will be displayed as a communication stop on the CAN Bus Check screen.

(In this case, ECU A and B are not displayed or their background color changes to red.)

Fig 5: V Bus Main Bus Lines Are Open, ECUs Or Sensors

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*a	V Bus	*b	Sub Bus
*c	Terminating Resistor	*d	Location of Malfunction
*e	Not displayed or background color is red	*f	CAN Bus Check Screen

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, ECU I and J are not displayed or their background color changes to red.)

Fig 6: Sub Bus Main Bus Lines Are Open, ECUs

*a	V Bus	*b	Sub Bus
*c	Terminating Resistor	*d	Location of Malfunction
*e	Not displayed or background color is red	*f	CAN Bus Check Screen
*g	Gateway Function Equipped ECU	-	-

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.

Fig 7: Malfunctions Occur On V bus & Malfunctions Occur On A Sub Bus

*a	When any of the following malfunctions occur on the V bus
*b	When any of the following malfunctions occur on a sub bus
*c	Not displayed

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

HINT:

When a malfunction occurs on the V bus, almost all ECUs and sensors on the V 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 V 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 V bus or 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.