Information
- "CAN FUNDAMENTAL" of LAN Section describes the basic knowledge of the CAN communication system and the method of trouble diagnosis.
- For information related to a vehicle and inspection procedure, refer to "CAN".
Condition of Error Detection
DTC (e.g. U1000 and U1001) of CAN communication is indicated on SELF-DIAG RESULTS on CONSULT if a CAN communication signal is not transmitted or received between units for 2 seconds or more.
CAN COMMUNICATION SYSTEM ERROR
- CAN communication line open (CAN-H, CAN-L, or both)
- CAN communication line short (ground, between CAN communication lines, other harnesses)
- Error of CAN communication control circuit of the unit connected to CAN communication line
ERROR EXAMPLE
Note. Each vehicle differs in symptom of each control unit under fail-safe mode and CAN communication line wiring.
Example: Main Line Between Data Link Connector and ABS Actuator and Electric Unit (Control Unit) Open Circuit
Scheme 8
| Unit name | Major symptom |
|---|---|
| ECM | Engine torque limiting is affected, and shift harshness increases. |
| BCM | Reverse warning buzzer does not sound. The front wiper moves under continuous operation mode even though the front wiper switch being in the intermittent position. |
| EPS control unit | The steering effort increases. |
| Combination meter | The shift position indicator and OD OFF indicator turn OFF. The speedometer is inoperative. The odo/trip meter stops. |
| ABS actuator and electric unit (control unit) | Normal operation. |
| TCM | No impact on operation. |
| IPDM E/R | When the ignition switch is ON, The headlamps (Lo) turn ON. The cooling fan continues to rotate. |
Example: TCM Branch Line Open Circuit
Scheme 9
| Unit name | Major symptom |
|---|---|
| ECM | Engine torque limiting is affected, and shift harshness increases. |
| BCM | Reverse warning buzzer does not sound. |
| EPS control unit | Normal operation. |
| Combination meter | Shift position indicator and O/D OFF indicator turn OFF. Warning lamps turn ON. |
| ABS actuator and electric unit (control unit) | Normal operation. |
| TCM | No impact on operation. |
| IPDM E/R | Normal operation. |
Note. The model (all control units on CAN communication system are Diag on CAN) cannot perform CAN diagnosis with CONSULT if the following error occurs. The error is judged by the symptom.
| Error | Difference of symptom |
|---|---|
| Data link connector branch line open circuit | Normal operation. |
| CAN-H, CAN-L harness short-circuit | Most of the control units which are connected to the CAN communication system enter fail-safe mode or are deactivated. |
Example: Data Link Connector Branch Line Open Circuit
Scheme 10
| Unit name | Major symptom |
|---|---|
| ECM | Normal operation. |
| BCM | |
| EPS control unit | |
| Combination meter | |
| ABS actuator and electric unit (control unit) | |
| TCM | |
| IPDM E/R |
Note. When data link connector branch line is open, transmission and reception of CAN communication signals are not affected. Therefore, no symptoms occur. However, be sure to repair malfunctioning circuit.
Example: CAN-H, CAN-L Harness Short Circuit
Scheme 11
| Unit name | Major symptom |
|---|---|
| ECM | Engine torque limiting is affected, and shift harshness increases. Engine speed drops. |
| BCM | Reverse warning buzzer does not sound. The front wiper moves under continuous operation mode even though the front wiper switch being in the intermittent position. The room lamp does not turn ON. The engine does not start (if an error or malfunction occurs while turning the ignition switch OFF.) The steering lock does not release (if an error or malfunction occurs while turning the ignition switch OFF.) |
| EPS control unit | The steering effort increases. |
| Combination meter | The tachometer and the speedometer do not move. Warning lamps turn ON. Indicator lamps do not turn ON. |
| ABS actuator and electric unit (control unit) | Normal operation. |
| TCM | No impact on operation. |
| IPDM E/R | When the ignition switch is ON, The headlamps (Lo) turn ON. The cooling fan continues to rotate. |
Without PAST
| Item | PRESENT | Description |
|---|---|---|
| Initial diagnosis | OK | Normal at present |
| NG | Control unit error (Except for some control units) | |
| Transmission diagnosis | OK | Normal at present |
| UNKWN | Unable to transmit signals for 2 seconds or more. | |
| Diagnosis not performed | ||
| Control unit name (Reception diagnosis) | OK | Normal at present |
| UNKWN | Unable to receive signals for 2 seconds or more. | |
| Diagnosis not performed | ||
| No control unit for receiving signals. (No applicable optional parts) |
With PAST
| Item | PRESENT | PAST | Description |
|---|---|---|---|
| Transmission diagnosis | OK | OK | Normal at present and in the past |
| 1 - 39 | Normal at present, but unable to transmit signals for 2 seconds or more in the past. (The number indicates the number of ignition switch cycles from OFF to ON.) | ||
| UNKWN | 0 | Unable to transmit signals for 2 seconds or more at present. | |
| Control unit name (Reception diagnosis) | OK | OK | Normal at present and in the past |
| 1 - 39 | Normal at present, but unable to receive signals for 2 seconds or more in the past. (The number indicates the number of ignition switch cycles from OFF to ON.) | ||
| UNKWN | 0 | Unable to receive signals for 2 seconds or more at present. | |
| Not diagnosed | Diagnosis not performed. | ||
| No control unit for receiving signals. (No applicable optional parts) |
How to Use CAN Communication Signal Chart
The CAN communication signal chart lists the signals transmitted/received among control units. It is useful for detecting the root cause by finding a signal related to the symptom, and by checking transmission and reception unit.
Scheme 12
Scheme 13
INTERVIEW WITH CUSTOMER
Interview with the customer is important to detect the root cause of CAN communication system errors and to understand vehicle condition and symptoms for proper trouble diagnosis.
Points in interview
- What: Parts name, system name
- When: Date, Frequency
- Where: Road condition, Place
- In what condition: Driving condition/environment
- Result: Symptom
Notes for checking error symptoms
Scheme 14
- Check normal units as well as error symptoms. Example: Circuit between ECM and the combination meter is judged normal if the customer indicates tachometer functions normally.
- When a CAN communication system error is present, multiple control units may malfunction or go into fail-safe mode.
- Indication of the combination meter is important to detect the root cause because it is the most obvious to the customer, and it performs CAN communication with many units.
CREATE INTERVIEW SHEET
Fill out the symptom described by the customer, vehicle condition, and CAN system type on the interview sheet.
Scheme 15
DETECT THE ROOT CAUSE
CAN diagnosis function of CONSULT detects the root cause.