Nissan Sentra Service Manual: System description

System

Can communication system

Can communication system : system description

CAN (Controller Area Network) is a serial communication line for real time application. It is an on-vehicle multiplex communication line with high data communication speed and excellent error detection ability. Many electronic control units are equipped onto a vehicle, and each control unit shares information and links with other control units during operation (not independent). In CAN communication, control units are connected with 2 communication lines (CAN-H line, CAN-L line) allowing a high rate of information transmission with less wiring.

Each control unit transmits/receives data but selectively reads required data only.

Diag on can

Diag on can : system description

System diagram

Description

“Diag on CAN” is a diagnosis method which uses the CAN communication line for the communication between the control unit and the diagnostic tool.

Trouble diagnosis

Component description

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

When dtc of can communication is indicated even though can communication system is normal

• Removal/installation of parts: Error may be detected when removing and installing CAN communication unit and related parts while turning the ignition switch ON. (A DTC except for CAN communication may be detected.)
• Fuse blown out (removed): can communication of the unit may cease.
• Voltage drop: Error may be detected if voltage drops due to discharged battery when turning the ignition switch ON (Depending on the control unit which carries out CAN communication).
• Error may be detected if the power supply circuit of the control unit, which carries out can communication, malfunctions (depending on the control unit which carries out can communication).
• Error may be detected if reprogramming is not completed normally.

Note:

Can communication system is normal if dtc of can communication is indicated on self-diag results of consult under the above conditions. Erase the memory of the self-diagnosis of each control unit.

Symptom when error occurs in can communication system

In CAN communication system, multiple control units mutually transmit and receive signals. Each control unit cannot transmit and receive signals if any error occurs on CAN communication line. Under this condition, multiple control units related to the root cause malfunction or go into fail-safe mode.

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

Example: tcm branch line open circuit

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.

Example: data link connector branch line open circuit

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

Can diagnosis with consult

Can diagnosis on consult extracts the root cause by receiving the following information.

• Response to the system call
• Control unit diagnosis information
• Self-diagnosis
• Can diagnostic support monitor

Self-diagnosis

If communication signals cannot be transmitted or received among control units communicating via CAN communication line, CAN communication-related DTC is displayed on the CONSULT “Self Diagnostic Result” screen.

Note:

The following table shows examples of CAN communication-related DTC. For other DTC, refer to the applicable sections.

Can diagnostic support monitor

Monitor item (consult)

Example: can diag support mntr indication

Without past

With past

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.

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