LAN System Basic Inspection
LAN System: Basic Inspection
Information Needed for Trouble Diagnosis
CAN communication system performs trouble diagnosis with the following tools.
How to Use CAN Communication Signal Chart
The CAN communication signal chart lists the signals needed for trouble diagnosis. It is useful for detecting the root cause by finding a signal related to the symptom, and by checking transmission and reception unit.
Trouble Diagnosis Flow Chart
Trouble Diagnosis Procedure
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
NOTE:
- 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.
Inspection of Vehicle Condition
- Check whether or not DTC of CAN communication is indicated on "DTC check" by SDT.
NOTE:
Root cause cannot be detected using the procedure in this section if DTC of CAN communication is not indicated.
- Check whether the symptom is reproduced or not.
NOTE:
- Do not turn the ignition switch OFF or disconnect the battery cable while reproducing the error. The error may temporarily correct itself, making it difficult to determine the root cause.
- The procedures for present errors differ from the procedures for past errors. Refer to "DETECT THE ROOT CAUSE".
Check of CAN System Type (How to Use CAN System Type Specification Chart)
Determine CAN system type based on vehicle equipment. Then choose the correct diagnosis sheet.
NOTE:
There are two styles for CAN system type specification charts. Depending on the number of available system types, either style A or style B may be used.
CAN System Type Specification Chart (Style A)
NOTE:
CAN system type is easily checked with the vehicle equipment identification information shown in the chart.
CAN System Type Specification Chart (Style B)
NOTE:
CAN system type is easily checked with the vehicle equipment identification information shown in the chart.
Create Interview Sheet
Fill out the symptom described by the customer, vehicle condition, and CAN system type on the interview sheet.
Interview Sheet (Example)
Collect Data
Collect SDT Data
Print out or save the following SDT data.
- DTC check
- Bus check
NOTE:
Some items may not be needed depending on CAN system type of vehicle.
Create On-board Diagnosis Copy Sheet
Display the trouble diagnosis result of CAN communication with the on-board diagnosis function on the vehicle monitor, etc. Copy them on the on-board diagnosis copy sheet.
NOTE:
For some models, CAN communication diagnosis result is received from the vehicle monitor. (SDT is not available.)
Create Diagnosis Sheet
NOTE:
Be sure to use the diagnosis sheet for the correct CAN system type.
Print Diagnosis Sheet
Print the diagnosis sheet for the applicable CAN system type.
Check Collected Data
Check that all ECUs are received, referring to "ECU list" on the "Communication Bus Check" under "Bus Check" menu of SDT.
NOTE:
For abbreviations, refer to [How to Use This Section] How to Use This Section.
Detect the Root Cause
Identify the root cause using the created diagnosis sheet.
Identifying the root cause
- Draw a line on the diagnosis sheet to indicate the possible cause. Narrow the search.
NOTE:
- Color-code when drawing lines.
- Do not draw a line onto a existing line.
- Drawing a line is not necessary if the circuit is shorted. Refer to "Present Error - Short Circuit -", "Past Error - Short Circuit -".
Refer to the following for details of the trouble diagnosis procedure.
- "Present Error - Open Circuit -"
- "Present Error - Short Circuit -"
- "Past Error - Open Circuit -"
- "Past Error - Short Circuit -"
NOTE:
When the root cause appears to be a branch line or short circuit, be sure to check the control unit as well as the communication line.
Present Error - Open Circuit -
Identify the error circuit using information from the "Bus check"
1) Check the items indicated in "ECU list" on the "Communication Bus Check" under "Bus Check" menu of SDT. Draw a line on the diagnosis sheet to indicate the error circuit.
NOTE:
CAN communication line has no error if units other than Diag on CAN units are not indicated. An error may be on the power supply of the control unit, DDL1 line or DDL2 line.
a) "TCM" which is Diag on CAN unit, is not indicated on "ECU list" on the "Communication Bus Check" under "Bus Check" menu of SDT. This indicates that DLC is not receiving a signal from TCM. Draw a line to indicate an error between DLC and TCM (line 1-a in the figure below).
NOTE:
- Diag on CAN units are not indicated on the "ECU list" on the "Communication Bus Check" under "Bus Check" menu of SDT when the CAN line between Diag on CAN unit and the data link connector is open.
- For a description of Diag on CAN, refer to [DIAG On CAN: Description] CAN Description.
2) Bus check: Check each item on "Bus check". Draw a line on the diagnosis sheet to indicate the error circuit.
a) Reception item of "ENGINE": On "TCM", "UNKWN" is indicated. This means ECM cannot receive the signal from TCM. Draw a line to indicate an error between ECM and TCM (line 2-a in the figure below).
NOTE:
If "UNKWN" is indicated on "TRANSMIT DIAG", then the control unit cannot transmit CAN communication signal to each unit. Draw a line between the control unit and the splice.
b) Reception item of "ADAPTIVE LIGHT": On "TCM", "UNKWN" is indicated. This means AFS cannot receive the signal from TCM. Draw a line to indicate an error between AFS and TCM (line 2-b in the figure below).
c) Reception item of "MULTI AV": "UNKWN" is not indicated. This indicates normal communication between AV and its receiving units. Do not draw any line.
d) Reception item of "BCM": On "TCM", "UNKWN" is indicated. This means BCM cannot receive the signal from TCM. Draw a line to indicate an error between BCM and TCM (line 2-d in the figure below).
e) Reception item of "EPS" and "INTELLIGENT KEY": "UNKWN" is not indicated. This indicates normal communication between EPS and I-KEY and their receiving units. Do not draw any line.
NOTE:
On bus check (without PAST), "UNKWN" is indicated even though the item is not used in the trouble diagnosis. For the details of each item on bus check, refer to [Bus Check] Bus Check.
f) Reception item of "METER/M&A": On "TCM", "UNKWN" is indicated. This means M&A cannot receive the signal from TCM. Draw a line to indicate an error between M&A and TCM (line 2-f in the figure below).
g) Reception item of "AUTO DRIVE POS.": On "TCM", "UNKWN" is indicated. This means ADP cannot receive the signal from TCM. Draw a line to indicate an error between ADP and TCM (line 2-g in the figure below).
h) Reception item of "ABS": "UNKWN" is not indicated. This indicates normal communication between ABS and its receiving units. Do not draw any line.
i) Reception item of "IPDM E/R": "UNKWN" is not indicated. This indicates normal communication between IPDM-E and its receiving units. Do not draw any line.
3) Based on information received from "Bus check", place a check mark on the known good CAN communication line between ECM and IPDM-E.
a) Through the previous procedure, the circuit between ADP splice and TCM has the most amount of lines (shade 3-a in the figure below).
b) Place a check mark on the known good lines to establish the error circuit.
Reception item of "IPDM E/R": On "ECM", "OK" is indicated. IPDM-E communicates normally with ECM. Put a check mark on the normal circuit between ECM and IPDM-E (check mark 3-b in the figure below).
4) Through the above procedure, the error is detected in the TCM branch line (shaded in the figure below).
NOTE:
For abbreviations, refer to [How to Use This Section] How to Use This Section.
5) Perform the inspection for the detected error circuit. For the inspection procedure, refer to "MALFUNCTION AREA CHART".
Present Error - Short Circuit -
When the symptoms listed below exist, a short circuit of the CAN communication line is a possible cause.
Received data
Error symptom
- Most the units connected to the CAN communication system go into fail-safe mode or are deactivated.
Inspection procedure
- Refer to "MALFUNCTION AREA CHART".
Past Error - Open Circuit -
Review CAN communication signal chart based on information received from the interview with the customer and on past error information from DTC check and bus check.
6) DTC check: Inspect the control units indicating "U1000" or "U1001" on DTC check.
7) Bus check (with PAST): Check the bus check (with PAST) of units indicating "U1000" or "U1001" on DTC check. Draw a line on the diagnosis sheet to indicate the possible error circuit.
NOTE:
For the details of each indication on bus check, refer to [Bus Check] Bus Check.
a) Reception item of "ENGINE": "VDC/TCS/ABS", "3" is indicated in the "PAST". This means ECM could not receive the signal from ABS in the past. Draw a line between ECM and ABS (line 2-a in the figure below).
b) Reception item of "METER/M&A": "VDC/TCS/ABS", "3" is indicated in the "PAST". This means M&A could not receive the signal from ABS in the past. Draw a line between M&A and ABS (line 2-b in the figure below).
c) Reception item of "TRANSMISSION": "VDC/TCS/ABS", "3" is indicated in the "PAST". This means TCM could not receive the signal from ABS in the past. Draw a line between TCM and ABS (line 2-c in the figure below).
8) Bus check (without PAST): Check the bus check (without PAST) of units indicating "U1000" or "U1001" on DTC check. Draw a line on the diagnosis sheet to indicate the possible error circuit.
NOTE:
- While an error occurred in the past according to DTC check, it is unclear which signal is not received. Assume that errors were detected from all reception items.
- Draw a single line among the unit and all reception items. (Work flow differs from bus check (with PAST).)
a) Reception item of "EPS": Assume that the unit could not receive the signals from ECM, ABS, and M&A. Draw a line among EPS, ECM, ABS, and M&A (line 3-a in the figure below).
b) Reception item of "ABS": Assume that the unit could not receive the signal from ECM. Draw a line between ABS and ECM (line 3-b in the figure below).
9) Search for the possible cause using CAN communication signal chart using information from the interview with the customer.
NOTE:
For the details of CAN communication signal, refer to [CAN Communication Signal Chart] Signal Chart.
a) ABS warning lamp turned ON and speedometer did not move: This means that "ABS warning lamp signal" and "Vehicle speed signal" could not communicate between M&A and ABS (4-a in the figure below).
b) The tachometer moved normally: This means that "Engine speed signal" could communicate normally between ECM and M&A (4-b in the figure below).
10) Fill out the diagnosis sheet based on information from step 4.
a) The ABS warning lamp turned ON and speedometer did not move: Assume that a possible cause is no communication between M&A and ABS. Draw a line between M&A and ABS. (Line 5-a in the figure below).
b) The tachometer moved normally: Put check marks between ECM and M&A. The circuit between ECM and M&A is functioning properly (check marks 5-b in the figure below).
11) The circuit which has the most amount of lines are the possible cause. Error is detected from ABS actuator and electric unit (control unit) branch line (shaded in the figure below).
NOTE:
For abbreviations, refer to [How to Use This Section] How to Use This Section.
12) Perform the inspection procedure for the possible cause. Refer to "MALFUNCTION AREA CHART".
Past Error - Short Circuit -
When the symptoms listed below exist, a short circuit of the CAN communication line is a possible cause.
