Mazda 6. Manual - part 346

ON-BOARD DIAGNOSTIC [MULTIPLEX COMMUNICATION SYSTEM] 

T–140–1

T

T–140BODY ELECTRICAL SYSTEM

MULTIPLEX COMMUNICATION SYSTEM

A6E816255430W01

Outline

• In case the controller area network (CAN) system is malfunctioning, read the DTCs of the following modules, 

using the SST (WDS or equivalent) to determine the malfunctioning system.
— PCM
— DSC HU/CM (with DSC)
— ABS (ABS/TCS) HU/CM (with ABS (ABS/TCS)
— Instrument cluster

Flowchart

• Use the following flowchart to verify the cause of the trouble.

End Of Sie

ON-BOARD DIAGNOSTIC [MULTIPLEX COMMUNICATION SYSTEM]

Repair the malfunctioning part by 
following the DTC inspection.

A

Inspect the power supply and the ground circuits for any units 
that do not respond.
Are they normal?

Repair the malfunctioning part.

A

A

B

START

Using the SST (WDS or equivalent), verify if DTCs are displayed for PCM, ABS (ABS/TCS) HU/CM  (with ABS (ABS/TCS)), 
DSC HU/CM (with DSC) and instrument cluster.
Are any DTCs displayed?

Yes

Are any DTCs other than the following displayed?
   PCM: U0073, U0121, U0155
   ABS (ABS/TCS) HU/CM, DSC HU/CM,
      Instrument cluster: U1900, U2516

No

END

No

No

Yes

Are any of the following DTCs displayed?
    PCM: U0073, U0121, U0155
    ABS (ABS/TCS) HU/CM, DSC HU/CM,
       Instrument cluster: U1900, U2516

Yes

Yes

Narrow down CAN system malfunction location.

Using the SST (WDS or equivalent), verify if DTCs 
are displayed for PCM, ABS (ABS/TCS) HU/CM, 
DSC HU/CM and instrument cluster.
Are any DTCs displayed?

No

Using the SST (WDS or equivalent), clear DTCs 
stored in each module.

END

Yes

No

Turn the ignition switch to the LOCK position.
Inspect the wiring harness and connector between any unit that 
does not respond and the DLC-2. 
   PCM

—

DLC-2

       2R

—

CAN_L

       2U

—

CAN_H

   ABS (ABS/TCS) HU/CM

—

DLC-2

       X

—KLN

   DSC HU/CM

—

DLC-2

       AB

—

KLN

   Instrument cluster

—

DLC-2

       2W

—

CAN_L

       2X

—

CAN_H

Are the wiring harnesses and connectors normal?

Is there a response from the PCM, ABS (ABS/TCS) HU/CM, 
DSC HU/CM and/or instrument cluster?

No

Yes

No

Yes

Repair the malfunctioning part by following the 
DTC inspection.

Repair the malfunctioning part.

A6E8162L001

ON-BOARD DIAGNOSTIC [MULTIPLEX COMMUNICATION SYSTEM] 

T–141

T

TBODY ELECTRICAL SYSTEM

End Of Sie

ON-BOARD DIAGNOSTIC [MULTIPLEX COMMUNICATION SYSTEM]

Connect each unit connector.
Turn the ignition switch to the ON position.
Measure the voltage between DLC-2 terminals CAN_L and CAN_H.
Is the voltage 2.0—3.0 V?

Turn the ignition switch to the LOCK position.
Measure the resistance between DLC-2 terminals CAN_L and 
CAN_H.
Is the resistance 59—65 ohms?

Replace any units that 
do not respond.

Disconnect the PCM connector.
Measure the resistance between PCM 
connector terminals 2R and 2U.
Is the resistance 118—130 ohms?

Replace the PCM.

Disconnect the instrument cluster connector.
Measure the resistance between instrument cluster connector 
terminals 2W and 2X.
Is the resistance 118—130 ohms?

Replace the instrument
cluster.

Turn the ignition switch to the LOCK position.
Disconnect the connector of any unit that does not respond.
(If there are two or more units that do not respond, 
disconnect only one of the units.)
Turn the ignition switch to the ON position.
Measure the voltage between DLC-2 terminals CAN_L and 
CAN_H.
Is the voltage 2.0—3.0 V?

The disconnected unit or the 
related wiring harness may 
have a malfunction.

Replace the disconnected unit.

Replace the related wiring harness.

The disconnected 
unit is normal.

Are all units that do not respond disconnected?

Inspect if the related wiring harnesses (CAN_L 
and/or CAN_H) have been shorted (to power 
supply or ground).
If a short is found, replace the related wiring 
harness.

Yes

No

B

A

A

A

A

A

A

Turn the ignition switch to the LOCK position.
Verify the continuity between the following connector terminals of any disconnected unit.
    PCM connector: 2R (CAN_L)—other terminals, 2U (CAN_H)—other terminals
    ABS (ABS/TCS) HU/CM connector: R (CAN_L)—other terminals, 
                                                             O (CAN_H)—other terminals 
    DSC HU/CM connector: AF (CAN_L)—other terminals, AG (CAN_H)—other terminals
    Instrument cluster connector: 2W (CAN_L)—other terminals, 2X (CAN_H)—other terminals
Is there continuity?

Yes

No

Yes

No

Yes

No

Yes

No

Yes

No

Yes

No

A6E8162L002

T–142

ON-BOARD DIAGNOSTIC [MULTIPLEX COMMUNICATION SYSTEM] 

DTC TABLE

A6E816255430W02

End Of Sie

PID/DATA MONITOR TABLE

A6E816255430W03

End Of Sie

PROCEDURES FOR DETERMINING THE LOCATION OF A MALFUNCTION

A6E816255430W04

System Wiring Diadram

DTC

Malfunction location

Related module

Page

U0073

CAN system communication error

PCM

(See 

T–144 DTC U0073, 

U1900, U2516

)

U0121

Communication error to ABS (ABS/TCS) HU/CM 
or DSC HU/CM

—

U0155

Communication error to instrument cluster

U1900

CAN system communication error

• ABS (ABS/TCS) HU/CM (with 

ABS (ABS/TCS)

• DSC HU/CM (with DSC)

• Instrument cluster

(See 

T–144 DTC U0073, 

U1900, U2516

)

U2516

CAN system wiring harness open and short 
circuit

PID name (definition)

Condition

Specification

Related module

Terminal

IC_MSG
(Missing message from the 
instrument cluster)

Present

Circuit in the instrument cluster 
is normal.

ABS (ABS/TCS) 
HU/CM or DSC HU/
CM

• ABS (ABS/TCS) 

HU/CM: O, R

• DSC HU/CM: AF, 

AG

• Instrument cluster: 

2W, 2X

Not Present

Circuit in the instrument cluster 
is abnormal.

ABS_MSG
(Missing message from the 
ABS (ABS/TCS) HU/CM or 
DSC HU/CM)

Present

Circuit in the ABS (ABS/TCS) 
HU/CM or DSC HU/CM is 
normal.

Instrument cluster

Not Present

Circuit in the ABS (ABS/TCS) 
HU/CM or DSC HU/CM is 
abnormal.

PCM_MSG
(Missing message from the 
PCM)

Present

Circuit in the PCM is normal.

• ABS (ABS/TCS) 

HU/CM or DSC 
HU/CM

• Instrument 

cluster

Not Present

Circuit in the PCM is abnormal.

A6E8162W002

ON-BOARD DIAGNOSTIC [MULTIPLEX COMMUNICATION SYSTEM] 

T–143

T

PCM

1. Check the display of DTC U0121 and/or U0155, using the SST (WDS or equivalent). (See 

T–142 DTC TABLE

.)

2. Referring to the following table, determine the malfunctioning part of the CAN system.

X: Normal

—: Communication error

ABS/TCS HU/CM or DSC HU/CM

1. Accec and monitor the “PCM MSG” and “IC MSG”of PID using the SST (WDS or equivalent).
2. Referring to the PID/DATA MONITOR, confirm the display status of the PID. (See 

T–142 PID/DATA MONITOR 

TABLE

.)

3. Referring to the following table, determine the malfunctioning part of the CAN system.

X: Normal

—: Communication error

Instrument Cluster

1. Accec and monitor the “PCM MSG” and “ABS MSG” of PID using the SST (WDS or equivalent).
2. Referring to the PID/DATA MONITOR, confirm the display status of the PID. (See 

T–142 PID/DATA MONITOR 

TABLE

.)

3. Referring to the following table, determine the malfunctioning part of the CAN system.

X: Normal

—: Communication error

End Of Sie

Module

Communication status

Malfunction location

• ABS (ABS/TCS) HU/CM

• DSC HU/CM

Instrument cluster

PCM

—

—

• Wiring harness A

• PCM

—

X

• Wiring harness B

• ABS (ABS/TCS) HU/CM

• DSC HU/CM

X

—

• Wiring harness C

• Instrument cluster

Module

Communication status

Malfunction location

PCM

Instrument cluster

• ABS (ABS/TCS) 

HU/CM

• DSC HU/CM

—

—

• Wiring harness B

• ABS (ABS/TCS) HU/CM

• DSC HU/CM

—

X

• Wiring harness A

• PCM

X

—

• Wiring harness C

• Instrument cluster

Module

Communication status

Malfunction location

PCM

• ABS (ABS/TCS) HU/CM

• DSC HU/CM

Instrument cluster

—

—

• Wiring harness C

• Instrument cluster

—

X

• Wiring harness A

• PCM

X

—

• Wiring harness B

• ABS (ABS/TCS) HU/CM

• DSC HU/CM