4

• Check for Diagnostic Trouble Codes (DTCs)
Are communication DTCs present in any of the modules?

Yes: Obtain a screen shot of the DTCs in ALL modules (ECM, ABS,
TCM, BC, etc....). Continue to Step 5
No: Evaluate complaint to determine if a data link issue is present.
Determine if faults were previously cleared.
Yes:

• Evaluate fault counts by modules
5
Do one (or more) modules show high fault counts of loss of
communication fault (Other modules would have low counts)?

• Load test the battery power, ignition power and ground
circuits at the module connector.
• If ALL power and ground circuits test okay, inspect the stub
wiring from the module connector to the backbone of the
data link.
• Ensure all terminals are properly seated and fully locked in
the connector.
• Inspect for spread terminals using a terminal test kit to pin
drag test the terminals.
• Verify the wires are pinned properly in the connector for
High(+) and Low(‐).
• If wiring goes to splice connector (heat shrink) cut open and
inspect, tug on each end and check for proper weld. You will
need to recrimp, solder and heat shrink after making this
inspection.
• Use the information starting at Step 6 to assist.
• If an issue is identified and repaired, re‐test for the
complaint.
• If no issue is identified, continue to Step 6
No: Continue to Step 6

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IK0800080 - J1939 Data Link Troubleshooting

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Yes: Continue to Step 7

6
• Measure the voltage at the ATA Diagnostic Connector
Terminal C to Gnd and D to Gnd.
• Use a multimeter or the Nexiq Device Tester‐ here

No: Continue to Step 8

Is there approximately 2.5 Vdc at each terminal?

7

Note: Terminal C should have slightly higher voltage than Terminal Yes:
D.
• A module not communicating can put 2.5Vdc on each data
Note: The voltages should not match
link wire.
• Monitor voltage at the 9 pin diagnostic connector while
unplugging modules
• If the voltage changes and communication resumes suspect
an issue at that module
◦ Load test the battery power, ignition power and ground
Does the voltage on C and D match?
wiring to that module
◦ Inspect the data link stub from the module connector to
the backbone
◦ If no wiring issue is located suspect a faulty module
• If no change in voltage is noted when modules are unplugged
inspect for data link High(+) and Low(‐) shorted together
No: Continue to Step 10

8

Does either terminal have abnormally high voltage?

9

Does either terminal have abnormally low voltage?

Yes: Check wiring for a Short to Power
No: Continue to Step 9
Yes: Check wiring for a Short to Ground
No: Return to Step 6 and re‐test.
Yes: Continue to Step 11
No:

10 Is the voltage on Terminal C (+) higher than Terminal D (‐)?

11

•
•
•
•
•

Disconnect the batteries.
All truck harnesses should be connected for this step.
Only the batteries should be disconnected.
Measure the resistance from Terminal C to D.
60 ± 5%

12

Do you have 57 ‐ 63 ohms?
Was the resistance measured at Step 11 (C to D) approximately
120 ohms?

13

Was the resistance measured at Step 11 (C to D) reading O.L
(Open)?

14 Was the resistance measured at Step 11 (C to D) near 40 ohms?

• Verify the wire is in the correct terminal location.
• Verify the wiring is spliced to the correct wire of the
backbone.
Yes: Continue to Step 16
No: Continue to Step 12
Yes: Continue to Step 18
No: Continue to step 13
Yes: Inspect stub wiring from the module connector to the
backbone of the data link. Repair wiring as needed and re‐test.
No: Continue to step 14
Yes: Inspect for body builder components that may have installed
a 3rd terminating resistor
No: Continue to Step 15

15 Was the resistance measured at Step 11 (C to D) < 40 ohms

Yes: Inspect data link wiring for High(+) and Low(‐) shorted
together
No: Return to Step 11 (Resistance out of range has not been
detected)

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IK0800080 - J1939 Data Link Troubleshooting

• Measure the resistance from Terminal C to Gnd

Yes: Continue to Step 17

16

No: Inspect data link wiring for a short to ground.

Does resistance measure > 1000 ohms?
17

Page 7 of 20

Yes: Continue to Step 18

• Measure the resistance from Terminal D to Gnd
• Unplug
themeasure
1702 connector.
Does
resistance
> 1000 ohms?
• Measure resistance on connector 1702 (Male Terminals)
◦ Note: This wiring harness runs outside the cab
• 120 ± 5%

18

No: Inspect data link wiring for a short to ground.
Yes: Continue to Step 19

No: Continue to Step 20

Is the resistance 114 ‐ 126 ohms?
• Unplug the 1702 connector.
It is recommended not to exceed ± 1 % tolerance between the
• Measure resistance on connector 1702 (Female Terminals)
two identical resistors.
◦ Note: This wiring harness runs to the pass through on
the right side the cab and continues through the dash
over to the 1701 connector on the left side of the cab
• 120 ± 5%
19
Is the resistance 114 ‐ 126 ohms?
• Locate Terminating Resistor #1.
Unplug the terminating
resistor
measurebetween
the resistance
It is•recommended
not to exceed
± 1 and
% tolerance
the
from terminal
A to B on the resistor.
two identical
resistors.
• Compare this to the resistance measured at Step 18
• 120 ± 5%

Yes: Wiring issue not detected. Re‐evaluate the complaint and
troubleshooting. Is the issue present?
If the issue is present, and the wiring checks okay, remove
modules from the data link, one module at a time until
communication is restored.
No: Continue to Step 21
Yes: Locate and repair open wire in the circuit between the 1702
connector and the terminating resistor.

20
Is the resistance 114 ‐ 126 ohms?

No: Replace the terminating resistor and re‐test.
• Locate Terminating Resistor #2.
• Unplug the terminating resistor and measure the resistance
If thisfrom
resistance
does
not
closely
match the resistance measured
terminal
A to
B on
the resistor.
Yes: Locate and repair open wire in the circuit between the 1702
at the
1702 connector
at Step
18, it may
indicate
high 19
resistance
• Compare
this to the
resistance
measured
at Step
connector and the terminating resistor.
in the
circuits.
• 120
± 5%
21
Is the resistance 114 ‐ 126 ohms?

No: Replace the terminating resistor and re‐test.

If this resistance does not closely match the resistance measured
connector at Step 19, it may indicate high resistance
( Back at
to the
Top1702
)
in the circuits.

Service Part(s) Information
Description

Part Number

Mating Connector

3519281C2

Bulk Data Link Jacketed Cable (Shielded)
25 Foot Roll

3572112R1
Bulk Data Link Jacketed Cable (Non‐Shielded )
50 Foot Roll

Terminating Resistor (3‐Pin Connector)

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IK0800080 - J1939 Data Link Troubleshooting

Page 8 of 20

120 ohm resistor: 3519178C91

Connector: 1667741C1
Terminal: 1661875C1

120 ohm resistor: 3769112C91

Connector: 3683465C1
Terminal: 3683464C1

Terminating Resistor (2‐Pin Connector)

( Back to Top )

Additional Resources
• SFN 02‐94 ‐ J1939 Troubleshooting
• Advanced Electrical Guide
• Master Service Information Page
( Back to Top )

Connector Views
• Always refer to the wiring schematic book for the vehicle you are working on
• Verify which specific engine you are working with. This will help ensure you are viewing the correct schematic with the correct terminal
locations on the ECM connector
J1939 Data Link (CAN) Pin out at major connectors
(Public Data Link Only)
Module

Connector

Diagnostic Connector

1650

J1939 Splice Adapter
Note: There is no terminal "I"

1024
1025
1026

J1939 Pins

Location

Pin (+)

Pin
(‐)

Dash panel left of
steering wheel
(Bus‐under dash right
of steering wheel)

C(+)

D(‐)

Center of dash panel

Connector View

GM AF

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Page 9 of 20

1702 ‐ Male Terminals
Goes to Engine

1702

Attached to wiper
bracket
Above valve cover

11(+) 17(‐)

1702 ‐ Female Terminals
Goes to Cab

1702

Attached to wiper
bracket
Above valve cover

11(+) 17(‐)

6018

Engine ECM

34(+) 47(‐)

ECM ‐ ISX 15L

6000

Engine ECM

22(+) 46(‐)

ECM ‐ ISB

6000

Engine ECM

22(+) 46(‐)

EIM ‐ MaxxForce 11 / 13 (EPA
07)
(Engine Interface Module)

6020

Left side of engine

12(+) 13(‐)

ECM ‐ N9 / N10

6020M

Right side of engine

61(+) 62(‐)

ECM
◦ N13
◦ MaxxForce 15
◦ MaxxForce 13 / 11
(EPA 10)

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IK0800080 - J1939 Data Link Troubleshooting

Page 10 of 20

6020M

Right side of engine
Mounted on air filter
bracket

53(+) 54(‐)

6020M

Left side of engine
76 Pin Chassis
connector
(Grey)

C61
(+)

DLCII Engine ECM

X3 ‐ 6020

Left side of engine
above starter (I6)
Top of left valve
cover (V8)

12(+) 13(‐)

DLC NavPak Engine ECM

6007

Engine ECM ‐ Black

19(+) 20(‐)

ECM ‐ MaxxForce 7 (EPA 10)

ECM
◦ MaxxForce DT / 9 /
10
(EPA 07 / EPA 10)
◦ MaxxForce 7 (EPA
07)
◦ MaxxForce 5 (EPA
07)

C62
(‐)

Engine DCU ‐ Doser Control
Unit
◦ MaxxForce DT / 9 /
10 (EPA 10)
◦ N9 / N10 (EPA 10)

6340

Collision Avoidance ‐ Bendix
Wingman

8903

Bendix Wingman DIU (Driver
Interface Unit)

1943M

ABS ‐ Bendix Air EC60

1400

14(+) 15(‐)

Front bumper

In cab ‐ Right kick
panel

1(+)

6(‐)

7(+)

6(‐)

8(+)

7(‐)

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IK0800080 - J1939 Data Link Troubleshooting

Page 11 of 20

ABS ‐ Bendix Air EC30

4024

Brake ECU

C3(+) D3(‐)

ABS ‐ Wabco Air

9513

Wabco ECU Grey

7(+)

6(‐)

ABS ‐ Wabco Air

1420

In cab ‐ Right kick
panel

3(+)

1(‐)

Collision Avoidance ‐ Wabco
OnGuard

8902

Front bumper

4(+)

5(‐)

Wabco OnGuard DIU (Driver
Interface Unit)

1944

A(+)

B(‐)

Wabco Hydraulic Full Power
Brakes

9511

ECU is mounted on
HCU
Left Frame Rail