31
Troubleshooting and Testing
Pin
Circuit
1
Ground
2
Power
3
CAN-High
4
CAN-Low
4.11
ECU Circuit Testing
Electrical Checks
Verify vehicle batteries, charging system and fuses are in good working condition.
Load test battery and ignition circuits to ground at the ECU harness using a 2-4 amp sealed lamp and
verify lamp does not flicker and it is on steady.
Take measurements at the ECU harness pins.
Measurements should read as follows:
Location
Measurement
Supply Voltage, Battery to
chassis Ground
9.0-16.0V for 12V system
18.0-32.0V for 24V system
Supply Voltage, Ignition to
chassis Ground
9.0-16.0V for 12V system
18.0-32.0V for 24V system
ECU ground to chassis ground
Less than 1 ohm resistance
Main ground to chassis ground
Less than 1 ohm resistance
4.12
J1939 Serial Communications Testing
Electrical Checks
If the ABS ECU is the only ECU on the J1939 datalink which cannot communicate, then take
measurements at the ABS ECU connector. If other ECUs are not communicating, then troubleshoot the
vehicle datalink backbone and contact the vehicle OEM for technical assistance if required.
Check for devices that could be overloading the J1939 datalink slowing down communications.
Verify J1939 High and Low have correct voltage readings, Key ON, while datalink communications are
active.
For resistance measurements, the vehicle battery must be disconnected and the ignition must be OFF.
Measurements should read as follows:
Location
Measurement
Across J1939 High and Low
Approximately 60 ohms
J1939 Low voltage
0.1V-2.4V
J1939 High voltage
2.5V-5.0V
J1939 High or J1939 Low to
Ground or Power Supply
No continuity
