MICROSCAN User Manual - Snap-on

Appendix A Troubleshooting
OBD-II/EOBD vehicles have few problems communicating with a scan tool. However, problems
with the wiring or other circuit parts on the vehicle may prevent communication between the scan
tool and the vehicle electronic control module (ECM). When this happens, a “no communication”
message displays on the screen. A vehicle that fails to perform a test can also be a symptom of a
driveability problem.
A.1 Communication Problems
When the screen displays a “No Communication” message, it means the scan tool and the vehicle
control module are not communicating with each other.
The following conditions will cause the scan tool to display a “No Communication” message:
• The scan tool is unable to establish a communication link with the vehicle.
• Bent, missing, or otherwise damaged connector pins.
• A loose connection.
• A blown vehicle fuse.
• A wiring fault on the vehicle.
Connect the scan tool to another vehicle, if it operates correctly the problem in the vehicle.
A.1.1 Erratic or No Communication
A steady source of vehicle power is required for the scan tool to properly operate during testing.
The data cable provides power to the unit through the vehicle data link connector (DLC). Poor or
loose cable connections or damaged cables can cause erratic or no communication.
Make sure all connections are clean and tight. Measure resistance on suspect cables. A data
cable may appear perfectly normal, but have internal damage from being pinched, kinked, or
smashed that creates an open circuit. Use an ohmmeter to check for pin-to-pin continuity between
the connectors at either end of the data cable. There should be very little resistance in the cable
and readings should be equal for all of the circuits.
A.1.2 Testing the Data Link Connector
Unfortunately, vehicle manufacturers have different interpretations of OBD-II requirements. This
makes it rather difficult to define a specific approach to DLC problem diagnosis. For example,
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