Scan Tool Testing and Procedures

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

CIRCUIT DESCRIPTION
The Class II Serial Data circuit to the Data Link Connector (DLC) allows bi-directional communication between the Vehicle Control Module (VCM) and the scan tool. This is accomplished through pin 2 of the DLC. If communication between the scan tool and the VCM cannot be established, the procedure in the DLC Diagnosis table should be used to diagnose the condition.

DIAGNOSTIC AIDS
Check for the following items:
^ For the VCM to establish communication with the scan tool, system voltage must be between 9.0 and 16.0 volts. If the system voltage is not within this range, refer to Charging System Check in Starting and Charging for diagnosis. Starting and Charging
^ Ensure that the correct application, such as model year, truckline, VIN code, has been selected on the scan tool.
An intermittent may be caused by any of the following conditions:
^ A poor connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Diagrams.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Diagrams.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if the scan tool is operating correctly.
6. This step monitors the actively communicating modules with the scan tool Diagnostic Circuit Check function. An active module is a module that is successfully communicating on the Class 2 Serial Data line with the scan tool. An inactive module is a module which had previously established communications with the scan tool, but currently is not communicating. If a module is not listed at all, then the module never successfully established communications with the scan tool.
7. This step isolates the VCM by disconnecting all the other components on the Class 2 Serial Data circuit. After making repairs, it is necessary to clear the DTCs from the modules that can communicate. Clearing the DTCs will avoid future misdiagnoses.
12. This step determines if the voltage is not available at the DLC due to an open battery feed fuse. If the fuse is open, determine if the open was due to a short in the battery feed circuit before replacing the fuse.