Refer to Engine Controls electrical schematic diagrams for wiring view.
Circuit Description
The Class II serial data circuit to the Data Link Connector (DLC) allows bi-directional communication between the VCM and the scan tool. This is accomplished through terminal 2 of the DLC. If communication between the scan tool and the VCM cannot be established, this diagnostic procedure 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 for diagnosis. |
| • | Ensure that the correct application (model year, truckline, VIN code) has been selected on the scan tool. |
| • | An intermittent may be caused by a poor connection, rubbed through wire insulation, or a broken wire inside the insulation. Check for a poor connections or a damaged harness. Inspect the VCM harness and the connectors for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. |
Test Description
The numbers below refer to the step numbers on the diagnostic tables.
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This step determines if the scan tool is operating correctly.
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This step monitors the actively communicating modules with the scan tool's Diagnostic Circuit Check function. An active module is a module that is successfully communicating on the Class II 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; refer to Electrical Diagnosis for any unlisted modules.
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This step isolates the VCM by disconnecting all the other components on the Class II Serial Data circuit, refer to Electrical Diagnosis for the shared components on the Class II Serial Data circuit. After making repairs, it is necessary to clear DTCs from the modules that can communicate. Clearing DTCs will avoid future misdiagnosis.
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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.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and the Failure Records for reference. The control module's data is deleted once the Clear Info. function is used. Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Install the scan tool on a known good vehicle. Does the scan tool display the VCM data? | -- | |||
3 | Repair the scan tool or cables. Are the repairs complete? | -- | -- | |
4 |
Does the scan tool power up? | -- | ||
5 | Verify that the correct vehicle application was selected on the scan tool. Is the vehicle information correct? | -- | ||
Are any of the modules on the Serial Data Circuit communicating? | -- | |||
Does the scan tool display VCM data? | -- | Go to Electrical Diagnosis | ||
8 |
Is the test lamp illuminated? | -- | ||
9 | Probe the battery feed circuit (DLC pin 16) with a test lamp connected to ground Is the test lamp illuminated? | -- | ||
10 | Probe the ground circuit DLC pin 4) with a test lamp connected to the B+ terminal. Is the test lamp illuminated? | -- | ||
11 | Probe the ground circuit (DCL pin 5) with a test lamp connected to the B+ terminal. Is the test lamp illuminated? | -- | ||
Inspect the fuse that supplies power to the DLC. Is the fuse OPEN? | -- | |||
13 | Check for an open or poor connection in the Class II Serial Data circuit. Did you find a problem? | -- | ||
14 |
Is the action complete? | -- | -- | |
15 | Repair the open in the battery feed circuit. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
16 | Repair the open in the DLC ground circuit. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
17 | Repair the open or poor connection in the Class II Serial Data circuit. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
18 | Check for poor connections or improper mating at the DLC connector. Did you find a problem? | -- | Go to Diagnostic Aids | |
19 | Check for a poor connection of the Class II Serial Data circuit at the VCM and DLC harness connectors. Refer to Wiring Repairs . Is the action complete? | -- | ||
20 | Repair the short to ground in the Class II Serial Data circuit. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
21 | Repair the circuit as necessary. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
22 | Replace the VCM. Refer to VCM Replacement/Programming (Vehicle Control Module) . Is the action complete? | -- | -- | |
23 | Use the scan tool in order to display the Capture Info and the Review Capture Info functions. Are there any DTCs displayed? | -- | Go to the applicable DTC table | System OK |
