Silverado Classic 2500 4WD V8-6.6L DSL Turbo (2007)
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An open in a high speed GMLAN serial data circuit between the DLC and the first splice. This open will cause no communication with the
scan tool, and will not effect the module communication on the vehicle.
CIRCUIT/SYSTEM TESTING
Automatic Transmission
1. Ignition OFF, disconnect the harness connector of the GPCM.
2. Ignition ON, with a scan tool attempt to communicate with the ECM/PCM. Communication should not be available.
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If the ECM/PCM communicates, replace the GPCM.
3. Disconnect the ECM/PCM. Ignition ON, with a scan tool attempt to communicate with the TCM. Communication should not be available.
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If the TCM communicates, replace the ECM/PCM.
4. All 3 modules disconnected, test for less than 5 ohms of resistance between the DLC and the TCM on both high speed GMLAN serial data
circuits.
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If greater than 5 ohms, repair the data circuit for open/high resistance between the DLC and the first splice.
5. All 3 modules disconnected, test for infinite resistance between all 4 of the high speed GMLAN serial data (+) and (-) circuits of the TCM.
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If less than infinite resistance, repair the short between the serial data circuits.
6. Ignition on and all 3 modules disconnected, test for less than 1.0 volt between the high speed GMLAN serial data circuits of the TCM and ground.
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If greater than 1.0 volt, repair the serial data circuit of the TCM for a short to voltage.
7. All 3 modules disconnected, test for infinite resistance between the high speed GMLAN serial data circuits of the TCM and ground.
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If less than infinite resistance, repair the serial data circuits for a short to ground.
8. If all circuits test normal, replace the TCM.
Manual Transmission
1. Ignition OFF, disconnect the harness connector of the GPCM.
2. Ignition ON, with a scan tool attempt to communicate with the ECM/PCM. Communication should not be available.
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If the ECM/PCM communicates, replace the GPCM.
3. Test for less than 5 Ohms of resistance between the DLC and the ECM/PCM on both high speed GMLAN serial data circuits.
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If greater than 5 Ohms, repair the data circuit for open/high resistance between the DLC and the first splice.
4. Both modules disconnected, test for infinite resistance between the high speed GMLAN serial data (+) and (-) circuits of the DLC.
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If less than infinite resistance, repair the short between the serial data circuits.
5. Ignition on and both modules disconnected, test for less than 1.0 volt between the high speed GMLAN serial data circuits of the DLC and ground.
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If greater than 1.0 volt, repair the serial data circuit for a short to voltage.
6. Both modules disconnected, test for infinite resistance between the high speed GMLAN serial data circuits of the DLC and ground.
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If less than infinite resistance, repair the serial data circuits for a short to ground.
7. If all circuits test normal, replace the ECM/PCM.
REPAIR INSTRUCTIONS
Perform the Diagnostic Repair Verification after completing the repair. See: Testing and Inspection/Diagnostic Trouble Code Tests and Associated
Procedures/Verification Tests and Procedures
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Control Module References for module replacement, setup, and programming See: Testing and Inspection/Programming and Relearning
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GMLAN Wiring Repairs
Scan Tool Does Not Power Up
SCAN TOOL DOES NOT POWER UP
CIRCUIT DESCRIPTION
The data link connector (DLC) is a standardized 16 cavity connector. Connector design and location is dictated by an industry wide standard, and is
required to provide the following:
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Scan tool power battery positive voltage at terminal 16
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Scan tool power ground at terminal 4
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Common signal ground at terminal 5
The scan tool will power up with the ignition OFF. Some modules however, will not communicate unless the ignition is ON and the power mode
master (PMM) module sends the appropriate power mode message.
TEST DESCRIPTION
