Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2009CHEVY EXPRESS G2500, VAN CARGO, 4.8 CREPAIR AND DIAGNOSISENGINE PERFORMANCETESTING & DIAGNOSISDATA COMMUNICATION SYSTEMDIAGNOSTIC INFORMATION AND PROCEDURESSCAN TOOL DOES NOT COMMUNICATE WITH LOW SPEED GMLAN DEVICECIRCUIT/SYSTEM TESTINGNOTES
2009 Chevrolet Chevy Express G2500, Van Cargo, 4.8 C
Circuit/System Testing: Notes
2009 Chevrolet Chevy Express G2500, Van Cargo, 4.8 CSECTION Notes
NOTE:
Use the schematic to identify the following:
- Control modules the vehicle is equipped with
- Control module locations on the low speed GMLAN serial data circuit
- The low speed GMLAN serial data circuit terminals for each control module
- Attempt to communicate with all control modules on the low speed GMLAN serial data circuit, refer to Data Link ReferencesΒ . Communications should not be available with two or more control modules on the low speed GMLAN serial data circuit.
- If only one control module is not communicating, diagnose that control module only, refer to DTC U0100-U0299Β .
- If one or more control modules are communicating but not all, refer to Testing the Serial Data Circuit for an Open/High ResistanceΒ .
- Disconnect the scan tool from the DLC. The following tests will be done at the DLC connector.
- All access doors closed, ignition OFF for 60 seconds, test for less than 10 Ξ© between the ground circuit terminal 5 and ground.
- If greater than the specified range, test the ground circuit for an open/high resistance.
- Ignition ON, test for less than 4.5 V between the serial data circuit terminal 1 and ground.
- If greater than the specified range, test the serial data circuit for a short to voltage, refer to Testing the Serial Data Circuit for a Short to VoltageΒ .
- Ignition OFF for 60 seconds, test for greater than 100 Ξ© between the serial data circuit terminal 1 and ground.
- If less than the specified range, test the serial data circuit for a short to ground, refer to Testing the Serial Data Circuits for a Short to groundΒ .
- Disconnect the appropriate harness connector at the JX 200 splice pack.
- Test for less than 2 Ξ© between the DLC serial data circuit terminal 1 and the JX200 splice pack terminal 1.
- If greater than the specified range, test the serial data circuit for an open/high resistance. If the circuits test normal, replace the splice pack.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- β’ You smell fuel, burning insulation, or see smoke.
- β’ Brakes feel soft, pull hard to one side, or make grinding noises.
- β’ The engine overheats, stalls repeatedly, or misfires under load.
- β’ You are missing required tools, torque specs, or safe lifting equipment.
- β’ You are not confident in the next step or safety outcome.