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 MANUALSCHEVROLET2008CHEVY EXPRESS G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 503 (DATA COMMUNICATION SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESSCAN TOOL DOES NOT COMMUNICATE WITH LOW SPEED GMLAN DEVICECIRCUIT/SYSTEM TESTINGNOTES
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Circuit/System Testing: Notes
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Notes
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2009 GMC Savana Special, 2009 GMC Savana Camper Special, 2009 GMC Savana, 2009 Chevrolet RV Cutaway, and 2009 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
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.