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 187 (DATA COMMUNICATION SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESSCAN TOOL DOES NOT COMMUNICATE WITH HIGH SPEED GMLAN DEVICECIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Circuit/System Testing
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Circuit/System Testing
WARNING: This page is about a different car, the 2008 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
- With a scan tool verify that communication is not available for all high speed serial data modules.
- If any high speed module communicates and any DTC beginning with a U exists, refer to Diagnostic Trouble Code (DTC) List - Vehicle
- If any high speed module communicates and no DTC beginning with a U exists, refer to DTC U0100-U0299 or U2105-U2199
- Ignition OFF, Test for less than 5 ohms of resistance between the DLC ground circuit terminal 5 and ground.
- If greater then the specified range, test the circuit for an open/high resistance.
- Ignition OFF, Test for less than 5 ohms of resistance between each IPM ground circuit and ground.
- If greater then the specified range, test the circuit for an open/high resistance.
- Ignition OFF, disconnect the harness connector of the IPM.
- Ignition ON, test for battery voltage between each voltage input circuit of the IPM and ground.
- If less than battery voltage, test each voltage output circuit of the IPM for a short to ground, and each voltage input circuit of the IPM for a short to ground or and open/high resistance. If the circuits test normal, replace the faulty module.
- Ignition OFF, Disconnect the appropriate harness connector at the ECM.
- RPO LY7 - X2
- RPO LH2 and LC3 - X3
- Attempt to communicate with the Distance Sensing Control Module, communication should not be available.
- If communication is established, replace the ECM.
- Ignition OFF, Disconnect the harness connector at the TCM.
- Attempt to communicate with the Distance Sensing Control Module, communication should not be available.
- If communication is established, test the serial data circuits for a short between them, short to ground or a short to voltage between the TCM and ECM. If the circuits test normal, replace the TCM.
- Ignition OFF, Disconnect the Harness connector at the EBCM.
- Attempt to communicate with the Distance Sensing Control Module, communication should not be available.
- If communication is established, test the serial data circuits for a short between them, short to ground or a short to voltage between the EBCM and the TCM. If the circuits test normal, replace the EBCM.
- Ignition OFF, Disconnect the harness connector at the Distance Sensing Control Module.
- Attempt to communicate with the VCIM, communication should not be available.
- If communication is established, replace the Distance Sensing Control Module.
- Ignition OFF, Disconnect the harness connector at the VCIM.
- Attempt to communicate with the ESC module, communication should not be available.
- If communication is established, test the serial data circuits for a short between them, short to ground or a short to voltage between the VCIM and Distance Sensing Control Module, and the VCIM and TCM. If the circuits test normal, replace the VCIM.
- Ignition OFF, Disconnect the harness connector at the ESC module.
- Attempt to communicate with the IPM, communication should not be available.
- If communication is established, test the serial data circuits for a short between them, short to ground or a short to voltage between the ESC module and the VCIM. If the circuit tests normal, replace the ESC.
- Ignition OFF, Disconnect theX3 harness connector at the IPM.
- Ignition OFF, Test for infinite resistance between the serial data circuits of IPM terminal 4 and ground, and between IPM terminal 5 and ground.
- If less than specified, test the circuit for a short to ground.
- Ignition ON, test for less than 1 volt between the serial data circuits of IPM terminal 4 and ground, and between IPM terminal 5 and ground.
- If greater than specified, test the circuit for a short to voltage
- Ignition OFF, test for infinite resistance between the serial data circuits of IPM terminal 4 terminal 5.
- If less than specified, test the serial data circuits for a short between the circuits.
- If the circuits test normal, replace the IPM.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.