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 328 (DATA COMMUNICATION SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC U1818CIRCUIT/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 does not describe the selected car, but rather 8 other vehicles, including the 2008 GMC Yukon XL, 2008 GMC Yukon, 2008 Chevrolet Tahoe, 2008 Chevrolet Suburban, and 2008 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
- Ignition OFF, disconnect harness connector X1 of the APM and the EBCM.
- Test for less than 1.0 ohm between the APM and the EBCM on the following circuit terminals.
- PTLAN + APM terminal 5 and EBCM terminal 33
- PTLAN - APM terminal 1 and EBCM terminal 21
- If greater than the specified range, test the circuit for an open/high resistance.
- Ignition OFF, disconnect harness connector X1 of the SDGM.
- Test for less than 1.0 ohm between the EBCM and the SDGM on the following circuit terminals.
- PTLAN + EBCM terminal 34 and SDGM terminal 13
- PTLAN - EBCM terminal 22 and SDGM terminal 11
- If greater than the specified range, test the circuit for an open/high resistance.
- If the circuits test normal, replace the SDGM.
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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.