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 593 (DATA COMMUNICATION SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC U0123CIRCUIT/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 2010 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
- Ignition OFF, disconnect the harness connector at the yaw rate/lateral acceleration sensor.
- Ignition OFF for 60 seconds, test for less than 5 ohms between the low reference circuit terminal 1 and ground.
- If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the yaw rate/lateral acceleration sensor.
- Ignition ON, test for ignition voltage between the ignition voltage circuit terminal 4 and ground.
- If not within the specified range, test the ignition voltage circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the yaw rate/lateral acceleration sensor.
- Ignition OFF, disconnect the harness connector X3 at the SCM, and X3 at the EBCM.
- Ignition ON, test for less than 1 volt between the following terminal listed below and ground.
- SCM serial data circuit terminal 52
- SCM serial data circuit terminal 72
- If greater than the specified value, test the appropriate serial data circuit for a short to voltage. If the circuit tests normal, replace the yaw rate/lateral acceleration sensor.
- Ignition OFF, test for infinite resistance between the following terminal listed below and ground.
- SCM serial data circuit terminal 52
- SCM serial data circuit terminal 72
- If not the specified value, test the appropriate serial data circuit for a short to ground. If the circuit tests normal, test or replace the yaw rate/lateral acceleration sensor
- Test for less than 2 ohms between the appropriate serial data circuit terminals listed below.
- Serial data circuit terminal 52 at the SCM harness connector and terminal 2 at the yaw rate/lateral acceleration sensor harness connector.
- Serial data circuit terminal 72 at the SCM harness connector and terminal 3 at the yaw rate/lateral acceleration sensor harness connector.
- If greater than the specified range, test the appropriate serial data circuit for an open/high resistance. If the circuit tests normal, replace the yaw rate/lateral acceleration sensor.
- Test for infinite resistance between the SCM serial data circuit terminal 52 and the SCM serial data circuit terminal 72.
- If not the specified value, repair the serial data circuits for a short together.
- If all circuits test normal, replace the SCM.
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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.