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 MANUALSCHEVROLET2006SUBURBAN C2500, 6.0 UREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1620 (IMMOBILIZER SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC P254FCIRCUIT/SYSTEM TESTING
2006 Chevrolet Suburban C2500, 6.0 U
Circuit/System Testing
2006 Chevrolet Suburban C2500, 6.0 USECTION Circuit/System Testing
WARNING: This page is about a different car, the 2009 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
- Ignition OFF, disconnect the harness connector at the hood ajar switch.
- Ignition OFF, test for less than 10 ohms between the ground circuit terminal A and ground.
- If greater than the specified range, test the ground circuit for an open/high resistance.
- Ignition ON, test for 10.0-12.5 volts between the signal circuit terminal B and ground.
- If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the SGCM.
- If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the SGCM.
- Ignition ON, test for 10.0-12.5 volts between the signal circuit terminal C and ground.
- If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the SGCM.
- If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the SGCM.
- Ignition OFF, disconnect the harness connector at the hood ajar switch.
- Ignition ON, observe the scan tool SGCM Hood Position parameter. With the hood open, the Hood Position parameter should read Open. With the hood closed, the Hood Position parameter should read Closed.
- If the parameter does not change between the specified values, test or replace the hood ajar switch.
- Observe the scan tool ECM Hood Position parameter. With the hood open, the Hood Position parameter should read Open. With the hood closed, the Hood Position parameter should read Closed.
- If the parameter does not change between the specified values, replace the ECM.
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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.