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.
Circuit/System Testing
2009 Chevrolet Tahoe Base, 4.8 CSECTION Circuit/System Testing
WARNING: This page is about a different variant/trim than selected.
- You must perform the Circuit/System Verification first.
- Incorrect engine oil viscosity, aftermarket engine oil additives, or engine oil that is overdue for changing, can greatly affect the performance of the camshaft actuator.
- Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description .
- Ignition ON, verify the scan tool hood position parameter displays Open.
- If the hood position does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle for DTC P254F.
- Ignition OFF, disconnect the CMP actuator solenoid harness connector, X112.
- Test for less than 3 Ξ© between the low reference circuit terminal E and ground on the ECM side of the harness.
- If greater than 3 Ξ©, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
- Verify that a test lamp does not illuminate between the low reference circuit terminal E and the control circuit terminal D on the ECM side of the harness.
- If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
- Remove the test lamp.
- Command the CMP actuator from 0-20 degrees. Verify the scan tool CMP actuator ckt short to volts test status parameter is OK.
- If not the specified value, test the control circuit for a short tog round. If the circuit tests normal, replace the ECM.
- Install a 3A fused jumper wire between the control circuit terminal D and the low reference circuit terminal E on the ECM side of the harness. Command the CMP actuator to 20 degrees with a scan tool. Verify the scan tool CMP actuator ckt short to volts test status parameter is displaying Fault.
- If not the specified value, test the control circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
- Remove the water pump from the engine. Refer to Water Pump Removal .
- Inspect and test the remaining wire harness from X112 to the CMP solenoid for an open/high resistance or a short to ground.
- If all circuits test normal, test or replace the CMP actuator.
- If the CMP solenoid and the circuit test normal, refer to Camshaft Position Actuator Magnet Cleaning and Inspection and Camshaft Position Actuator Solenoid Valve Inspection (Off-Vehicle) .
NOTE:
RENDER: 1.0x
NO RELATED
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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.