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 G2500, VAN CARGO, 6.6 6REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1801 (ENGINE CONTROLS AND FUEL - 4.4L - DTC P0010 TO DTC P0158)DTC P0068 OR P0121CIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6
Circuit/System Testing
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6SECTION Circuit/System Testing
WARNING: This page is about a different car, the 2009 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
You must perform the Circuit/System Verification before proceeding with the Circuit/System Testing.
- Inspect for the following conditions:
- Vacuum hoses for splits, leaks, and improper connections
- Air leaks at throttle body mounting area and intake manifold sealing surfaces
- A supercharger bypass valve that is binding or incorrectly adjusted-Refer to Supercharger Cleaning and Inspection .
- Inspect throttle body for dirt, debris, and coking. Refer to Throttle Body Inspection and Cleaning .
- If any of the above conditions are found, repair as necessary.
- Allow the engine to reach operating temperature. Observe the MAP Sensor Voltage parameter with a scan tool. Voltage should be greater than 0.8 volt and less than 4 volts.
- If greater than 4 volts or less than 0.8 volt, refer to DTC P0106 .
- Idle the engine. Observe the MAP Sensor kPa parameter with a scan tool. Increase the engine speed slowly and then back to idle. The MAP sensor kPa should change smoothly and gradually as engine speed is increased and returned to idle.
- If the MAP sensor kPa does not change, refer to DTC P0106 .
- Take a snapshot of the engine data list while performing the actions listed below. The mass airflow (MAF) sensor g/s should change smoothly and gradually as the engine is increased and returned to idle.
- Idle the engine.
- Increase the engine speed slowly to 3,000 RPM, then back to idle.
- Exit from the snapshot and review the data.
- Observe the Mass Air Flow (MAF) Sensor parameter frame by frame with a scan tool. The MAF sensor g/s should change smoothly and gradually as the engine speed is increased and is returned to idle.
- If the MAF sensor g/s does not change smoothly and gradually as the engine speed is increased and is returned to idle, refer to DTC P0101 or P1101 .
- Ignition ON, slowly depress the accelerator pedal to a WOT position, then slowly release the pedal while comparing the TP Sensor 1 and TP Sensor 2 parameters. The difference between the parameters should be less than 4 percent.
- If TP Sensor 1 and TP Sensor 2 parameters differ more than 4 percent, refer to DTC P0120, P0122, P0123, P0220, P0222, P0223, or P2135 .
- Ignition OFF, inspect the throttle body for the following conditions:
- Loose or damaged throttle blade
- Broken throttle shaft
- Any throttle body damage
- If any of these conditions exist, replace the throttle body assembly.
WARNING:
Turn OFF the ignition before inserting fingers into the throttle bore. Unexpected movement of the throttle blade could cause personal injury.
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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.