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 VARIANT/TRIMSECTION 14 (ENGINE CONTROL SYSTEM & FUEL SYSTEM - 6.6L (LMM) - DTC P0700 TO DTC P2463)DTC P154ACIRCUIT/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 variant/trim than selected.
IMPORTANT:
You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
- Test the IAH feedback signal circuit for an open, a short to ground, or a short to voltage.
- If a condition is found, repair as necessary.
- Turn ON the ignition with a DMM measure between command two circuit terminal 3 and a good ground on the harness side of the connector for 0.78-1.1 Hz.
- If the DMM does not measure between 0.78-1.1 Hz ohms, replace the GPCM.
- Do not install the jumper wire between 12 volts and the command circuit for more the 20 seconds.
- Set the DMM to the 4V DC hertz scale.
- Turn OFF the ignition. Install a jumper wire between the IAH harness temperature signal circuit terminal 1 and the corresponding terminal on the IAH.
- Install a jumper wire between the IAH harness command two circuit terminal 3 and the corresponding terminal on the IAH.
- Supply 12 volts to terminal 2 on the IAH.
- Turn ON the ignition. Measure for 1 hertz on terminal 6 at the IAH.
- If 0.7-1.1 hertz is measured on terminal 6, replace the GPCM.
- If 0.7-1.1 hertz is not measured on terminal 6, replace the IAH.
IMPORTANT:
Set the DMM to the 4V DC hertz scale.
IMPORTANT:
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:
- • 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.