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 12 (ENGINE CONTROL SYSTEM & FUEL SYSTEM - 6.6L (LMM) - DTC P0300 TO DTC P0699)DTC P040FDIAGNOSTIC AIDS
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Diagnostic Aids
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Diagnostic Aids
WARNING: This page is about a different variant/trim than selected.
- A slight to moderate resistance in either signal or low reference circuit can widen the spread between the two EGR temperature sensors and cause this DTC to set.
- An EGR temperature sensor that is skewed lower at various ambient temperatures, due to more resistance than is normal, can widen the spread between the two sensors and cause this DTC to set. Measure and record the resistance of both EGR temperature sensors 1 and 2 at ambient temperature. Compare those measurements to the Temperature Versus Resistance (EGR Temperature Sensors) or Temperature Versus Resistance (Fuel Temperature Sensor) or Temperature Versus Resistance (IAT Sensor 1) or Temperature Versus Resistance (ECT Sensors) or Temperature Versus Resistance (IAT Sensor 2) or Temperature Versus Resistance (EGT Sensors) .
- Inspect both EGR temperature sensors terminals for corrosion and for poor connections. It is very important that a thorough inspection of the wiring and connectors be performed. Failure to fully inspect wiring and connectors may result in misdiagnosis, causing part replacement with reappearance of the malfunction.
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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.