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.
Code P0401, EGR Flow Test Failure - "S" & "T" Series 4.3L (VIN W): Notes
Control module tests exhaust gas recirculation valve by momentarily commanding valve on while monitoring engine RPM. Control module will illuminate Malfunction Indicator Light (MIL) and store Code P0401 if expected drop is not seen for a calibrated number of tests.
- Ensures EGR valve is allowing EGR flow and control module is capable of controlling EGR valve.
- Ensures control circuit is not shorted to ground.
- Ensures control circuit is not open and that control module quad-driver for circuit is properly functioning.
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.