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 Description
PCM tests Exhaust Gas Recirculation (EGR) valve by momentarily commanding valve on while monitoring engine MAP. PCM will illuminate MIL and store DTC P0401 if expected increase is not seen under certain conditions during deceleration. Conditions required to set DTC are:
- No ECT, IAT, MAP, or TP sensor DTCs set.
- No misfire, linear EGR (pintle position) or vehicle speed sensor DTCs set.
- BARO is greater than 10 psi (0.7 kg/cm2 ).
- ECT greater than 180°F (80°C).
- Vehicle speed greater than 25 MPH.
- Engine speed is 800-1400 RPM.
- IAC position steady.
- TP angle less than one percent.
- Commanded state of A/C relay is steady.
- MAP changes monitored during EGR flow test indicate insufficient EGR flow.
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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.