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 during deceleration by momentarily commanding EGR valve on while monitoring engine MAP. PCM will illuminate MIL and store DTC P0401 if expected increase in MAP is not seen under certain conditions during deceleration.
Conditions required to set DTC are:
- No CKP, ECT, EGR pintle position, IAT, MAP, or TP sensor DTCs set.
- No misfire or VSS DTCs set.
- BARO is greater than 65 kPa.
- ECT greater than 180°F (80°C).
- Engine speed is 800-1500 RPM.
- IAC position steady.
- Vehicle speed greater than 25 MPH.
- 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.