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 acceleration by momentarily commanding valve on/open while monitoring engine MAP sensor signal. 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 fuel injector faults, misfire, idle speed, EGR pintle position, VSS, TP, IAT, MAP, ECT, CKP or MAF sensor related DTCs are set. DTC will also set when BARO is greater than 77 kPa, coolant temperature is greater than 176°F (80°C), engine speed at 900-1300 RPM, vehicle speed greater than 22.5 MPH, throttle is closed, EGR pintle position at less than one percent (valve closed), IAC position, MAP, engine RPM and vehicle speed steady or A/C clutch state and transmission state is unchanged. DTC will also set when 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.
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