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
VCM test Exhaust Gas Recirculation (EGR) valve by momentarily commanding valve on while monitoring engine MAP. VCM will illuminate MIL and store DTC P0401 if expected increase is not seen under certain conditions during deceleration.
Conditions for setting DTC:
- No ECT, EGR, EVAP, IAC, IAT, MAP, TP or VSS sensor DTCs set.
- No transmission DTCs set.
- Change in IAC less than 8 counts.
- ECT greater than 172°F (78°C).
- Vehicle speed greater than 27 MPH.
- BARO greater than 70 kPa.
- A/C clutch status unchanged.
- Transmission locked/unlocked status unchanged.
- No misfire DTC set.
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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.