OBD-II code · Emissions / Engine
The reverse of P0401: too much exhaust is recirculating. A valve stuck open gives rough idle, hard starting and a car that smells like a bus depot — and on some engines the same code appears when a MAP sensor simply lies about pressure.
New EGR valve. If the actual culprit was the $40 MAP sensor feeding it bad math, the rough idle is still there after the invoice clears.
Typical guess-and-swap cost: $400–$800 (valve) when the real fault was a $40 sensor
Compare commanded EGR duty against the pressure-change signature on live data, then verify the MAP sensor against a known-good reference. Confirm whether the valve physically sticks before condemning it.
Mobile service in Canyon Lake, San Antonio & Austin. Written report with root cause — see a sample.