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P1404 is described as EGR valve pintle stuck open, which in most cases is a false alarm. Possible reason (very likely) for the false P1404 code is that the plastic piston of the EGR valve position instrument (LVDT?) wears over time and starts reading a different position at valve closed than what it was when the EGR valve was first installed. When the car was built and the computer circuits energized for the first time the computer learned the EGR valve closed position signal from the valve position instrument that is built on top of the valve itself. Over time, when the instrument wears, a slightly different signal is sent to the computer and when it differs enough from the 'Valve Closed Signal', that the computer had learned, the trouble code P1404 is set and the 'Service Engine Soon' light comes on.
Replacing the EGR valve with a new one does not necessarily fix this problem because the 'Valve Closed Signal' between valves is slightly different and it is just pure luck if your new valve would give a 'Valve Closed Signal' close enough to your original valve'* signal not to set the trouble code. This is why the new EGR valve 'Valve Closed Signal' must be re-learned by the computer.
So, what this all means is that if the P1404 is a false code meaning that the valve pintle is not stuck open, then new 'Valve Closed Signal' can be re-learned by the computer using the old valve.
The fix goes like this:
1. Disconnect the wire harness from the EGR valve.
2. Turn key ON and erase the trouble code(*) from the car'* computer AND TURN KEY OFF IMMEDIATELY WHEN THE SCANNER SAYS CODES HAVE BEEN ERASED. DO NOT TURN KEY ON BEFORE YOU RE-CONNECT EGR WIRE HARNESS.
3. Re-connect EGR wire harness and your problem should be fixed.
I believe erasing codes with wire harness disconnected and turning the key OFF right after P1404 code has been erased re-sets the 'Valve Close Position' reading in the computer and triggers computer to re-learn position next time the key is turned ON.