Q: P 0400 error

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I recently had a P0400 OBD-II error on my son's 2009 Ford Escape. I replaced the electronically controlled EGR valve and the problem was fixed for about one week. However, the check engine light has come back on and I am getting a P0400 flow error again. I am certain it is not the EGR valve since it is brand new. Any suggestions for why the issue would have resolved for a week and then returned?? Thank you for any input.

My car has 110000 miles.
My car has an automatic transmission.

Diagnostic Trouble Code P0400 can set if the EGR valve is faulty but other causes for code are a break in the vacuum line to the EGR valve, a faulty EGR temperature sensor, or carbon deposits and blockages in the EGR tubes to the intake manifold. Those possible causes of the code setting should be carefully ruled out. If you want these possibilities evaluated by a certified Mechanic, dispatched by YourMechanic right to your location, please request an EGR system diagnostic/inspection and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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