P0400 won't go off
 

I have an P0400 code that won't go off. I have changed the part out and had the pipes cleaned out. BTW the pipes was not clogged or dirty. The mechanic turn off the code. Told me to drive about 40 miles before they would inspect it for state inspection. The light came on at 20 miles. Checked it and the P0400 code came back up.

I don't know what to do. Does anyone have any idea what is going on?

Additional Information
*had a damaged neck filler that was replaced. The light was on before and after
*EGR valve and sensor was just put on.
* Clean out pipes
*all new belts
*new crank shaft pulley
* new alternator
* has all necessary fluids

One of your catalytic converters could be clogged.

Possible causes for the P0400 code are:

- EGR volume control valve stuck closed
- EGR passage clogged
- EGR temperature sensor and circuit
- Harness or connectors (EGR control valve circuit is open or shorted.)
- Exhaust gas leaks

ive had this code for A while, and noticed that if I put some fuel injector cleaner before A fill up it keeps it off for longer after A reset.