What is Code p1406?

This code indicates a problem with the EGR valve's pintle position. The EGR Valve's pintle could just be stuck in which case the problem could be fixed by cleaning the EGR valve.

If the EGR valve is electronically controlled or cleaning the valve does not fix the problem, you will most likely have to replace the EGR Valve.

Keep in mind that the EGR valve relies on inputs from other sensors to determine the pintle position. If one of these other sensors is not operating correctly, it could be giving you a false P1406 error code.