Exhaust Manifold leak vs P0402 code HELP

Can anyone tell me if a cracked exhaust manifold can trigger the P0402 code? the P0402 code is this.....
P0402 - system fault exhaust gas recirculation - too much flow on EGR
1) EGR valve stuck open
2) failed EGR pressure sensor, or valve or pressure sensor

.....or should i check the EGR valve and lines? if i need to check the valve or lines, what is the best do that? i know where they are located and ran seafoam through the motor. I am not positive the manifold is cracked but i can hear a "puffing" noise when driving and can not find a leak anywhere else so im assuming its a manifold leak but i do not smell any fumes or have other symptoms besides the "puffing". the manifold is covered by a heat shield and i cant remove the nuts of the shield because they are rusted on there pretty good. Or am i looking at two different problems?

thanks

 

does your engine run rough at idle? if no then your egr is not stuck open... check the egr modulator

 

no, my truck runs really well, i would never know anything is wrong if it wasnt for the CEL. where is the modulator?

 

its this little plastic circular thing right next to or close to the egr valve