Pontiac Repair: Diagnostic code questions..., upper intake manifold, mr saunders

Question
Mr. Puccio,
Mr. Saunders,
I have a 2001 Buick LeSabre Custom (3.8 engine), and my "Service Engine Soon" light is on.  I hooked up a scanner and got the following diagnostic codes:
P0128
P0404
P1404
I know that P0128 has to do the with the thermostat, and the other two relate to the EGR valve.
My question:  If I replace the thermostat, and replace the EGR valve...will that fix both codes?  (Assuming, of course, there is not something much more serious way down deep in the engine.)  The car runs fine, but I'd like to stay ahead of problems.
Any suggestions, advice you can offer is greatly appreciated.
Warm regards,
David Gardner

Answer
Hi David:

your correct on both codes. BUT this may be low on coolant and that will cause the 128 code as well as a thermostat. that engine has issues with the upper intake manifold plenium leaking coolany and also lower intake gaskets leak as well. So make sure it's not low on coolant if it's not just replace the thermostat. if it's low then look at the 2 things I said for a leak. good luck :)