So I’ve encountered a problem. So I had a check engine light come on about a month ago and it came back with a p0172 code. The next day the light turned off for about a month and it recently turned back on. Now I hear a rattling or pinging sound coming from under the car? Could it be a problem with my EGR valve, catalytic converter, or a sensor? I’m not sure what it could be exactly

 

The code means Engine running Rich Bank 1.

 

Could the rear upper (bank 1) Cat come apart and that is what you are hearing "rattle"?

 

I took it to a mechanic and they told me the heat shield came loose and that they would put clamps on it. As for the CEL code, he said it’s weird for a TL with 94,000 miles to run rich

 

EGR or o2 sensor.

 

I’ve gotten 3 o2 sensors changed already

 

Run some SeaFoam to clean out the system. Otherwise look into cleaning the EGR