Hi, been awhile since ive been on here but I recently have been getting bank 1 lean codes. I found a small leak in exhaust from bank one at flange between the header and rear pipes. the exhaust was built at a muffler shop. the thing im wondering is could a small leak after the front 02 and b4 the rear 02 cause a lean code. I also found the header bolts had come loose, I know that's a no brainer. I tightened them but im thinking the gasket might be damaged and still hav a tiny leak. I got new gaskets and will change that side. she also gave me a code for excessive flow at egr, I found the dpfe sensor had a broken mounting hole so I put a spare on it instead of fixing the mounting hole, but im gonna blame the code on that sensor...

 

Exhaust leak after the upstream O2 wouldn't cause standard Lean code, it could cause Bank 1 Sensor 2 code, that's the downstream O2 sensor after the Cat converter
Header leaks will cause False Lean code on that bank
You can pull out a spark plug and check the tip, will be darker color if running Rich from a False Lean

DPFE sensors get water condensation inside because they sample exhaust pressure which is loaded with moisture, so tend to fail over time.
If idle is OK then EGR valve is not leaking.
Excessive flow could also be an EGR Solenoid problem, but long shot on that one, computer varies the Ground on this solenoid to open it a bit or alot, which in turn opens EGR Valve a bit or alot