I installed headers over the summer and have been dragging my feet in taking care of the CELs. MY inspection is due this week. Anyway, I had a P0153, so I replaced Bank 2 sensor 1 (blue one), and reset light. I also noticed a P0000 code but assumed it would clear itself. On my way to work this morning the light came back on. Checked it in the parking lot and the only code I have is P0000.
Any ideas?

 

The short story: I would just disconnect your battery overnight a hope your CEL light will clear. However, you can't go to your inspection the very next day, at least not here in CA. You need to wait about 2 weeks.

The long story: The ECM (p. EC-110) for 2000-2001 Max, states the following:

Once you have repaired the circuit or replaced a component, you need to run the engine in the same conditions and circumstances which resulted in the customer’s initial complaint. Perform the “DTC Confirmation Procedure” and confirm the normal code [DTC No. P0000] is detected. If the incident is still detected in the final check, perform STEP VI by using a different method from the previous one. Before returning the vehicle to the customer, be sure to erase the unnecessary (already fixed) (1st trip) DTC in ECM and TCM (Transmission control module). (Refer to EC-82.)

The above suggests that P0000 indicates things are "normal". However, perhaps your computer still remembers 1st trip DTC for your earlier P0153 because you did not erase it "properly" ....