Working on diagnosing an evap/emission/fuel system problem on my Toyota 2003 Corolla. More on that in this question.
On 3/2, I saw a mechanic use his handheld OBD to read a code P0420. On 3/12, without any code resets, I got my Ozzy OBD reader and read code P0440 using Torque.
I understand that sometimes later codes change because of faults in earlier codes, but I don't believe I've ever seen the primary and only fault change. Is this normal variance that I (because of my inexperience) just haven't seen, or is it indicative of something deeper?
- 3/15: After a reset drive cycle, the new code read is P0446.
- 3/16: After a reset drive cycle, the new code read is P0420. Have confirmed cat failure, so this code seems correct.