alright, so its my wife's 1997 nissan sentra, which was throwing a code for egr valve. didnt have time to fix it so i erased the code with my scantron and went for a smog check. I passed all the levels for O2, Co and whatever, but the guy said i failed the mil (engine light). He said he knew it was turned off. damn obd II. so now that the light is off, how do i know when i can take it back for a retest. i get a free retest in 15 days. what should i do now? thanks for any input everyone!

 

When you reset the ECU to clear an CEL/MIL/SES light, the internal status goes from ready to not-ready. You have to complete a "drive cycle" before the ECU determines that all is good and then it will go to "ready".

There is an official set of driving operations that define a "drive cycle" but it's probably a lot easier to just drive it around for a week or two before goes back to get the re-test.

The problem is that if you truly have an emissions problems, the CEL will probably come back on

 

well looks like you now have 15 days to fix the egr, which is usually very simple to just clean the EGR system out really well. or replace. the SES light will come back on in time if you dont fix the issue.

 

thanks guys, i think ill drive it for another week and see if it pops back on. in the meantime, ill see if i can clean or replace the egr valve/system or whatever i need to do. thanks again.