What is the primary function of the SES light? What conditions or problems must be present in order to set this light off?

The reason I am asking is that my 2000 Maxima was involved in a flood in New Jersey long before I bought the car in Omaha, NE. The ECM was damaged and had to be replaced.

My SES light came on and I brought it to the dealership. What they told me is that when the ECM was replaced, it was replaced with one that had California standards meaning the emission control are a lot higher since there are more oxygen banks that the car checks for. The car puts out the emissions at the Federal standard. Therefore the SES light comes on because it is thinking that it is in California and the emissions are above standards. They told me they can replace the ECM with the correct one for $1000 and that was simply out of the questions.

Therefore, that brings me back to my original question. Due to the situation that I am in, it will be only a matter of time before the SES light comes back on since they reset the ECM. Can I correctly assume that when the light comes back on, it will be because of the emissions standard and not something else that is not oxygen sensor, cat, or emissions related? The past times when I brought the car in to have the MAF and to have the coils replacee, one of the error codes was emissions. Do I have a valid assumption?

Thanks.

 

I need to make a correction. My 2000 Maxima has California emission system and my ECU is Federal standard. What I need is a California standard ECU....