What else can cause the Service Engine Soon light come on

[rescueme]

Please rescue my maxima.

My 99 maxima was diagnosed with EGR valve failure (P0400). The technican at Nissan dealer suggested to replace a new EGR valve and he was pretty firmed about that solution. However, 2 days later, the same Service Engine Soon light came on again.

I am very angry and sad to see the light came on again. My car only has 94k on it, and I still love this car very much.

Can any expert tell me some possible root causes that can trigger this EGR failure (P0400)?

[maxhopper]

Welcome to NICO.

It seems we have had a few members lately with similar problems. I believe theirs was caused by excess build up of carbon in the EGR tube itself.

[rescueme]

Excess build up of carbon in the EGR tube, that makes sense.

If excess build up of carbon in the EGR tube, do you know how much would that cost to fix the EGR tube?

Also, do you know any other areas can cause the SES light to come on?