Puzzling...!
FOr a start, it just tells where to have an inquisitive look if we have the error codes. Easy to get them:
jump together pins A and B of the diagnostic plug with a paperclip
www.avigex.ca/xport/plug.jpg
Turn key on
read the check engine light
It will flast 12 three times (one then 2 flashes) and then the codes, like 34 is 3 flshes then 4.
Keep a pencil handy
full details here:
www.avigex.ca/xport/readingdiagnostics.jpg
Meaning of codes here:
www.avigex.ca/xport/3800codes.jpg
Even if the CEL is not on, there may be stored codes anyway.
EGR will not kill the sparks.