I don't know why either, but you can find out why. Check out the manual at
http://www.iequus.com/assets/manuals/3173_ICCR_E_14JAN03.pdf
and read the introductory stuff at the front, up through page 17 of the PDF
(it's a quick read). Your car is covered on page 19 of the PDF, near the
bottom, and the codes are listed on page 24. The pages from 21 through 24
are important stuff too. Yours doesn't require the "tool" they talk about,
but it's just a shorting plug anyway. I bought that and the manual in
paperback form for $35 US before I found out it was on line :-(

Once you get the code(s) we can help you more.

Mike