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i had this happen on my ls400, same motor as your sc400 obviously. my problem was egr temperature, code 71 i believe. Do a diagnostic check and tell us what engine code/s show up. If its anything like my LS u just connect two pinouts on the diagnostic port under the dash. But i could be wrong, maybe someone else can chime in on this.
My light has been on for a couple of months now . I took it to a shop and they said it was that my egr's are going bad. But i've been riding it out, the check engine and trac off light has been turning off here and there.