A drain/fill/drain/fill type of flush is harmless and wont hurt your seals or cause any premature failures. Yearly changes should keep your fluid in very good condition with 30K being the max safe mileage. Some of the 'power flushes' have been reported here and on other boards to result in failures within a few weeks. I dunno if it messes up seals or whatever, but just a word of warning for what it's worth. As mentioned previously, if the CEL was flashing, the code can be read because the computer saves a copy of the error codes for a long time.
