QuestionQUESTION: If I needed to get a TCM and transmission, is the TCM inside the transmission, or is it an external part that would need to be bought separately?
ANSWER: The TCM (transmission control module) is a separate component and would need to be purchased separately.
I find it doubtful you'd need a TCM based on the codes you've reported in your other question.
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QUESTION: Would the problem be the overdrive, I have tried turning off the overdrive and I don't notice the problem with the transmission anymore, except for the high revving because it is off, and after driving long enough the Check Engine light eventually turned off. So does that mean that it is the problem?
AnswerYes, the problem is in one of the items necessary to engage 4th gear (overdrive). With overdrive off, the transmission will never shift into 4th gear, and the TCM will not see the problem.
Unlike a manual transmission which has a separate actual gear for each gear ratio, the automatic uses the same gears for numerous gear ratios, but controls which ones are fixed and which ones can turn to provide different gear ratios. So, the fact that the problem occurs in 4th gear doesn't make this a simple repair because we still must investigate what is worn and/or damaged.
