check engine light on--help pls.

My Honda Civid 2001 has its check engine light one again recently.
The car seems to run perfectly fine as before.
Checked error code at Autozone: P0740 TCC not engaged
Possible causes:
1. Open or short circuit condition
2. Poor electric connection
3. Failed TCC system

This is not the first time that the check engine light was on. Actually a
few years ago same thing happened for the first time. I went to dealer,
payed 100$ for diagnostics and was told me to change transmission for 3600$.
I did not change. After a month or so, the light went off by itself.
After that, the light went on and off intermittently for a few times. I
realized it could be due to the reason that the lid for the gas tank was not
closed properly, because everytime the light went on or went off, it
happened after I filled gas.

However this time, it just happened from nowhere. I am a little scared.
Can somebody tell me what to do? I am afraid of going to the dealers
because they will just charge me the diagnositic fee and then ask me to
change the transmission.

Many many thanks.