Auto Tranny Error Code

[DonC]

My 1990 535 (130k) has started flashing the 'Check Engine' light at stop lights. Doesn't do it all the time however. Checked the codes with my Peake reader and got a 'Torque Converter Clutch' message. Any ideas what this implies? I've wanted to do a 5-speed swap (but not now!) - maybe this will force me to do it.

Thanks!
DonC