98 savana p1780 code

the "service engine soon" light came on.
I checked the code and is p1780.
but I didn't notice any problem on the transmission.
any help?

You mean p1870, common code, usually caused by the pcm recognizing a slippage condition during tcc lock up, caused by a worn valve body bore for the tcc valve, the pcm boosts pressure to compensate.