I googled the P203E fault code for s&g and it seems there are only a few causes:

Reductant level sensor defective
Wrong fluid in DEF storage tank
Broken wire or harness causing intermittent electrical connections
Electrical short

I'm guessing a new level sensor and you're on your way. But that's just a guess.

"We live in a time when intelligent people are being silenced so that stupid people won't be offended".