I just installed a new radiator.

Driving around, no problem w/ the car at all. But when I initially put the car in the "on" position (engine is off), after a few seconds, the CEL flashes me, then stays solid again (back to normal). When I turn on the engine, everything is fine. No CEL, nothing.
Any clues? I tried the brake reset and the reset button holding reset, stills comes back on. Do I need to do some driving cycles?

Again, note, no CELs when the engine is running. Only when the engine is off and in "on" position.

Thanx!