Gen III Hybrid System Check light @ < 8000 miles My Gen III Model 3 California Prius check Hybrid System light (Yellow engine with the word Check under it) came on at 8800 miles in a heavy rain. No master warning light (Triangle with !). Checked under hood, no obvious water splashing. Retighten gas cap. Check Hybrid System light still on. Very late and wet Saturday night ... so I drove a mile or so home and it seemed normal. Is it safe to drive or should I have it towed to dealer? Seems to me a Hybrid System check light with < 10,000 miles is not a good sign about the cars reliability ... my old crappy Saturn waited 30k to break.
If the "check engine light" is not flashing, I'd drive mine. Flashing indicates a more serious issue. I've read here where a couple folks had Priuses with defective oxygen sensors, which were replaced under warranty; the other cause has been the loose gas cap, which you checked (but did you drive it after re-tightening the cap?). Even if your light goes out when you now start driving, the code will be stored in the ECU for some time.
Some code/warnings take 3 start/stop (power on/off) cycles to clear. Try that. If it does not clear, take it in. Don't worry about driving it.
In heavy rain, some G2 Prius have had an engine misfire problem when water leaked down from the cowl and dripped onto the engine valve cover, then seeping into a spark plug well. I wonder if your car had a similar problem? Do you notice any driveability problems? If not I would drive the car to the dealer. Pls let us know what DTC was logged and the dealer tech's diagnosis.
If you don't have a ScanGauge--buy one. Take it to one of the auto parts stores that read codes for free. If it is a BS code just have it cleared. If it is serious take it to the dealer. (If it was serious by now you'd know.)