sauer04

I'm not very knowledgeable about cars, so any guidance would be great. The malfunction indicator light came on today and the malfunction was diagnosed as a P1166 (Heated oxygen sensor/ heater circuit malfunction or Air/fuel ratio/heater system electrical malfunction). The vehicle is running the same and nothing else seems out of the ordinary.

What should be done and how soon should it taken care of? What price range should I expect for the repair?

Splaturn

Your oxygen sensor is going bad.

You need to replace it. Total out the door at a dealerships is over 400 bucks (parts and labor) parts alone will cost you about 250. It's a ceramic type o2 sensor, and if you're thinking about going with bosch, it'll fail in about 80 miles. Bosch itself isn't a terrible brand, but on the crv's it's really finnicky. NGK/NTK are your best bets for replacements.
#24410 for the rear and #24666 for the front. I'd venture to say the primary is bad, but it could very well just be a connection problem, so start there first.

phootbag

I would diagnose the heater circuit before replacing any parts. Heaters usually fail because they are subjected to the most extreme conditions. The heater is not always at fault. There can be various wiring problems outside the sensor that can cause this DTC to set. Diagnosis may be cheaper than replacing a good sensor.