How to determine which O2 sensor is bad
 

The check engine light is on, I checked with a scanner and the code is listed below, it does not tell me which one of the two sensors is bad. How can I determine that, I would appreciate any help

Code: P1166 HO2S11 Heater Circuit Fault.

Engine Info:
2000 Honda Accord EX 4 Cyl
F23A4

Heated O2 Sensor 1 bank 1

Its the one upstream of the catalytic converter.

O2 Sensor,
 

Thank you for the quick response, is that the one on the exhaust manifold in the engine compartment?

Yes.

There are some resistance tests that you can do on that sensor to see if the circuit is open. You can download a shop manual from the online manuals link in the DIY section to get the proper procedures.

Unplug the sensor & look for 2 same-color (black?) wires from the sensor itself. Measure resistance between them. Normally should be 10-40 ohms, but I think you have the ULEV engine so I'm not sure if the preheater is the same wattage.

But normally if a heater fails, it'll go to open-circuit.

If the heater resistance is OK, the next thing is to check for power at those 2 wires coming from the car. One should get battery voltage as soon as the engine's running, the other will be near-ground. The ground side goes thru the ECU, so it may have some resistance to a good body-ground.