I have a 2003 Honda CR-V EX, with 39,000 miles. The check engine light came on recently. I read the OBD II codes and got P1166 and P0134. The generic P0134 indicates the O2 sensor upstream of the catalyst. The Honda proprietary code (P1166) may indicate something to do with "Primary HO2S Heater System", from browsing the internet. I'm not sure what this second thing is. I don't want to go buy an expensive 02 sensor for P0134 and have it really caused by the other problem. I also think it unusual that two different systems would go bad simultaneously, so I wonder if they're related. I checked fuses and found no problems. Can anyone shed some light on this pair of codes and what really is the underlying problem?

I've also heard that after-market O2 sensors for Honda don't work right. Will I need to get the expensive OEM part?

The two codes can be very related. Many O2 sensors have an internal electrical heating element to help accelerate the warmup of the sensor while it is still in "open loop" mode. After it is fully warmed and all sensors are working in "closed loop", the O2 sensor regulates the air/fuel mixture. If your heater in the sensor has failed or is not getting voltage, you would get the codes that you have. 39K miles is pretty quick for a O2 sensor to quit from normal old age, but I suppose anything is possible.

You can check the connections at the cat/con under the car to see if all is physically Ok. If you can ID which lead is which, you can check that the leads to the heater are getting 12V. I don't have access to my service manual right now, so I can't look up the color coding. Can't say for certain if the wiring on my 05 is the same as on your year, either.

I also have read that many aftermarket O2 sensors are not quite compatible with certain cars. I did have success on a VW, though, with an aftermarket unit that I had to splice the OEM connector onto.

Good Luck