97 Civic EX

Got ONLY a 41 CEL - O2 Sensor Heater Circuit

I'm not too familiar with ODB2 cars so I figured I'd post to be safe.

Did a couple of searches but didn't get any real positive responses.

ODB2 O2 sensors have heater's built in?
If SO, should I be changing just the primary O2 sensor(The one up top) or ??????

BTW, nothing has been done to this car..
It's a friends car, totally stock, automatic, daily driver with like 160K on it.

 

Heated O2 sensors started in mid-'80s, long before OBD-2. Other than that, you're about right...

The primary sensor is the one upstream of the cat, often in the exhaust manifold. Sometimes it's in the pipe just before the cat.

Unplug it, measure resistance between the 2 same-color (black?) wires. On most Hondas it should be 15 to 40 ohms, with no continuity from either wire to ground. If not, replace the sensor.

If the sensor heater is OK by that check, then look for cut wires, worn-off insulation, loose connectors, & stuff like that.