I have about 160,000 miles on the 2.4 NA. Got a CEL with P0037 "HO2S Bank 1 Sen 2 Heater Circuit Low". I can't even clear the error code. It's as if as long as the ignition is on to read/clear the code that it immediately re-records the code - so I can't really clear the code even though the engine isn't running (but of course the ignition is on. I disconnected the O2 sensor lead at the disconnect which is anchored to the cross member just forward of the Cat. I observed 4 wires - blu, white, blk, blk. I assume the blu and wht wires are paired with whichever blk is neighboring in the plug (not diagonally). Anyway, regardless of which two pins I probe for resistance through the sensor, I get infinite resistance - all 4 appear to be totally open circuit. The wires all appear to be in good shape - no worn spots or chafing, etc. No external damage to the sensor. Everything looks nice and clean with no corrosion. So it would appear I've got an issue in the sensor.

But what seems a bit odd to me: I don't know which wire pair powers the sensor heater and which two carry the voltage signal back to the brain. But is it not odd that both circuits would go open at the same time? Or could it be that, say, the heater circuit has been open for a long time and finally the O2 sensor pair have finally gone open and triggered the CEL - or vise versa?

The car idles/runs/accelerates perfectly fine.

Also, can anyone verify that the NTK (NGK) #25619 is the proper sensor for a 2003 V70 2.4 NA (49 state if that matters these days)? Mine has about a 19" lead or 21" if you count the square connector.

As usual, thanks in advance.