90 EX, can't lose a code 41
 

There was a NGK O2 sensor in my Accord EX (F22A4). It started throwing a code 41. I replaced it with a Bosch. Code 41 comes back.

I compared heater circuit resistance from NGK (19 ohms) to Bosch (5 ohms), and spliced a 14 ohm 1W resistor in so the Bosch matched. Code 41 comes back.

I replaced with Denso O2 sensor (plugged in, didn't bother to install). Code 41 comes back.

There is battery voltage at the O2 sensor harness.

To clear the ECU I am pulling the upper right fuse in the fuse box, but not pulling the battery cable. The radio clears so I think I'm doing it right.

At this point I can only think that the ECU is bad. Does anyone have another idea?

I have never had so much trouble with an O2 sensor.

How fast will it code? If it codes fast take a close look at all you connectors and wires before replacing the ecm. Search for a pin out on the ecm on your car unplug ever thing all 4 wires should have less then .01 ohms.

It throws the code within 3 seconds of starting the engine.

I'll check all the wires, but I don't know what could have happened. It threw the code 41 originally while I was on a long highway drive, and hasn't gone away since.