I was having problems with my O2 sensor on my 99 Civic Si, so I swapped it out for a 4 wire universal today. When I put it in I got a CEL Code 41. All the wires are soldered. So I figured I would check the resistance across the stock O2 vs the replacement. What I found was that the stock O2 sensors had 13.5 Ohms of resistance across the heater wires and the universal replacement had 3.0 Ohms. Do you think that this may be what is causing the CEL 41? Any other thoughts?

 

Hmmm...I didn't think code 41 is for the O2 sensor heater....

 

"41 Primary Heated O2 Sensor Heater Open or short in Primary O2 sensor heater circuit "

 

Since none of the Honda specific guys have given you a reply, I will try from a Detroit Iron viewpoint.

I went to the shop and measured 3 universilish 4 wire sensors hanging out on the bench. Their heater measures 4.5 Ohms (Delco) number 1, 4.4 Ohms (Delco) number 2 and 3.6 OHms (NGK) sensor number 3. You can see there is variation in universilish sensors heaters when you factor in your 3 ohmer.

I have been thinking how you can fool the Honda ECM into thinking the sensor is OK and I have not come up with a technique that is cheaper than buying another sensor. The stock sensor at 13 ohms will pull about an amp cold, your universal at 3 ohms will pull about 4 amps cold. 400% more base current is probably too much for the ECM which has to sense heater condition for OBD2 diagnostics.

If I were designing the ECM I probably would allow +50% and -25% current from the median. Might even go to +100% and -50% as the limit. I would not accept +400% current as normal.

Good luck, maybee take your ohmeter with you to the parts store and try to find another. Did the counter person guarantee you it would work? You might be able to beg them to take it back. I would try to find a 8 ohm or more for your application. Note that as these heat up their resistance declines and the current goes down, but the OEM one will go down too. So that won't get you in the ballpark either.

Regards,
BigMoose