Check engine light with P0031 code do not go away after replacing oxygen sensor
 

Hey guys,

when I bought my NB 2002 miata 3 months ago it had a check engine light on, which was about the pre catalytic oxygen sensor. More specifically I could see in ODB reader the following codes:
-P0031: HO2S Heater Control Circuit Low Bank 1 Sensor 1 (Powertrain, Generic)
-P0171: System Too Lean Bank 1 (Powertrain, Generic)

After doing some test to the heating element resistance I decided to buy a new one. The guy supplied me with a universal one and.O had to connect the wires on my own. I put the sensor in, connected the wires temporarily and erased the codes. The car drove without any issue for a week. After that, the check engine light came on again with only the P0031 code.

I thought my wiring connection would not have holded and went to have a look. Indeed the wiring had failed; so I decided to put them together permanently. I have done that for some time now and the best I can get is turn the code off and not come back for 1-2 days. Then it's back again.

Then I started looking into the voltage and I can see that the 12V go through the power wires. And the resistance seems to be measurable. Goes pretty high when I put the multimeter on and eventually settles down.

What I have noticed through my ODB software though is that that sensor 1 does not show ouput voltage while the 2nd ones does. Which I think this is the symptom of the problem. I have measured again, seen voltage and didn't have the check engine light on that day.

Any suggestions? Any help would be most welcome! Thanks

I'd start with an application-specific o2 sensor to start. You may be having issues from the universal one you wired in.

Does it really make that much of a difference? Like the application specific ones are designed properly for the specific engine / ECU ?

What I didn't mention is that the universal one i got is Denso, so it's a reputable one. The guy didn't have the application specific one which costs roughly 20 EUR more but he said it's pretty normal to get the universal one.