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I have 7th gen Civic (EU) with 1.6 l engine. I've replaced upstream O2 sensor after heating element failed in the old one (error P0135 if I remember correctly). It worked fine for a while, but I rarely used the car and mainly took it easy. After a few longer trips check engine light started to appear, always with error P0131. I tried to replicate the problem and it only happens when the engine is worked hard for longer periods, eg. when overtaking or going uphill. If I don't reset it using ODB reader, it usually goes off the next day or so. I checked the wiring and it's intact. Idling is smooth and steady. The car did not seem to lose power. Fuel economy is pretty much the same. No strange smells from exhaust. There was a leak in rear muffler, which I replaced, but it did not change the behaviour. I've also topped up engine oil as it was slightly below correct level on the dipstick - again with no change. What should I check next? Thanks.

 
Rep Power: 222

What brand was the new sensor?

 
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Lemark, if my memory serves me right (it was some time last year).

 
Rep Power: 366

hondas have a history of not working well with aftermarket sensors
denso or ntk are oem

 
Rep Power: 222

Fail needs to be the oe sensor, either Denso or ntk.

 
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Interesting. As these sensors are not rocket science, what's the mechanics of this issue? If there are no other problems with the engine, will running with Lemark sensor and occasionally getting P0131 affect it in longer(ish) term? Anyway, the original Denso sensor was 234000-7003, which is no longer available. I looked up compatibility charts and Lemark one I bought was supposed to work. What's the current Denso equivalent?

 
Rep Power: 222

Tried here? https://www.densoautoparts.com/find-my-part.aspx
Or does rockauto work in your country?

 
Rep Power: 222

Honda's are just very picky with sensors/electronics, needs to be the original equipment