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Nissan Sentra 2.0, Usual waveform signal of downstream o2 sensor

posted Apr 11, 2016 17:41:39 by JuanGabrielFlorezMoreno
Hello, I have a question about the waveform of the downstream sensor on a nissan sentra 2L. I am viewing the signal on Torque Pro app and my upstream is around 450mV until idle and my downstream get oscillating (min. 100mv, max 900 mv) when warmup and rpms are over 3000, thats ok. But the frequency of the oscillation of the downstream sensor is very slow (one cycle in 5 seconds), its means that i have to change the sensor? or i have another problem?, I don,t have MIL light on, but my mileage is bad on the city and good on highway. Thanks for your support.
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2 replies
Tyler said Apr 12, 2016 01:41:11
Hey Juan! Just for my information, what year is your Sentra?

The downstream sensor switching slowly isn't necessarily an issue, especially on systems with upstream air/fuel ratio sensors (which I believe yours uses). Really, with a warmed up and functioning catalyst, the downstream sensor should stay at a steady voltage while cruising. Switching during warmup and cold operation isn't unusual, as the catalyst hasn't 'lit off' yet.

If your main concern is fuel economy, then I'd suggest looking at your fuel trims at idle and during a test drive. Apply the standard +/- 10% rule, and let us know if you find any issues!
JuanGabrielFlorezMoreno said Apr 12, 2016 02:45:44
Hello tyler, my Sentra is 2010. Checking the fuel trims after an ECU reset:

on idle the initial value of LTFT was 14,8 when warmed up was 10,9 and STFT around to 0,

revving without load the LTFT was around to 0 and STFT around to 10.

Then released the pedal and the values return to LTFT=+-10 STFT=+-0.

I don't have idea if that good or bad,

Tomorrow I will take a graphic for more details under driving conditions, thanks a lot for your anwers.
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