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I have a 2004 Jeep Liberty, 3.7L, 115,450miles. I got a code P0157 O2 bank 2 sensor 2 low voltage at open loop, high idle shortly after a cold start. The freeze frame data in my scan tool wouldn’t provide fuel trims or O2 voltages when the lite was tripped. Since then I cleared the code and notice the long term bank 1 was at +10 and bank 2 was at +14. Short terms are fluctuating around zero +/- 1. My diagnoses is it running lean and more lean on bank 2. I cleared the PCM to restart the fuel trim adapt and now the long terms are bank 1 +6 and bank 2 +8 and the short terms still properly fluctuating around zero.The one thing I noticed and I’m not familiar with is the down stream O2 sensors stay flat lined down the center at .80v for a long time until warmed up and then only fluctuate while accelerating or decelerating. The cats were replaced at 90k by the dealer according to the car fax service history. Is this normal for the O2 downstream sensors to not fluctuate unless change in RPM and if no, is it possible there are incorrect or failing O2 sensors installed? Bank 2 sensor 2 is less responsive thank the bank 1 sensor 2. The upstreams are responding perfect and oscillate beautifully.
Slightly shaky idle, at times and very intermittent occasionally extended long crank time on a hot soak for 5-10 mins of sitting once warmed up.
Below is a link to a YouTube video I made of the issue. Recorded at idle.
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Is that video is from the scantool or are you connected directly to the oxygen sensor?
When the fuel system is in open loop it does not use the feedback from the O2 sensor. Maybe that is why the scantool is showing 0.8 volts constantly. When the temperature rises and the fuel system goes into closed loop you should see the downstream sensor stay pretty constant above 0.65 volts or so. I don’t know Jeeps but my Kia’s downstream sensors usually fluctuate from 0.65 to 0.7 volts. Of course when you accelerate or decelerate the downstream sensor will go temporarily lean or rich. I am not sure if this helps or is what you were asking.
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