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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 up streams are responding perfect and oscillate beautifully.
Slightly shaky idle, at times and very intermittent occasionally extended long crank time on a hot soak for 5-10min's of sitting once warmed up.
Below is a link to a YouTube video I made of the issue. Recorded at idle.
"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? "
Thanks. No the P0157 for the low voltage O2 Sensor 2/2 hasn't returned since code was cleared. I've done about 70 miles of driving since I cleared the code. I need to check the Readiness Monitors to see if they have all completed. The biggest -concern is how the Long terms seam to run between +7 to +10 on both banks the higher on bank 2. I am unsure what acceptable Long term readings are for this 3.7 engine. I check everywhere with brake clean and Propane for vacuum leaks and couldn't find any. There is a small leak around the O-ring on the PCV valve, but when spraying it with brake clean it didn't affect the idle or the live data. I also wanted to mention that both down stream O2 sensor are pegged between +96% to +99% on their fuel trims. Also the fuel pressure seems fine too. 60PSI during prime and while running. Looses about 2.5 - 3 psi after prime key off after 15 mins. thanks
i didn't notice any exhaust leaks. The upstream O2 sensors are located after the only clamp that connects the headers to the cats and the downstreams don't have any connects after the cats. The cats are OEM and the ends are welded to the pipes the O2 sensors are located in. thanks
Acceptable LT+ST trims plus/minus 10. Looks like you are good.
Verify that the fuel trims stay normal from idle up to 80% engine load.
" I also wanted to mention that both down stream O2 sensor are pegged between +96% to +99% on their fuel trims."
Don't know the relevance of the these %
You can monitor the downstream O2 voltage should stay steady around .6-.8v at idle and move down to .1-.2v with quick throttle snap and after 15-20 seconds return to normal reading at idle.
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