# Oxygen sensor monitor not ready



## slacorte (Aug 14, 2016)

Checked 2017 Sentra SV for I/M readiness last month and found the Oxygen Sensor monitor was not ready. No DTC's were set. Replaced battery (due to weak load test), and did oil change and antifreeze replacement. Also replaced air filter and disconnected battery, let vehicle sit for hours, and then reconnected battery. I have been doing drive cycles (to the best of my ability - hard to drive in Phx area at 55mph), and after 250 miles, ALL BUT the oxygen sensor monitor report as completed. All other monitors completed as expected within 50 miles (Catalyst, EGR, EVAP, O2S Heater, etc). Upstream AFR sensor PID data looks normal (fluctuating around 1.0 lambda, voltage around 2.25). Downstream O2 sensor is new NTK and fluctuates around .600. The STFT is around +1%, LTFT is around -4% at idle speed. Cleaned MAF and values at idle are around .25 lb/min, and around 10 lb/min at 3000 rpm. Coolant temp between 180 and 200 F. Car runs fine, idle is good, and no carbon detected in tailpipe. Still no DTC's.

I appreciate any suggestions. Any thoughts of what could be preventing the monitor from completing.

Thank you very much for your help. God bless!


----------



## VStar650CL (Nov 12, 2020)

Many times P-DTC's from group B won't clear until you drive both pattern B and pattern D in succession, with a key-cycle in between. Also, some aftermarket scanners won't indicate "first trip" or "pending" DTC's. Pending induction DTC's like P0101 can prevent the cat and O2 SRT's from completing, even though the DTC is still pending and hasn't turned on the MIL.


----------



## slacorte (Aug 14, 2016)

Thanks for the info. The vehicle has not had any confirmed or pending DTC set. I will try another drive cycle but this time I will record at least the highway travel for MAF, STFT, LTFT and the upstream O2 sensor data. I will post anything I find out. Thanks.


----------

