I previously posted here: https://priuschat.com/threads/o2-sensor-monitor-never-completes.210963 A few months ago, I reset the ECM and resumed driving the vehicle in efforts to get the monitors to complete. After several hundreds of miles of driving following this point, the oxygen sensor monitor has not yet completed. Under the On-Board Diagnostic Monitors tab of OBD Auto Doctor, the "$8F - Manufacturer Defined Test" has not yet completed. I researched what this meant but was unsuccessful. Does anyone knows what this refers to and how I can get it to complete? Prius-monitor-status by david95376 posted Jun 12, 2020 at 7:51 PM As a site note, I noticed that the battery charges and discharges abnormally quickly under the Energy Monitor screen of the vehicle. I understand that this is a possible indicator of a need for a hybrid battery replacement, but can this affect the oxygen sensor monitor completion?
Once when visiting a smog shop, Torque reported one of the tests hadn't completed after driving many miles, yet the vehicle still passed. If you're still using non-OEM sensors, this could be the issue and they can be tested. Have you checked the spark plugs or fuel trim(s) lately? A mini-vci cable and a copy of techstream can show you the conditions that were met when the DTC(s) are logged. What are the current OBD2 codes (DTCs) ?
Last year, a non-OEM oxygen sensor was installed, causing a DTC to appear due to incorrect voltage values. It was soon replaced with a used OEM sensor, which did not cause any problems. During the past hundreds of miles, no codes were set, but the battery died over the weekend, so I will drive it a few hundreds of miles again to see if any DTCs appear. I ran Techstream today, which revealed that the short term fuel trim were within the range of -10% to 10%. I am planning to check the spark plugs soon, when I am free after attending graduation celebrations this week.
So you were too cheap to buy a Denso o2 sensor from RockAuto, or Denso direct, then got a used sensor from somewhere? Are we talking the rear O2 sensor, or the front Air/Fuel sensor? There is a difference. You actually bought a used Air/Fuel sensor (the thing you call a front O2 sensor) and figured everything would be OK? Try an OEM Denso 234-9056. It's 105.79 plus shipping from RockAuto. I understand it's more than the 5 bucks you spent at Pick and Pull but it will solve your problems.
