These Holley Commander 950 wideband replacement O2 sensors are the ultimate additions to any new or existing Commander 950 EFI system. They plug directly into all Commander 950 harnesses and accurately measure any air/fuel ratios between 10:1 and 20:1. This allows the engine tuner to read the air/fuel ratios in real time for extremely precise tuning. These sensors are designed for use with Holley controllers only. They are not intended to be replacement sensors for factory fuel injected vehicles.