DTC P0130: O2S1 Closed Loop Rationality: Description

O2S1 is an electrical source that responds to oxygen content in exhaust manifold. When sensor reaches approximately 600°F (316°C), it produces a voltage based on the difference in oxygen between atmosphere and exhaust gas. PCM sends a bias voltage (399-499 millivolts) on signal line, which is pulled up through high resistance. When O2S1 is cold, it produces no voltage and has extremely high internal resistance. Internal resistance of sensor is much more than the resistance of the bias pull-up resistor. However, when sensor heats up, it produces voltage that overrides bias voltage. This voltage is read by PCM to determine a rich/lean O2S1 signal used to adjust injector pulse width. Under normal conditions, low sensor voltage means high oxygen content/lean air/fuel mixture and vice versa. Normal sensor readings will fluctuate 10-1065 millivolts. DTC sets when O2S1 signal is not consistently fluctuating out or the 300-600 millivolt range necessary for closed loop fuel control.