Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Circuit Description
Oxygen Sensor (O2S) produces a voltage that varies between 300-600 millivolts under normal operating conditions. PCM monitors this voltage and determines if exhaust is lean or rich. If voltage input at PCM is about 100 millivolts, exhaust is lean. If voltage input at PCM is about 900 millivolts, exhaust is rich. PCM constantly monitors O2S signal during closed loop operation and compensates for a lean or rich condition by adjusting injector pulse width as necessary.
DTC will set if system is in closed loop less than 40 percent of the total time and the following conditions have been met:
- TP angle between 10-40 percent.
- ECT greater than 149°F (65°C).
- Engine speed between 1200-3400 RPM.
- Engine running at least 140 seconds.
- DTCs P0107, P0108, P0117, P0118, P0122, P0123, P0131, P0132, P0134, P0201, P0202, P0203, P0204, P0300, P0325, P0336, P0440, P0442, P0446, P0502, P0601, P0602, P1441, P1621 and P1640 are not set.
When DTC sets, MIL will illuminate after 2 consecutive ignition cycles in which diagnostic runs with active fault. PCM will record operating conditions at time of failure and store information in freeze frame buffer.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.