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
PCM monitors Heated Oxygen Sensor (HO2S) activity for 100 seconds. During this period, PCM counts number of times that HO2S switches from rich-to-lean and lean-to-rich. When PCM determines that HO2S does not switch enough times, DTC will set.
A lean-to-rich switch is determined when HO2S voltages changes from less than 300 mV to greater than 600 mV. A rich-to-lean switch is determined when HO2S voltage changes greater than 600 mV to less than 300 mV. DTC will set when PCM determines that within 100 seconds the HO2S lean-to-rich switches are less than 10 and rich-to-lean switches are less than 10.
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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.