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 and adds amount of time it took to complete all transitions.
With this information, an average time for all transitions can be determined. PCM then divides rich-to-lean average by lean-to-rich average to obtain a ratio. If HO2S ratio is not within range, DTC will set.
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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.