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
After achieving "closed loop" fuel control, a commanded air/fuel ratio of 14.7:1, RPM between 1500-3200 and airflow between 7-25 grams per second, PCM will continuously monitor the front O2S signal for 100 seconds. During this time, the PCM counts the number of rich-to-lean and lean-to-rich switches. Voltage reading should be less than 300 mV and greater than 600 mV, to be considered a switch. The number of switches along with the time to achieve these switches are used to calculate the average response time to perform each switch. This information is also used to calculate if the proper ratio of the switches is correct.
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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.