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 supplies a bias voltage (about 450 mV) on HO2S high and low signal circuits. Oxygen sensor voltage ranges from 10 mV when exhaust is lean to 1000 mV when exhaust is rich. PCM monitors and stores HO2S voltage information. PCM then evaluates voltage samples to determine amount of time HO2S voltage was out of range. PCM will compare stored HO2S voltage samples taken each sample period and determine if majority of samples are out of operating range. If PCM detects that voltage is out of bias range, DTC will set.
For duplication of DTC, ensure:
- DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 or P1258 are not set.
- Ignition voltage is 10-18 volts.
- ECT and IAT are less than 122°F (50°C) and are within 45°F (8°C) of each other at engine start-up.
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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.