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.
Code P043, Front Oxygen Sensor Rich Signal: Notes
PCM provides a .45-volt reference signal to oxygen sensor on circuit No. 412. When oxygen sensor temperature is less than 392°F (200°C), sensor signal voltage will be about .45 volt and PCM will keep system in open loop operation. When oxygen sensor temperature is greater than 392°F (200°C), sensor will begin to generate a signal voltage. In a rich environment, signal voltage will be greater than .45 volt. In a lean environment, signal voltage will be less than .45 volt. If PCM is in good control of air/fuel mixture, mixture will change from rich to lean rapidly (at least one change every 2 seconds).
When PCM sees oxygen sensor is generating a signal voltage (greater than .45 volt), it will send system into closed loop operation. In closed loop operation, PCM will adjust fuel delivery rate to engine based on oxygen sensor readings. Code P043 sets if oxygen sensor stays at rich voltage more than 45 seconds during test conditions. Code P043 also sets when oxygen sensor circuit fails or when air/fuel ratio is actually rich due to fuel control or emissions system fault.
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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.
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