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 44, O2 Sensor CKT/Lean Exhaust Indicated
ECM supplies a voltage of approximately .43 volt between ECM terminals D6 and D7. If voltage is measured with a 10-megohm DVOM, reading may be as low as .32 volt. The O2 sensor varies voltage within range of .1 volt (lean exhaust) to 1 volt (rich exhaust). When sensor temperature is less than 600°F (316°C), the sensor acts like an open circuit and will not produce voltage. A cold sensor, or open sensor circuit, causes open Loop condition.
- Code 44 is set when O2 sensor signal voltage is fixed above .280 mV, TPS is more than 3 percent, Codes 21 and 33 are not present, system is in closed loop, coolant temperature is less than 155°F (68°C), and integrator count is not at 128.
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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.