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 45, Oxygen Sensor Circuit Rich Exhaust Indicated: Notes
The ECM supplies a voltage of approximately .43 volt between ECM terminals D6 and D7 (if measurement is taken with a 10-megohm DVOM, reading may be as low as .32 volt). The O2 sensor varies the voltage within a range of about one volt if exhaust is rich and down to about .10 volt if exhaust is lean. When sensor temperature is less than 600°F (316°C), the sensor acts like an open circuit and will not produce voltage. An open sensor circuit or cold sensor causes an open loop condition.
- Code 45 sets when O2 sensor signal voltage is fixed above .75 volt (750 mV), TPS is more than 3 percent, Codes 21 or 33 are not present, system is in closed loop, coolant temperature is less than 158°F (70°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.