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 - O2 Sensor (Rich Fuel Mixture): Notes
The ECM supplies a voltage of approximately .45 volt between terminals No. B2 and B3. Oxygen sensor varies voltage from one volt (rich exhaust) to .1 volt (lean exhaust). The sensor acts like an open circuit and produces no voltage when exhaust temperature is less than 680°F (360°C). An open sensor circuit or cold sensor causes open loop operation.
- A Code 44 is set when oxygen sensor signal voltage on circuit No. B3 remains greater than .1 volt, TPS is greater than 10 percent, Codes 21A, 21B or 33A and 33B are not set, engine has been running for at least 2 minutes, system is operating in closed loop, oxygen sensor voltage is less than .35 and greater than .55 volt, engine is at normal operating temperature, integrator mode is not at 128 counts and all conditions are present for 50 seconds.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
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.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
No obligation. See pricing before you book.