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 13, Oxygen Sensor Circuit Open Circuit
The ECM supplies approximately .45 volt between ECM terminals 3 and 20. If reading is taken with a 10-megohm DVOM, reading may be as low as .32 volt. The O2 sensor produces a varying voltage as engine reaches normal operating temperature. Voltage will vary from .10-1.0 volt. The O2 sensor does not produce a voltage until sensor reaches 600°F (316°C). When sensor is less than this temperature, an "Open Loop" condition exists. Code 13 will set with engine at normal operating temperature, at least 5 minutes of engine run time after engine start and part throttle, O2 sensor signal steady between .35-.55 volt, throttle is off idle and all conditions present for approximately 60 seconds. Computer system will not go into "Closed Loop" when these conditions exist.
- This determines if O2 sensor is at fault or if ECM and wiring are faulty.
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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.