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.
Chart A6 - Oxygen (O2) Sensor Not Ready
The ECM provides a .45-volt reference to O2 sensor on circuit No. 412. When warm, a properly operating O2 sensor will drive the .45-volt reference lower (less than .45 volt) to indicate lean mixtures and higher (greater than .45 volt) to indicate a rich mixture.
When O2 sensor is cold (less than 200°C), the output voltage will be around 0.5 volt and the ECM will keep the system in open loop operation. When the ECM sees that the O2 sensor is varying from cold voltage of .45 volt and engine coolant value is greater than 85°C, it will send the system into closed loop operation. In closed loop operation, the ECM will adjust fuel delivery rate based upon oxygen sensor readings. CHART A6 should only be used when vehicle will NOT go into closed loop operation.
- With key on and oxygen sensor disconnected, BCM data parameter ED07 should read .45 volt (nominal). Lower or higher voltage indicates circuit problems.
- The ECM compares voltage on circuit No. 412 to ground voltage on circuit No. 413B. It is essential that oxygen sensor ground and ECM ground show good continuity (no voltage difference with engine running).
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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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