Chart A6 - Oxygen Sensor Not Ready
The ECM provides a .45-volt reference to oxygen sensor on circuit No. 412. When warm, a properly operating oxygen sensor will drive the .45-volt reference lower (below .45 volts) to indicate lean mixtures and higher (above .45 volts) to indicate a rich mixture.
When oxygen sensor is cold (below 200°C), the output voltage will be around 0.5 volts and the ECM will keep the system in open loop operation. When the ECM sees that the oxygen sensor is varying from cold voltage of .45 volts and engine coolant value is above 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 code ED07 should read .45 volts (nominal). Lower or higher voltage indicates circuit problems.
- The ECM compares voltage on circuit No. 412 to ground voltage on circuit No. 413B. It's essential that the O2 sensor ground and the ECM ground show good continuity (no voltage difference with engine running).