13 Oxygen Sensor Circuit - Open/Not Ready
The oxygen (02) sensor consists of a zirconia electrolyte between two platinum plates. When the sensor reaches approximately 318°C (600°F) it becomes an electrical source that responds to the oxygen content in the exhaust. The PCM produces a bias voltage of approximately 470 millivolts on the oxygen sensor circuit. When the sensor is cold its internal resistance is extremely high, therefore, the PCM recognizes the bias as an open circuit. As the sensor warms up, the internal resistance decreases. When the sensor reaches approximately 318°C (600°F), it starts producing a voltage based on the oxygen content in the exhaust stream. This voltage is used by the PCM to determine a rich or lean signal and adjust the fuel mixture accordingly.
- The 02 voltage is inactive (not reading outside 350-550 mV) for 20 seconds when the following exist:
- The engine is at normal operating temperature (the CTS reads over 60°C [140°F]).
- The engine has been running at least one minute.
- The TPS reads over 6.5% (the engine is off idle).
- Code 21 and 22 are not present (TPS codes).
- The PCM will not go into closed loop if a Code 13 is set.
- When attempting to diagnose an intermittent problem, use the Scan Tool to review supplemental diagnostic information.
- The supplemental data can be used to duplicate a problem. Select MALF History from Scan Tool EC menu.
- Voltage can be read on wires without disconnecting any connectors.
- Check the tightness of the female terminal grip with a spare male terminal.
- Normal Scan Tool readings in closed loop will show the oxygen sensor voltage varying between 10 mV and 999 mV .
- A code 13 can be set if the vehicle runs out of fuel or stalls while the vehicle is in motion.
- Code 13 can set or cause false oxygen sensor readings if the oxygen sensor ground becomes loose. Refer to PCM and Engine Grounds.