Oxygen heater sensor diagnostic routine

An oxygen sensor heater diagnostic method, for diagnosing the condition of an oxygen sensor having a heater and used in an automobile engine to intercept the exhaust gases from the engine and provide a measurement of the fuel-air mixture, comprising the steps of:

• turning off the heater;
• preventing the exhaust gas of the engine from heating the sensor;
• measuring a voltage V1 when the sensor is connected through a large pull-up resistor to a first source of voltage and a voltage V2 when the sensor is connected through a small pull-up resistor to a second source of voltage to determine an initial delta reference voltage, that is, the difference between V1 and V2, which is proportional to the sensor internal resistance;
• repeatedly measuring a first series of delta voltages until the delta voltage exceeds the initial delta reference voltage by a predetermined level;
• turning the heater on;
• measuring a second series of delta voltages;
• comparing the magnitudes of the delta voltages in the second series of delta voltages;
• and
• determining the heater is functioning if the delta voltages of the second series of delta voltages are decreasing and determining the heater is not functioning if they are not.

A sensor diagnostic method for diagnosing the condition of an oxygen sensor having a heater, comprising the steps of:

• allowing the sensor to cool;
• energizing the heater;
• repeatedly measuring a voltage V1 when the sensor is connected through a large pull-up resistor to a first source of voltage and a voltage V2 when the sensor is additionally connected for a short period of time through a small pull-up resistor to a second source of voltage;
• determining a series of delta reference voltages by subtracting the repeated voltages of V1 and V2, and
• monitoring the magnitude of the delta reference voltages to determine whether they are decreasing, as an indication that the heater of the sensor is operating properly.