Oxygen Sensor Heater Monitor

CAUTION: If there is an oxygen sensor (O2S) shorted to voltage Diagnostic Trouble Code (DTC), as well as a O2S heater DTC, the O2S fault must be repaired first. After the O2S fault is repaired, verify that the heater circuit is operating correctly

DESCRIPTION
Effective control of exhaust emissions is achieved by an oxygen feedback system. The most important element of the feedback system is the O2S. The 02S is located in the exhaust path. Once it reaches operating temperature 300° to 350°C (572° to 662°F), the sensor generates a voltage that is inversely proportional to the amount of oxygen in the exhaust. The information obtained by the sensor is used to calculate the fuel injector pulse width. This maintains a 14.7 to 1 Air Fuel (A/F) ratio. At this mixture ratio, the catalyst works best to remove hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxide (NOx) from the exhaust.

OPERATION
The voltage readings taken from the 02S sensor are very temperature sensitive. The readings are not accurate below 300°C. Heating of the 02S sensor is done to allow the engine controller to shift to closed loop control as soon as possible. The heating element used to heat the 02S sensor must be tested to ensure that it is heating the sensor properly.

The O2S sensor circuit is monitored for a drop in voltage. The sensor output is used to test the heater by isolating the effect of the heater element on the 02S sensor output voltage from the other effects.