Upstream O2 Sensor Heater Failure

NAME OF CODE:
Upstream O2S Heater Failure

WHEN MONITORED:
With the ignition key OFF, after the engine cools down.

SET CONDITION:
No sensor output signal is received when the Powertrain Control Module (PCM) powers up the sensor heater.

THEORY OF OPERATION:
The upstream oxygen sensor is a voltage generating device. The PCM receives exhaust gas information from this O2 sensor. The sensor detects exhaust gas content by a galvanic reaction within the sensor that produces a voltage. After measuring the amount of oxygen in the exhaust gases, the upstream oxygen sensor tells the PCM how well its output signal is controlling the air/fuel ratio. Variations in the signals from the O2 sensor serve as air/fuel ratio indicators. Changes in the sensor signal occur because the air/fuel ratio is constantly changing. When oxygen content is low (rich mixture), the voltage signal will be approximately 1 volt. When oxygen content is high (lean mixture), the voltage signal will be low, approximately 0.1 volt. The heater element helps the O2 sensor quickly reach a normal and steady operating temperature, which is required for proper emission control.

POSSIBLE CAUSES:
- Open heater element circuit
- O2 sensor failure