Upstream O2 Sensor Heater Failure

Name of Code:
Upstream O2 Sensor Heater Failure

When Monitored:
With the Ignition key off, after the engine cools down.

Set Condition:
No sensor output signal is received when the 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 02 sensor quickly reach a normal and steady operating temperature. which is required for proper emission control.

Possible Causes:
- Open heater element circuit
- 02 sensor failure
- PCM failure
- Dirt/moisture/grease inside connector
- 02 sensor heater wires
- ASD relay failure