Upstream O2 Sensor Shorted to Voltage
Name of Code:Upstream 02 Sensor Shorted to Voltage
When Monitored:
With the engine running for more than 2 minutes and coolant temperature above 170°F.
Set Condition:
The upstream oxygen sensor signal voltage is above 1.2 volts.
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 signals are controlling the air/fuel ratio. Variations in the signal from this 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 mill be approximately 1 volt. When oxygen content is high (lean mixture), the voltage signal will be low, approximately 0.1 volt.
Possible Causes:
- Sensor output wire shorted to another circuit
- Dirt/moisture/grease causing voltage tracking in connector
- O2 sensor failure
- Powertrain control module failure
- Connector terminals
- Connector wires