DTC P0139-O2 Sensor 1/2 Slow Response: Notes

Fig 1: O2 Sensor 1/2 Circuit - Circuit Diagram

Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

For a complete wiring diagram, refer to appropriate SYSTEM WIRING DIAGRAMS article.

Theory of Operation 

The downstream O2 Sensor is located in the exhaust path behind the catalytic converter, is monitored for proper response to assure optimum catalytic converter efficiency. The downstream O2 response monitor is intended to diagnose a downstream O2 sensor that is not moving or stuck in a voltage window and to insure accurate information for catalyst monitor diagnosis. 

• When Monitored: 

  Vehicle is started and driven between 20 and 55 MPH with the Throttle open for a minimum of 120 seconds. Coolant greater than 70°C (158°F). Catalytic Converter Temp greater than 600°C (1112°F) and EVAP Purge is active. 

• Set Condition: 

  The oxygen sensor signal voltage switches less than 16 times from lean to rich within 20 seconds during monitoring. Two Trip Fault. Three good trips to turn off the MIL. 

Always perform the PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE before proceeding.