After my check engine light came on due to a delayed o2 sensor reading, I took it to the dealership and they replaced the o2 sensor. The next day, the same light came on again, so I went to an auto shop to see what they would diagnose. They reported that it is the oxygen sensor. He told me that I might have to drive for a few days for it to go away or that they had installed it incorrectly. The code was P0139 and I have 78,000 miles. What is your assessment of this and how can I fix the problem?
The code P0139 is for the O2 sensor before the catalyst. The code is for when the engine control module is testing the O2 sensor it cuts the fuel to see if the O2 sensor detects a lean condition within 5 seconds. If it does not set the code. This can be caused by the evaporative vent solenoid (EVAP) allowing fuel vapor into the engine from the fuel tank when it was commanded closed for the O2 sensor test. If excessive fuel vapor leaks past the EVAP, then the engine will get excessive fuel vapor causing the O2 to detect it as a problem since it is staying rich too long. Have the EVAP vent valve checked for leaks and replace as needed. If you need help with this, a certified technician from YourMechanic can come to your home or office to diagnose the Check Engine Light and make the appropriate fixes for your 2011 Suzuki SX4.
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