Check Engine Light - o2 sensor

Hi there,

I am a new owner of a 2009 Chevy Aveo5 LT Hatchback 5 speed. I am a 21 year old female working as a paralegal in a busy law firm with a love for cars, however, I don't have much knowledge on how to diagnose problems... Here's my issue:

My engine light came on about a month ago, thermostat code, replaced the thermostat. Smell of fuel in oil, changed oil, kept oil in a Gatorade bottle, no separation of fuel and oil (not enough in it to separate) after oil change and months later, no fuel smell in oil. No check engine light.

This week, check engine light comes back on. Note, there are no noises, knocks, thumps, thuds, performance issues with this car ... I have not had one concern of this car acting strange at all... Nothing! So I get the car scanned today and two codes come up; Po138 and Po140 (o2 Sensors) .. but now I'm reading that 80% of the time, it isn't even your o2 sensor, even when the codes are pointing to o2 sensor... so what could it be!? Engine light went off on its own the other day and has not come back on yet.. however the codes are still reading..... keep in mind, no noises, no thuds, no knocks, no noises what so ever that makes me question this car.

Any ideas on what this is or what I should be looking for? Do i take it in and waste a bunch of money having mechanics look at it and tell me its an o2 sensor? Do I forget it because there is no noises and no issues with the car what so ever?

Any help or advice on this matter would be greatly appreciated.

Sincerely,
A young girl on a budget who does not want to spend thousands of dollars on an Aveo.....

Thank you all.

Hi kateredave09,

We're sorry to hear of these difficulties with your Aveo. I am not properly trained to offer technical assistance, but I will be glad to look further into this for you. Please send us a private message with your VIN if we can be of any assistance. Thank you.

Kristen A.
Chevrolet Customer Care

O2 sensors read a flow of air between two given points. You have an upstream and a downstream, these are your two points that will be read. O2 sensors mainly effect your fuel milage because it will either lean out your motor or enrich the fuel. When it enriches your fuel, you will have poor fuel mileage.

Some issues with sensors are when sensors sometimes just come on when carbon builds up and then you hit the accelerator and it blows off later. If you have an exhaust leak, it will set off the sensors as well and could just be the plugs but I would get the codes reset but write them down and hold onto those for later reference. If there is a real problem, it will come back on.