Got a Cobalt LS 2006, but for some reason the consume stands between 12.1 MPG (A/C off) and 13.0 MPG (A/C on). I'm really new at this, and I already replaced the oil, oil filter and spark plugs. Could this be a bad injector?, I'm not sure what engine it has, where can I check this?

 

You have an L61 engine. I would investigate the condition of the air filter and maf, also find a parts store to pull the check engine codes (some can be set without illumination).

 

If you have the engine codes pulled report back. for 12mpg either something seriously wrong or you forgot to release the e-brake.

 

Geez, that is real bad. Even my 4500 lb Vue with the old style L61 gets at worst 20 mpg.

 

Sounds like its running extremely rich. If you just got it, the tune may have been calibrated for some mods that are no longer on the vehicle.

Just for some insight, I had an 04 GTO about 12 years ago. I had it tuned for nitrous and my mileage went to 10mpg. It was doing 17mpg average. The tuner (no longer in business) did a terrible job and ended up going back to stock after I got a refund for their shitty tune.

 

With limited knowledge on the situation, it could be anything, but it sounds like your front O2 sensor (mounted in the header) has failed. That's the only time I've seen a car that terrible of mileage compared to what is expected.

 

Got the codes:
P0030 HO2S Heater Control Circuit Bank 1 Sensor 1
P0134 O2 Sensor Circuit No Activity Detected Bank 1 Sensor 1
P0135 O2 Sensor Heater Circuit Bank 1 Sensor 1
B2AAA Body (I guess this code is an error from the OBD?, there's no such thing as B2AAA)

Checked my O2 sensor, and guess what, it was disconnected, and the connector it was burned out, probably from exhaust heat.
Managed to clear the burned plastic from the connector to connect it again and scan again, and got these codes:
P0030 (HO2 sensor heater control circuit)
P0172 (system too rich)

I guess this means the O2 sensor is broken. Tried checking resistance on the two black wires (for code P0030), and there's open circuit.
Probably the last owner had issues with the O2, couldn't replace it, and he just decided to leave it unplugged.

Also, I opened the air intake, and there's some old sticky motor oil in there. What could this mean?

 

Some oil in the intake is normal from the pcv recirculation.

The o2 sensor being bad is why the fuel mileage is bad, I'm surprised it's not in engine power reduced mode.

 

Any idea how tightened should the O2 sensor be?, I don't wanna break something while replacing it

 

Snug then a turn or two tighter. Its all a feel thing IMO unless you are using a torque wrench.

 

Hand-tight plus 1/2-3/4 turn. It should be snug and require some force but it doesn't need to be crazy amounts of force (think similar to a spark plug, just a bit more).

 

Thank you guys, just one more last question. For how much could you rent the O2 sensor socket?, don't feel like buying a brand new for $15 in Amazon for a single use in a few years

 

A lot of places have the rent a tool program. You pay like 30 bucks and then when you return it they give it back to you. I have done this a lot of the years.

 

You shouldn't need an o2 socket if the wire connector is already burned off. Just use the box end of a wrench or a regular deep socket if you have one. Just install the new one with a wrench. I've removed and installed a number of o2 sensors and never used a special socket.

 

Thats how I have always done it, but some people are stiflers about using the "correct tool" and to spec.

 

Yeah I hear you. I actually wrote and posted my comment before yours came up. You posted while I was typing.

I think the special socket is really only necessary when the installed o2 sensor is seized in and you want to keep the wire intact. If the wire is fried you should be able to get a fully boxed-in tool on it no problem anyway.

 

I drove the car with the old "damaged" sensor for over 30 minutes, and it seems to be doing perfectly fine, from 12mpgh, went up to almost 40mpg. Probably some residue was left in the O2 sensor from not being used for probably years?
This is the damage the connector has (O2 sensor side)
I asked a mechanic (not a professional mechanic, he works on his house) on my city if it needed a replacement and asked him about the water leaking into the connection, and he said it was fine.
Not completely sure if it's really safe and I kind of agree with him since rainwater isn't really conductive, especially if we're talking about 12v.
What do you guys think?

 

If the connections are still good I would jam it full of dielectric grease, zip tie it together so it doesn't come disconnected, and send it.

 

100% agree. I once had to use an ex girlfriends hair tie to keep my fuel pump regulator together long enough for me to get her home and then me. In theory as long as the connections are clean you can and it works, zip tie it and go about your day.