2000 outback check engine light on all the time, changed front o2 sensor, changed fuel cap, unplugged battery, and none turn this light off.\r\n any suggestion?

Sounds as if your fuel pressure regulator has gone bad. You didn't say what codes the O2 sensors tripped. I would change the regulator before chasing down the sensor code. I hope this helps. Take care.

4 most common causes of engine light on
-oxygen (O2) sensor
-loose fuel cap
-very cold weather affecting airflow under the hood.
-in need of oil change.
check these. As for fuel cap, make sure you crank it around a few times after each fill...very cold weather, you just have to wait. Save your engine with an oil change regularly, and get your mechanic to show you where the O2 sensor is on your vehicle. May just need the contacts cleaned.

broken evap line/port on fuel pump. Or leaking fuel pump o-ring
check the EVAP canister it is right next to fuel filter could be pcm needs update to fix false codes. Here is a old hillbilly trick that may help put saliva on the seal of gas cap when you fill up every time that may work for you.

Did you disconnect your battery for a few minutes. This will clear the fuel cap and other code as well. Basically what that code means is the your O2 sensor has detected a lean burning condition. Not sure if you know but the O2 sensor is located in your exhaust pipe. You have 2 before the catalytic converters (1 before each converter as you have 2 of them). You also have one O2 sensor after the converter. The O2 sensor detects how much fuel, air and emissions is going through the exhaust. Then the O2 sensor send a signal to the vehicles computer which tells the fuel injectors how long to stay open as the have a pulse and turn on and off delivering only a certain amout of fuel. Since it says it detected a lean condition, that could mean a number of things such as a bad O2 sensor, a bad fuel injector or simply a vacuum leak. Since the fuel cap light came on I would start by looking for a vacuum leak. Look around the engine for any old, rotten or loose vacuum lines. There are also a few "vapor" lines in the rear, under the vehicle around the gas tank. Check those as well. Also check you PVC valve. That's where I would start. I don't know it all and never will but have been a mechanic for over 25 years and happen to be a Ford specialist. In a nut shell the O2 sensor is not detecting enough gas and to much air which like I said is more then likely a vacuum leak since the other light is on. In most cases if it was a fuel injector not producing enough gas you would notice a performance problem like a miss or hesitation. After you check for leaks and correct anything disconnect your battery and drive it a few time and see if the code and light(s) come back on. If they don't then you have corrected the problem. If the check engine light comes back on you may be looking at a bad O2 sensor. Below is a picture of your exhaust and I have marked which O2 sensor is having the problem. Also below is a picture of what the O2 sensor looks like. It is screwed into the exhaust pipe. If you do decide to replace the O2 sensor DO NOT get a cheap universal type O2 sensor. Get a direct fit. Bosch makes a good one and they run about 50 bucks in my area. There are tests to perform in order to check the O2 sensor but will not put that on here at this point because I believe it's just a vacuum leak. If you have anymore questions or need any other testing procedure you can reply here or feel free to email me directly at [email protected] Hope I was able to help in some way. Here are your pictures.

Check engine lights are designed to turn on because of an fuel/emission problem. You changed the O2 sensor, ****have you reset the computer by disconnected the battery for about 10-15 minutes?**** After you reconnect it drive for several miles to see if it turns on. Run the gas tank empty and when you pump gas try not to pump at gas stations that have E10 mixed with regular gas. BP and shell stations are known for that and can trip the O2 sensor. Try pumping at a gas station like the exxon. If you still have problems with the check engine light, try cleaning the mass air flow sensor ( its located after the air filter and before the throttle body). Also check the gas cap, making sure there aren't any leaks or signs of cracks in it. The best thing to do is to take it a Auto Zone or Advanced Auto and have it diagnosed for free. That could give you a better idea on what to look for if none of these things fix it

a mil light or malfunction indicator light comes on when one of the vehicals emisions sensors is reading somthing that is out of range, possable bad o2 sensor or lean fule burn situation, while the light is on take it to autozone the will checkit

P0131=O2 Sensor Circuit Low Voltage Bank 1 Sensor 1
P0151=O2 Sensor Circuit Low Voltage Bank 2 Sensor 1
Marc,
this shows that the oxygen sensor on the left exhaust pipe before converter is bad,
And the front oxygen sensor on the right exhaust infront of converter is bad.

if the converter was bad the engine would loose power . alot of times the check engine light will come on for the emmitions check youre gas cap some vehicles will send a signal to the computer if the co is not right and by changing the gas cap solved the problem .

There are TONS of reasons - the first , and least expensive, step is to read the codes that the onboard computer is throwing. Instead of spending a lot of money on a code reader, or wasting money by going to the dealership, find an AUTOZONE (or, sometimes MERCHANT's will offer a "we'll check your CHECK ENGINE LIGHT for free) and they'll give you a generic read of the code(s).
I say "generic" because the computer DOES throw specific codes; the "we'll do it free" places usually don't have the same kinds of super-readers that the dealerships or high-end repair shops own. But, bear with me for a sec....this may save you some money.
If the generic code says, "O2 sensor"....that's not as specific as you'd like (because there are multiple 02 sensors!)...BUT....if ONE sensor is not functioning properly, its a pretty good bet that the other(s) will be failing soon too, since they were all installed at the same time and all were made by the same company, etc.
The "generic" code WILL tell you enough info as to which sensor is bad (the one in front of the converter vs the one behind the converter) so....if THAT is the code, then simply replace both behind or both "in front". Follow?
Now, where you'll typically get the most common code is for low fuel pressure. If you've never changed your fuel filter...that's a good place to start. The "generic" code will indicate "fuel pressure". If you've never changed the filter....see? BUT, a fuel pressure problem could also be as simple as "loose gas cap"! If your generic code says "fuel pressure", then I'd reset the computer (disconnect the battery for a few minutes and re-connect), and while the battery is disconnected, make sure that the gas cap is tight and the little rubber gasket around the cap is in tact.
Keep in mind....a "check engine light" doesn't mean that your computer is throwing codes CONSTANTLY! It means that the computer sensed something at some point while the scan was running and SOMETHING got its attention. "IF" the fuel cap was loose, for example, just re-tightening it will not reset the "check engine light"! You gotta reset the computer (disconnecting the battery is easiest), THEN the light will be off. If the light returns, then the problem was something other than the gas cap.
Taking your time and doing a little on-line research can save you a ton of money! A 2000 is relatively easy to work on yourself...at least SOME of the issues...even if you're not a really techie-kinda person. Take the easy and inexpensive shots first....
Hope this helps.

o2 sensors
change to super unlead only