Oxygen sensor

So the other day the wife calls and says the "Check Engine" light came on. I whip over to Auto Zone to have them do a error code check. The guy says it's the oxygen sensor 'Bank 2, Position 1'. The part is $50 and and can be changed easily. So I buy it and replace the sensor which is located on the exhaust pipe after the manifold and before the catalytic converter.
It was a pain to get unplugged, but got 'er done. I disconnected the battery to reset the computer and everything seemed to work, and the engine light went out. The next day the light came back on:banghead: . I took it over to Auto Zone again and gave them the 'What-to-for" about the sensor not solving the problem. After checking the codes again, it is both right an left sensors, which he says means the sensor in the fresh air return located after the air filter cowel is bad. THIS part is $138.

So My question is, will this solve my problem, or am I chasing a chicken.
Has anyone else ran into this?!!

Sean

the sensor in the fresh air return located after the air filter cowel is bad. THIS part is $138.

I've never heard of this part, that I know of. There's many other things that can cause an O2 code such as a lean/rich mixture, bad wiring, etc. I think the guy's trying to sell a part, or he has no clue what he's talking about...

You hit the code!! I forgot to mention that was what the code said.

"Lean mixture"

And the guy said because it was both sides it must be the main sensor by the air filter.

Sean

OK, he's a 'tard, he must be referring to either the MAF or the IAT but he'd be wrong on both accounts. I'd start looking at things that would cause too much oxygen to be in the exhaust such as spark plug/s mis-firing, low fuel pressure, etc..

Not that I'm a mechanic, but what is MAF or IAT? Also, what would be some ways I could check for low fuel pressure, or the missfiring and resolve it?!

Thanks for the help!!

Sean

Mass AirFlow Sensor and Intake Air Temp Sensor. To test fuel pressure, you'll need a pressure guage and install it on the test port on the fuel line near the injector rails on the engine. If it's a mis-fire, changing the plugs/wires will possibly fix it. When a plug misfires, unburned fuel and oxygen travel out the exhaust. An O2 sensor can't see unburnt fuel, only oxygen, so it thinks there must not be enough fuel delivered to get complete combustion, so the computer usually adds more fuel, which usually floods the other cylinders that were running fine in the first place. I'd first pull all the old sparkplugs out and replace them. By the way, what year is your car? How many miles?

Mass AirFlow Sensor... that is what the guy said was by the air filter and needing replacement.
I sort of agreed at first because the air filter cover was not clipped in place when I was looking everything over. So it had been sucking air from the outside for who knows how long.

When she first starts it up in the morning, it idles really rough. Then it runs OK,and if she shuts it off, and runs into the store and comes out, it idles OK after that!

It is a 2000, and has about 77,000 miles.

I'm not sure that'd cause it unless there's physical damage to the sensor. Try pulling it out and inspecting it.

What model year is the Mountaineer?

The MAF could contribute to the downstream codes, and it is not all that uncommon for the sensor elements to become contaminated. Especially if using a K&N/oiled filter or, in this case, air that is not passing through a filter.

If you have a steady hand, you can clean the elements. Pick up a can of electrical parts cleaner (you can get this at many auto parts stores), remove the MAF sensor (which may be held in with security Torx screws) and generously spray the two sensor elements.

Based on what you mention about a rough idle when cold, you should also consider an out-of-spec coolant temperature sensor (not sender which controls the guage) or an issue with Exhaust Gas Recirculation (EGR) system (contaminated valve or faulty DPFE sensor -- another common problem).

-Rod

You know they make MAF cleaner now? It seems people using carb cleaner and brake parts cleaner were ruining their sensor. I try to use TV tuner/electrical cleaner or alcohol and a Q-tip..