O2 Sensors?

I replaced my o2 sensors in my 2000 explorer 4.0 OHV about a month ago. Its been fine today my check engine light came on im getting code P0171 and P0174 system to lean bank 1 and system to lean bank 2. Are my o2 sensors bad again? I replace all 3. I used bosch sensors are they garbage? Or can it be something else? please help

PO171/174 can be set from a few problems.. Vacuum leaks ect.. But, as a first step, clean the Mass Air Flow (MAF) Sensor with a 'spray only' of throttle body cleaner (not carb cleaner) with the extended  tube tip installed to direct the spray pressure at the wire/s.. The PCM utilizes a heated wire within the sensor and monitors intake air flow over the wire as it 'cools' for a signal for a given throttle angle and volume of air flow.. The PCM uses this signal to calculate fuel requirements.. 'Sometimes' the wire/s get coated with dirt/debris that 'insulates' the wire and throws of the signal to the PCM.. Remove the MAF and look into the bore, you'll see the wire/s on the inlet side.. VERY CAREFULLY spray clean them.. Disconnect the battery to clear the code/s after the cleaning, or clear them with a scanner/reader, and drive it for a few days until the diagnostic monitors complete.. If the CEL doesn't return, then the cause was the MAF...

Thanks ill try it its been real cold here today so maybe that has something to do with it to.

another question to confirm spray the throttle body cleaner in the tube on the maf or where the wires plug in to the maf?

 
You can clean it in 2 ways..
 
Pull the sensor out of the intake/sensor 'body' (but requires a torx bit,) or, you should be able to look into the intake duct from the air cleaner lid.. You'll see the 'nose' of the MAF hanging into the intake stream.. There will be 2 very small 'diode' looking wires stretched across the plastic nose.. These are what you want to clean..
 
Here's a pic of what a dirty one looks like... Not your exact application, but similar..
 


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Whats the mileage on your explorer?

92,ooo miles on it i did it today so well see what happens. I cleared the codes i drove about 150miles tooday so far so good i hope

So were the wires on MAF dirty?

yes that took care of the problem. Thanks alot

Im having the same problem with our explorer 2000 4.0 it has 4 o2 sensors When the code reads bank 1 lean is that the 2 sensors in front of the cat. or is the driver side 2            which ones do i replace?

If its the 2 before the cats. how do you get to the electrical plug on the passenger side.

Bank '1' is always the side of the block that the 'number one' cylinder is on.. Right/Passenger forward cylinder for the 4.0..You generally won't get a P0171 code if the catalyst  monitors (rear sensors) after cat fail.. If it's reading a lean condition, its should be working fine.. A good way to diagnose a bad 02 sensor if no scan equipment is avaiable, is to swap the sensors from bank 1 to the bank 2 position and see if the fault follows the swap.. You would/should then set a P0174 after moving the sensors.. This way helps to prevent replacing good sensors since there are a number of issues or conditions that can set a lean code..

The sensors are numbered as 11 and 12 for the right bank identifying their position, (bank 1 sensor 1 and so on) 11 being forward in the stream, as is 21 and 22 for the left bank..

Hayapower you are awsome! My wifes 01 Explorer with 87000 is bringing up codes PO171 and PO174 I will try to clean the MAF tonight when she gets home from work.
    If I use a can tap and line fuel injectin cleaner, where do YOU hook it up? A friend at a Monroe just uses the brake booster vacume line, I think just cause it's easier. Is that OK? Let me know and thanks.

By the way, I know if I use this method it will do nothing for the MAF. I was planning on doing this independently. Thanks again.

Again, this is only a first step..
 
A common failure for this engine is the upper/lower intake manifold orings failing and bleeding unmetered are (vacuum leak) in.. Along with the codes, it may have an unstable idle when cold that will smooth as the engine heats/expands and the leak seals..
Worth a try, and also look for any other unmetered leak points PCV ect....

No rough idel just codes, the MAF looked clean as could be. ,the battery is still unhooked at this time, and has been for over 15 minutes so I hope code will reset. My wife has shopping to do latter I will see what happens then.
  Also as I had asked where is the best place or proper, to hook up fuel injection cleaner line?  Thanks

Well it's only getting worse. Now it dose have a rough idle. Guess I  will be doing the intake O rings soon. Any tricks or tips to this job? Thanks

I have a 02 Explorer XLT v6, 4.0 69,000 miles, my CEL came on a couple months ago, had this thing into the Ford Dealership, they put it on the computer and came back with P0401 and P1131 codes, and told me I needed to replace all the 02 Sensors, DPFE, IAC, MAF, EGR, and the PCV Valve.  and wanted $1300.00 to do so.
 
I got a code reader, and pulled the codes myself, and got a P0132 (Upstream Oxygen Sensor circuit high voltage (right cylinder bank) is this the O2 closest to the engine on the Drivers side? if so, I  changed that 02 back a couple months ago.  Should it still be throwing this code if that is a new sensor in the bank?
 
I am also pulling a P0401 (Exhaust Gas Recirculation) (EGR) valve, insufficient flow detected.) I would assume that I need to replace the EGR, Correct?
 
Pulling code P1131 as well.
 
If someone can give me some much needed input, I sure would appreciate it.
 
Thanks