Code 171 & 174

[Blee1099]

Just recently changed the two front O2 Sensors. Did passenger side and then the driver side about a month later. Just recently the CEL came on and pulled the following codes 171 & 174. O2 Sensors are snug and the connectors are on tight. Wondering if it could be anything else that is causing the CEL.

 

[Msupertek]

Ford Certified Technician

All those codes mean are that your engine is running lean. It does not mean that it is the O2 sensors. Things that can cause a Lean Mixture is as follows:
VACUUM LEAK (very common on older explorers because vacuum modulator lets tranny fluid bypass diaphram and swells up vacuum lines causing leak inspect lines for swelling on top right of intake and repair as necessa)
LOW FUEL PRESSURE (should be 32 psi at idle and spike up to about 38 or higher when snapped throttle)
CONTAMINATED MAF SENSOR (there are tons of threads in here on how to clean it - clean the hot wires if debris is present on them will alter reading to pcm )
CLOGGED INJECTORS ( will be hard to diagnose but usually if one is clogged enough to cause a problem you will have a misfire on one ore more particular cylinders)
RESTRICTED FUEL FILTER (will show up if you perform fuel pressure test and pressure is low)
EXHAUST LEAKS(sense you have two codes for both banks this is probably not is but if your exhaust had leaks near the 02 sensors this could trick them lean)
PCV VALVE (if it is not operating properly or is not the correct application I have seen them cause drivability concerns)

 

[Runnin'OnEmpty]

The code 171 indicates that "the O2 sensor voltage is not switching" (from code scan booklet). That sounds like the sensor either isn't working, or there is an open in the wiring. Make sure the wiring isn't laying on an exhaust manifold and burned open. If everything looks OK, you can test the sensor with a multimeter. Most repair manuals have the procedure.

 

[KodeBlu]

Originally posted by Blee1099
Just recently changed the two front O2 Sensors. Did passenger side and then the driver side about a month later. Just recently the CEL came on and pulled the following codes 171 & 174. O2 Sensors are snug and the connectors are on tight. Wondering if it could be anything else that is causing the CEL.

Just wanted to put my two cents in. I had a CEL on my X. I took it to Goodyear so they could scope it. It came back with the same codes, 171 and 174. The tech told me that Ford has a 50,000 mile emissions warranty and I should take it to them because it should be covered. He also mentioned that I should put the factory air filter back on before taking my X to the dealer so that can not say that the filter (KKM) is causing the CEL. Anyway, I came back home and disconnected the battery cable so I could change the filter. While under the hood, I was doing a little visual inspection and I noticed that a hose was loose. I tightened the hose up, finished changing the air filter and reconnected the battery cable. I started the X up an no CEL. I really don't think that the KKM had anything to do with it because I've had it on for almost two years with no problems or CEL's. I am inclined to believe that when I had my remote starter installed that one of the techs may have bumped the hose loose by mistake. So in saying all of that...I would check to make sure that all of the hoses are tight and secure. Hope this helps.

 

[Msupertek]

FORD CERTIFIED TECHNICIAN

Hate to break the new but I work at a Ford Dealer, I am a Master Certified Technician with Ford and a group leader in the shop. Ford does have an extended emissions warrantly but it DOES NOT COVER 02 SENSORS, NEVER HAS. It covers catalytic converters and the pcm, etc. Your first mistake was taking it to an independent shop. The ford dealer will require you sign the hard copy stated that you will pay a diagnostic charge if it is not covered by emissions warranty which it won't be. Also as far as the code book saying the code means 02 is not switching, I am not looking at a code book from autozone I am using the Factory Ford PCED manual. Sometimes aftermarket books don't have the correct information, since Ford makes the vehicle they usually have the correct meaning.

 

[Robert]

P0171 = System Too Lean (Bank 1)
P0174 = System Too Lean (Bank 2)

As Msupertek said, there are many more things than just bad O2 sensors that can cause a lean condition. My experience is that if an O2 sensor is at fault, I have gotten other codes than the P0171 and P0174. There are codes for the sensors not switching quickly enough or for them being out of range (open or short). If you are getting a lean condition code then all that means is that your O2 sensors are detecting that you have more air in your exhaust than you are supposed to have. It doesn't mean that the O2 sensors aren't reading it properly. Look at the areas that Msupertek suggested. The two most common causes are an intake leak after the MAF (allowing unmeasured air to get into the cylinder) or a dirty MAF which causes it to not read as much air going through it that is actually going through it.

In addition, OBD-II codes are 4 digits, not 3. Since you didn't include the first digit, everyone is assuming that you are referring to codes P0171 & P0174. If by chance you are referring to a P1171 or P1174 then they stand for:

P1171 = Rotor Sensor
P1174 = Cam Sensor