check engine light

i have a 2000 xls with the 4.0l ohv in it last week i changed the spark plugs and wires canged the oil too then on sunday we get our first snow fall not much 2 maybe 3" i go outside clean off the windshield get in and start driving about a 1/4 mile away my check engine light comes on i go to auto zone and have them pull the codes p0171 and p0174 come up he tells me i need two new o2 sensors i tell him yea ok just clear the codes if the light comes back on i'll come back and buy them i drive about 20 miles home and still no light could it be a false code what would cause the light to come on in the first place what could be the problem what do the codes mean could it be from not cleaning the snow off the grill and hood or maybe all the stuff i did the week before i've changed plugs and wires many time before why did the light stay off once the codes were cleared any help would be great thanks

Those codes do not mean the O2's are bad. It indicates the engine is running lean. Check for a vacuum leak that will affect both banks of the engine.

way2old is eggzackly right. I doubt very seriously it's an o2 sensor. Make sure you didn't disturb or crack the vaccum hose to the pcv valve when working on the engine. Common problem area.

i forgot to mention i changed the pcv valve too geting hit with 5 to 7" tonight post back as soon as the weather clears up

i have a 2000 xls with the 4.0l ohv in it last week i changed the spark plugs and wires canged the oil too then on sunday we get our first snow fall not much 2 maybe 3" i go outside clean off the windshield get in and start driving about a 1/4 mile away my check engine light comes on i go to auto zone and have them pull the codes p0171 and p0174 come up he tells me i need two new o2 sensors i tell him yea ok just clear the codes if the light comes back on i'll come back and buy them i drive about 20 miles home and still no light could it be a false code what would cause the light to come on in the first place what could be the problem what do the codes mean could it be from not cleaning the snow off the grill and hood or maybe all the stuff i did the week before i've changed plugs and wires many time before why did the light stay off once the codes were cleared any help would be great thanks


I have same problem...in researching this problem it can be caused by multiple little problems. For example not seating your oil dipstick correctly. Other problems could be your Mass Air Flow Sensor. Ford Motor Co. has posted a service recommendation.

Good Luck.

well its been 3 days since i had the codes cleared and still no cel but if it does come on again with the same codes i will look into ot and post back nothing wors then someone who doesn't post the fix these were some helpfull answers but can someone tell me why the cel has not come back on thanks for the help guys

The CEL will not come on unless it detects a problem on 2 consecutive drive cycles. If the vehicle does not have the problen re-occur, it may be off for a long time. Eventually it will return and we can go back to it.

ok so it came back on today were should i start to look for the problem

First check for vacuum leaks. If there are none found, carefully remove and clean the MAF sensor. There is a good post on the forums on how to clean it. Just do a search. You will really need a scan tool that is able to read the sensor parameters to determine the exact cause for the codes. Low fuel pressure can cause these codes too. So can a minor exhaust leak.

ok will do we have been geting hit with snow here in new jersey left and right so as soon as i get a chance i will go get a scanner any idea's on a good scanner

Search the forum about a loose fuel filler cap, or a defective one. I recall something as simple as this will set off the CEL because the fuel tank/vapor lines/charcoal cannister are all sealed systems.

A loose fuel filler cap will cause EVAP leak codes, not engine too lean codes. Most likely a vaccum leak or MAF problem like way2old has suggested. If you changed the pcv valve, that would be a fine place to start checking, especially where the plastic tube from the valve connects thru a short rubber hose to the throttle body.

didn't get much snow this time
going to clean the maf today post back with my findings latter

cleaned the maf it was dirty checked for vacuum leaks checked the hose going to the pcv it looked like it was new no cracks wait to see if the cel comes back on let you know

What kind of gas mileage are you getting? If it's the O2 sensor's your gas mileage will really go down. I have a '96 Explorer and my check engine light came on. I had to replace the O2 sensor before the Cat, and the EGR valve. My gas mileage went from 14 city to about 17 city. The CEL hasn't been on since. Just figured I'd throw that out there. Oh yeah, get used to the CEL, it seems to come on a lot in Explorer's.

my mpg have gone a mile or two since i cleaned the maf and it does run better too i have drove about two hundred mile with no cel but who knows with these thing i got a ford service manual off of ebay and this is what it says



NOTE:
It is necessary to address all Continuous Memory Ignition and Misfire DTCs, if received during Continuous Memory testing, before addressing any Fuel Trim DTCs.

Fuel System DTC Reference List:

-- Bank 1 = DTCs P0171 (lean) and P0172 (rich)

-- Bank 2 = DTCs P0174 (lean) and P0175 (rich)

l Check intake air system for leaks, obstructions and damage.

l Check air cleaner element, air cleaner housing for blockage.

l Verify integrity of the PCV system.

l Check for vacuum leaks.

l Are any of the above concerns present?

Yes
REPAIR as necessary. COMPLETE KAM Reset.

No
GO to «DC25».