Lean Code’s P0171 and P0174 – Common Causes
June 14, 2009 10:47 am DIY, Ford Problems, How To Auto Repair, Lean Codes
Ford Expedition lean codes could caused by a leaky PCV hose.
If a car has a check engine light on and has P0171 and P0174 codes stored, the most likely cause is a vacuum leak. These codes are set by the car’s computer when it sees too much oxygen in the exhaust. Excessive oxygen readings in the exhaust will set lean codes. This does not mean that the oxygen sensors are defective. It is a common mistake for people to replace oxygen sensors when lean codes are present. Just because the code is related to oxygen sensor readings, it doesn’t mean that the oxygen sensors are bad. If both of these codes are stored this means that both banks of the engine have excessive oxygen in the exhaust. If the oxygen sensors are replaced it’s most likely that the same codes will reappear. It is very uncommon for two oxygen sensors to fail at the same time.
Therefore the most likely cause of P0171 and P0174 codes is a vacuum leak. The source of a vacuum leak can be one of many things. The most common cause of a vacuum leak is a leaky hose. Vacuum hoses over time can become dry and brittle. The rubber deteriorates and can leak causing a vacuum loss. Many times a leaky vacuum hose can be found by listening for a hissing sound. A large vacuum leak can even make the car run rough at idle. In some cases it will not idle without feathering the gas pedal. Another way to check for a vacuum leak is by using a propane bottle with the hose attachment. By introducing propane to the area where the suspected leak is you can sometimes notice a change in the idle. This is particularly true with cars that don’t have computers. Cars that have computers can quickly compensate for the change in fuel mixture. This makes checking for vacuum leaks in this manner more difficult. If you have access to a scan tool, checking the oxygen sensor readings or fuel trim can be done while checking for leaks with propane. If the readings increase when you are adding propane to be suspected leak area, this indicates a vacuum leak. Another way to check for vacuum leaks is with a smoke machine. Evaporative smoke testers can be used to check for vacuum leaks as well. Evaporative leaks have to do with fuel vapors and a smoke machine is used to find those leaks. But evaporative smoke machines can also be used to find engine vacuum leaks easily. To check for engine vacuum leaks with a smoke machine, just find a vacuum hose that goes to the engine and attach the hose on the machine. When the smoke machine is turned on, smoke will enter the engine and help reveal the vacuum leak source. It is common for some smoke to come out out certain areas without indicating a vacuum leak, so if you think you’ve found a leak with the smoke is best to double-check it to make sure. The smoke machine is a great time-saver and can help pinpoint vacuum leaks quickly.
Mass Air Flow (MAF)Another cause of P0171 and P0174 codes can be from a damaged mass airflow sensor. If the reading from the mass airflow is incorrect, the computer can be doing its calculations with wrong numbers. The computer bases the fuel mixture partially based on the amount of incoming air. If the computer sees more air entering the engine than what is actually going in it will enrich the mixture. Therefore if the computer sees less air than what is actually going into the engine it will decrease the amount of fuel in the mixture. Mass airflow sensors can be damaged by dirt getting past the air filter and sometimes from oil that can come off of aftermarket air filters such as K&N. K&N air filters have to be lightly oiled and if excessive oil is applied some of it can come off and end up in the mass airflow sensor. If oil contaminates the sensor it can cause skewed readings.
Fuel Pressure Incorrect fuel pressure from the fuel pump can also rarely cause a lean condition. The fuel pump regulator could be allowing the wrong amount of pressure to be pumped to the fuel injectors. If a fuel filter is clogged or restricted this can alter the amount of fuel that reaches the injectors also. Fuel pressure is not likely to cause lean conditions though, due to the computer’s ability quickly compensate and adjust the air fuel mixture.
Some comments from readers.
We recently had a check engine light come on and after having it scanned at a local parts store we replaced an oxygen sensor. The parts store employee had recommended the oxygen sensor replacement however the code quickly returned. After going back to the parts store they recommended a fuel filter. After buying a fuel filter and going home my husband was about to install it when I searched online and found your article. After explaining to my husband that the cause could be from a leaky vacuum hose, he ran the car with the hood up and we could hear hissing. The problem was exactly what you said, an inexpensive rubber hose. Thanks so much for sharing this auto repair tip. Although the parts store employee was trying to be helpful he was recommending replacing parts that were not bad. I don’t think he was doing this intentionally, but it was starting to cost us an arm and a leg! Thanks again for all your help.
Here’s our experience, my wife’s 2003 Ford Expedition was stalling out while driving slowly and at stop lights, etc… We took it to an Advanced Auto parts store and they scanned it with a code reader and said it was the bad coil and spark plug. We changed them but did not get any better. We thought maybe we had a defective part, so they exchanged them and we installed the parts again to no avail, it was still stalling. We took it in again yesterday the parts store said it was the fuel filter. We took the car to the Ford garage and had that changed, but it was still not running right. They did a diagnostic test and came up with the PO171 and PO174 codes again. I searched those codes on the Internet and found your site and read automotive repair blog. My wife read that there might be a leak in a vacuum hose. She reminded me that she had heard hissing noises over a week prior and had mentioned it then. I didn’t listen, forgot about it until she said again, “I told you I heard hissing sounds a while ago!” So I checked the hoses and found that there is a leak at an elbow in one of the hoses! No telling how long this would have gone on, but with your help we were able to repair the problem ourselves and not continue throwing money at the problem. Thanks for your help and I will recommend your site to everyone I know!
Mike :
Date: August 9, 2009 @ 5:43 pm
I have a 2001 Jaguar S-Type. It was throwing a code P0171 as well as P0174. We took it to the mechanic and they said it could be a number of problems, so I researched online and found your site. It was the Intake hose on the TOP of the Motor. I could Hear “Hissing” and it was very easy to replace. The new hose only Cost me $6
Thank you very much for your help! You saved me alot of money~
sprawlking :
Date: April 22, 2010 @ 10:22 pm
I’m writing to hopefully provide solace for those who are perplexed by these two bewildering codes. I recently had an issue with these two codes occurring together. From the outset, I paid for a diagnosis at the service dept of my local Ford dealership. They failed to make a diagnosis. I made it clear to them that I had no intention of throwing thousands of dollars at every symptom they could come up with (…and belive me there are many variables); but apparently this had been their plan. It’s inconceivable that the mechanics would have had no experience in dealing with other distressed Explorer owners–enough to know how to resolve the issue without expensive “guesses”. Once I paid for a diagnosis I was determined to hold their feet to the fire–showing up at the service dept everytime the light came back on. Eventually, I gave up and begin the arduous process of elimination. I had spent approximately $300-350 replacing the (mas airflow sensor, Throttle position sensor, and the oxygen sensor). After replacing all these, the light immediately came back on. Forutnately, I took it to a trustworthy mechanic who did a thorough investigation (before my very eyes), before rendering an opinion. He said that the problem was most likely the (intake-manifold gasket). I paid him 225.00 for the diagnosis and to replace the gasket and I’ve been worry-free ever since. The point I am trying to make is for anyone distressed by this should first consider this before spending hundreds of dollars needlessly in replacing all the sensors. Undoubtedly, it’s a money making scheme–dreamed up by the engineers at Ford.
dennisb - Auto Tool Sales :
Date: April 23, 2010 @ 6:26 am
Sprawlking, thanks for the comment, I appreciate you taking the time to vent… I mean share your experience :). Intake gaskets (actually upper plenum gaskets) on most Ford Explorers are similar to rubber o-rings. They are a common problem that many times can cause vacuum leaks on 4.0’s. Sometimes they only leak when cold, making them particularly hard to detect by the time the vehicle has been driven to the shop and reach normal operating temperature. This would possibly explain why an Explorer with this problem may run rough or at an excessivley high idle until it warms up.
Hoon :
Date: September 13, 2010 @ 9:25 am
i have an issue. had a vacume leak for some time, and now my truck has random delays in starting.
dennisb - Auto Tool Sales :
Date: September 13, 2010 @ 10:16 am
Could be related if the problem occurred immediately after the vacuum leak was repaired. It sometimes takes a little while for the computer to put it’s fuel/mixture strategy back into place after it the air intake is back to normal. It’s also possible that the problem you are now having may not be related at all. I would try cleaning the throttle plates and if the problem persists and there are NO codes stored – check for fuel pressure bleed down. Some pressure should remain in the fuel rail, 0PSI in the rail when a start is attempted, will cause a delay in the engine starting.
Larryh :
Date: December 12, 2010 @ 10:51 pm
My 2000 ford F150 is showing only the PO171 code by it’s self. Could it still be a vacuum leak or would you suspect an 02 sensor?
dennisb - Auto Tool Sales :
Date: December 13, 2010 @ 8:14 pm
Larry, I would look for a vacuum leak. However, lean on both sides would be more of an indication of a LARGE vacuum leak. Good Luck
joe :
Date: April 4, 2011 @ 5:15 pm
03 jag x type. p0171 & p0174 codes set. won’t idle cold. misses.
dennisb - Auto Tool Sales :
Date: April 4, 2011 @ 6:05 pm
Joe, sounds like a vacuum leak. that’s the first thing I would check. Good Luck
Mike G :
Date: April 12, 2011 @ 12:10 pm
I have an 05 saturn vue 2.2 l. And it runs rough some times and. It brings up 171 and 172 codes. Not sure where to start thanks
Jeff :
Date: April 23, 2011 @ 5:31 pm
I have a 1998 ford f150 5.4 liter with the codes p1131,p1151,p0171,p0174,p0156 as well as a p0113 code. It barely idles and often dies when I come to a stop unless I push on the gas pedal while pushing the brake. When I spray starting fluid towards the back of the motor, It revs up. So this tells me it’s a vacuum leak, But since the fumes spread out, I’m not sure how to pinpoint the exact leak. Any ideas?
dennisb - Auto Tool Sales :
Date: April 24, 2011 @ 8:32 am
Jeff, You could use a propane bottle and a small rubber hose to more precisely check certain smaller areas. However, a common leak on your motor is the PCV hose. It could be a collapsed elbow, could be leaking or both.
Sometimes you can even hear vacuum leaks on these trucks. Look for collapsed hoses coming from passenger side rear of manifold going to PCV valve. This is by far the most likely cause of the leak. Another possibility, although less common would be intake gaskets. Look for simpler, easier fixes first. Good Luck.
Jeff :
Date: April 26, 2011 @ 11:33 am
I just found the vacuum leak. The small rubber elbow at the end of the pcv valve that connects into the intake under the idle air control valve had a huge hole in it. It’s hard to believe that a $10.00 dollar rubber elbow caused so many codes to be thrown. But for now, It seems to be running better than ever. Thanks for the help.
ron schroeder :
Date: June 29, 2011 @ 12:41 am
Hi dennisb I have a friends 98 mercury mystique 2.5L v6 with p0171 p0133 p1151 & p1131 trouble codes my buddys snap on scanner said p1131 mass air flow sensor out of range, do u think this could be causing all the codes for bank 1 & 2 & if so should I try cleaning it or replacing it. also gonna check for vac leaks, also thinking about cleaning iac valve, egr & throttle body, etc. just wanted your input. this is a friends car & im trying to help him pass emmissions without breaking the bank, which with high miles I know may be hard. thanks ron.
dennisb - Auto Tool Sales :
Date: June 29, 2011 @ 6:49 am
Ron, since you are in the repair business (selling tires) you may be aware of what most mechanics call the Mystique – a “MISTAKE”. These cars had a horrible problem with the fuel injector harness insulation. Be sure not to move any of that wiring if it can be avoided. I had an experience with one of these when inspecting for resale at a car sales supercenter a decade ago. There were so many problems with the car, I wanted it to be auctioned off for wholesale instead of repaired and sold for retail on the front lot. The buyers, for whatever reason, did not listen. When the engine compartment was pressure washed during the detail process, the crumbling, brittle plastic coating (or insulation) was blasted away from the wiring. The car would no longer run and had to be pushed out of the detailing area. A new FI harness at that time was only available in a complete wiring harness for the engine and was going to cost around $1500. Instead, we ended up removing the intake manifold and using black electrical tape on the entire FI harness. The car was then placed in a wholesale auction like I had originally recommended!
OK, now that I’ve vented – back to your issue at hand… I would check for vacuum leaks first and foremost. Cleaning the IAC would certainly be a good idea, but probably wouldn’t have any effect on the codes set. A dirty MAF (MASS AIR FLOW) sensor could set a lean code possibly, so you could carefully clean that. Also check motor mounts to insure that too much engine travel isn’t pulling on the air intake hose from the MAF to Throttle. A leak past the MAF will allow unmetered air which could result in a lean code. And it would be out of range due to the leak as well. If still setting codes after fixing the above possible issues, there could be Oxygen sensor problems – see our P1131 related article for more ideas to help with diagnosing. Good Luck.
ron schroeder :
Date: June 29, 2011 @ 3:49 pm
ok well I cleaned maf & trottle body, gonna change oil too & plugs n wires since wire appear to be arching but I know thats not causing these problems. I read that I can try unpluging maf & drive car to see if codes come back or not. I also seen one hose on large rubber boot kinda loose so I pushed back in. I also did hear hissing in driver back of engine & it appears to be sometype of hose going from lower intake I believe going to egr soneiod I think? (passenger side of engine) but it has a sprial tubing type thing over it & it appears to have fuel line like fittings on both ends. unless it is a fuel line & im just hearing fuel running through it. I tried spraying with carb cleaner but didn’t seem to change much even after unplugging maf. I also hear possible coolant temp sensor or possible crank or cam sensor (cam timing) I even hear worn engine? too car has about 125K well thanks for your input on this POS LOL
ron schroeder :
Date: June 29, 2011 @ 3:55 pm
o yea one more thing, even tho changing both upstream o2 sensors with the miles, good maintence. I hear it is highly unlikey that both would go bad & cause these codes to pop up, I cleared codes after cleaning maf & throttle body. Plus I even cleaned upper intake with seafoam by running it through vac line that feeds all cylinders, to see if its sticking injectors or such & put lucas fuel treatment in gas tank & might even try running some shell v power through. well thanks for your time & have a great day, gotta check out some of your tools too sometime lol if wife will let me spend the money. =)’
Doug L :
Date: July 16, 2011 @ 9:25 am
I have a 2002 Saturn Vue with a V-6 and AWD. The car randomly does not start and then miraculously does. Sometimes right away, other times after a few hours. I did have a code P0174 but am not so sure this could cause my problem totally. Any thoughts or ideas?
dennisb - Auto Tool Sales :
Date: July 16, 2011 @ 2:55 pm
When it’s not starting I would do a fuel pressure test. Could be a fuel pump failing. Good Luck.
george :
Date: August 18, 2011 @ 9:33 pm
My 2002 f150 4.2 later keeps having a hissing noise after I changed the isolator bolts and intake plenum gaskets as the Ford tsb bulletin described.I have checked for vacuum leaks on all hoses with carb cleaner and no change.I still keep hearing the hissing coming from the middle of the engine or where the intake plenum is. at this point I have no idea what to do anymore. The check engine light has not come back on after 200 miles but it still wants to stall at idle and going over bumps in the road in 1st and 2nd gear.any ideas what it is?
Gary Greesimunkee :
Date: August 29, 2011 @ 4:46 pm
Those 2 codes showed up and I heard the hissing. I couldn’t tell you where in the heck the oil goes… but I own that leaky vacuum hose problem. FIrst thing that’s ever been fixed on my car- where nobody went “prison style” on me after being fixed.
dennisb - Auto Tool Sales :
Date: August 29, 2011 @ 6:01 pm
Gary, you may even gain a side benefit of “less oil consumption” after fixing the vacuum leak. Without the huge vacuum leak, the PCV system will work properly and the engine may burn less oil now.
Yu Fu :
Date: September 27, 2011 @ 11:22 am
Hi. My 2003 Ford Taurus had Service Engine Soon lamp on and showed the code P1131 lack of heated oxygen sensor, bank 1 sensor 1, 1)switch indicates lean. P1151 heated oxygen sensor, bank 2 sensor 1, switch point indicates lean. P0171 bank 1 system too lean. P0174 bank 2 system too lean. Any ideas what shall I do with it ? Thanks.
owen scott :
Date: October 13, 2011 @ 12:35 am
got the codes on my 06 fusion v-6. MAF is good. no vacuum leaks fuel pressure at 35psi. ford says 48 to 70 psi. code is intermittent. usually at low idle or low rpm. any help.
dennisb - Auto Tool Sales :
Date: October 13, 2011 @ 6:42 am
Owen, although rare, low fuel pressure can cause a lean code. Your reading is below specification, so there is a problem there that should be addressed regardless if it is causing the lean codes.
Vacuum leaks are sometimes hard to find because they are small enough to NOT seem to affect the quality of idle or performance. Also, vacuum leaks may only occur when the engine is cold and first started up. After the engine warms, due to expansion, the seals may fit tighter and there’s no leak. That’s why it may be worth smoke checking the engine when it’s cold. A common leak on your engine would be the intake gaskets.
It’s always a good idea to check for TSB’s (Technical Service Bulletins). Sometimes computer reprogramming or “flashing” is done to tweak parameters slightly. This is done when the manufacturer recognizes there’s really no mechanical or sensor failure, but codes are set due to certain conditions that they did not account for. That’s why it’s always best to check for a related TSB when there seems to be nothing wrong when checking the basics. Good Luck.
kita :
Date: October 18, 2011 @ 5:28 pm
I have a 96 bonneville and we put it on a scanner and it stated po171 and something about random misfire..and of course when I went to emissions I failed trying to get it registered. Now my question to you should I waste my time and money with this car because I only paid 500 for it and put about 600 into it already…I’m just trying to way the odds.thanx
dennisb - Auto Tool Sales :
Date: October 18, 2011 @ 5:37 pm
Kita, those codes could cost a few dollars to fix or it could be several thousand dollars. if I were you, I would get an estimate for repair and make sure they know the purpose is to pass emissions. After you know what the cost is you can decide. Good Luck.
kita :
Date: October 18, 2011 @ 6:08 pm
Well I took it to the repair shop and he fixed the gas leak and he said the fuel pressure was under 20 and it suppose to be higher..then he said I might need a fuel pump but when me and another mechanic checked everything out he said its a vaccum leak..so im confused as far as what to do or who to believe.
dennisb - Auto Tool Sales :
Date: October 18, 2011 @ 6:15 pm
Kita, I would find a reputable shop and stick with them. They should be able to make the repairs and check the emissions readings in the shop so that you know you’ll pass before going back for inspection. If they don’t have the equipment or the confidence – then find a shop that does. Good Luck.
Kered :
Date: October 24, 2011 @ 8:35 pm
Ford Expedition with po171 code.
Replaced O2 sensor bank 2
Replaced MAF
Replaced PCV
Replaced PCV elbow ( found leak)
Replaced spark plugs
Car runs rough under 40 mph on hwy.
Runs great with 1/2 tank full on hwy but still feeling stuttering and misfire. I apply gas pedal which corrects problem temporarily.
Any Suggestions ????
dennisb - Auto Tool Sales :
Date: October 25, 2011 @ 6:48 am
Kered, since you say it runs great with 1/2 tank full, you may have a venting issue (not sure if I’m misinterpreting what you are trying to say) . Otherwise if I were checking it I would smoke test for more vacuum leaks and check Mode 6 for misfires that may not have set a misfire code yet. Good Luck.
Miranda :
Date: November 21, 2011 @ 6:14 pm
I feel like a fool, so listen up people!! I have an 04 Mazda Tribute…sure enough I was also driving around town when my engine light came on…hmm 2 days later my car started rough idling at a stop in park or in drive. I looked up the P0171 and p0174, and read the research about vaccum leaks too. I checked for vacuum leaks and found none, moved on to cleaning the MAF sensor and carb, air filter, spark plugs and wires (which were fine..just in my frustration i thought it couldnt hurt), I was SOO close to, dropping $100 bucks for a new oxygen sensor…if that didnt work, I was going to give up and put it in a shop…but sure enough it WAS a vacuum leak!, right on top toward the back there was an ‘elbow’ hose pinched together why i never heard or saw this I just don’t know!!! but check people check with your eyes and ears before spending money like me! BTW codes are clear she’s running beautifully! Good luck all! p.s mine sounded like somebody letting the air out of a tire real high pitched, maybe I couldnt hear it until it got worse i just dont know
oscar ortez :
Date: November 26, 2011 @ 8:53 pm
I had a code p0171 and p0174 on my 2001 ford expedition. and same thing It was a vacuum leak on the back of the intake. Thanks to you guys. If everybody would share a litle bit of our knowledge we will have a better world…
Mike :
Date: January 30, 2012 @ 11:14 am
2003 5.7 Silverado. For months now, 171 and 174. I have replaced plugs, wires, MAF, fuel filter, evac canister (by shop). They indicated there was no leak. Still runs rough and stalls when cold. Codes will not go away. Any other ideas before I replace the CAT Converter?
dennisb - Auto Tool Sales :
Date: January 30, 2012 @ 11:27 am
Mike, some vacuum leaks are hard to find. Some only leak when the engine is cold which would make since because your’s runs rough when cold. When the engine heats up the expansion could make the vacuum leak very hard to find. I recommend taking to a shop that has a smoke machine and allow them to keep the vehicle overnight and smoke test it when it’s cold the next morning. Could be intake gaskets, that’s what I would pay special attention to. BTW, lean codes NEVER mean a bad catalytic converter. Good Luck.
RaynsMommy :
Date: February 26, 2012 @ 1:29 am
Hi Dennisb,
First I have to say thanks to all the comments on here I feel more prepared to tackle my issue, or should I say the repair shop. So, I would REALLY appreciate your advice because after doing some research, it may very well be that I have a faulty elbow, leaky hose, or dirty filter. I would like to try the inexpensive repairs FIRST, instead of the other way around, especially since the shop suggested the items listed below. Okay, here it goes, I have a 2000 Jaguar S-Type V6 and just a little over a week my check engine light came on. Since then, I noticed my car starting to idle “oddly” while in “Park” or foot on the brake at a stop. It runs fine at all speeds, but, recently over the week it stalled 3 separate times while I in “park” only. It turns right back on with no problem, but of course I want to fix the problem. I have been doing research and I just found this awesome blog and learned that maybe it is a simple repair (crossing fingers and toes) since my car has been “hissing” when the car is cold and in cold weather only. Well, I took it in to the shop earlier today and they said that P0171, P0174, and P0300 registered ( I previously learned what these were when I researched my cars symptoms) and they said that they were trying to isolate which one of the engine sensors was the cause/problem. After a while they came back and asked me if my car had stalled, when, and how often. I told them that only a few times and only while in “park.” 30 minutes later they “recommended” the following under each category. Please note that I didn’t tell them about the “hissing” because I just learned about the potential of it being a “Large Vacuum Leak” So, I would like your advice as to how I should proceed before I give up an arm, a leg and a half!
GASKETS-ENGINE
Intake Manifold Gaskets(Both Upper & Lower) *Parts and Labor $591.04
ENGINE SENSORS
Remove and Replace PCV Valve
*Parts and Labor $278.29
TOTAL with Taxes $893.42
Needles to say I almost passed out, I say almost because I know its a Jag that typically comes with higher repair costs. Oh yeah, and they told me that I should not drive my car too much because it is misfiring…
I THANK YOU in advance!
dennisb - Auto Tool Sales :
Date: February 26, 2012 @ 9:15 am
RaynsMommy, If I were checking the car I would try to pinpoint the vacuum leak. I remember working on a few Jaguar S Types that had a common issue with the PCV vacuum line assembly leaking vacuum. See the image for the approximate location to look. Running more roughly with the brake on at idle goes along consistently with a vacuum leak since the power brake booster draws more vacuum from the engine to provide assisted/power brake action. When the car is at higher RPM’s this is much less noticeable. *Note; A bad/leaking power brake booster could cause the issue too, but is a much less common failure.
The PCV (Positive Crankcase Ventilation) valve is not really a sensor like in the estimate you were provided. If the valve is available by itself and not just as an “assembly” with the hose or molded line altogether, they are rather inexpensive. However, I suspect that the PCV for your car is only sold as the more expensive assembly (probably a dealer only part). While it is possible; the PCV valve “itself” is probably not the problem, most likely it’s the line cracked and leaking somewhere. On some Jaguars, the intake must be removed to access and replace the PCV line assem. That is most likely why the repair shop has given you an estimate for the intake seals as well. If intake seals are re-used there’s a chance they would leak ruining the job. So the only professional way to price the job out is to replace, and not take a chance of the intake seals.
Things you can do.
1. Check for an obvious vacuum leak in the area I pointed out in the picture. If you find a vacuum line try repairing just the section that is leaking. If a plastic line leaks, cut it and use a rubber hose that snugly makes the union. If a rubber vacuum hose leaks, use a plastic line in the same manner.
2. If you end up paying the shop to do the repair, make sure you are not paying for duplicate labor. If you are paying for the intake R&R to access the PCV line assembly, you should not have to pay full price (or full boat) for the PCV line labor as well. This is known as double dipping! It’s OK to pay some labor for the PCV line, you just shouldn’t have to pay double. Good Luck.
Sammy :
Date: March 20, 2012 @ 10:49 am
I have a 2000 ford focus. zts model. It has a ztec engine. single overhead cam. I have a check engine light on. The code came back as a po171 code. A mechanic sprayed brake cleaner all over the ngine and nothing happened as far as leaks go. He stated if it was a vaccum leak it would make hissing and spraying. My next step is the o2 sensor. Do you think this is the problem? I dont want to spend all kinds of unnesscasary money! Please advise…
Thanks,
Sammy
dennisb - Auto Tool Sales :
Date: March 20, 2012 @ 11:02 am
Sammy, a lean code is not likely a bad O2 sensor. Like mentioned in the article, an idle change may not be noticed when checking with a spray or propane.
“Cars that have computers can quickly compensate for the change in fuel mixture. This makes checking for vacuum leaks in this manner more difficult. If you have access to a scan tool, checking the oxygen sensor readings or fuel trim can be done while checking for leaks with propane. If the readings increase when you are adding propane to be suspected leak area, this indicates a vacuum leak.”
Good Luck
Jerry :
Date: March 24, 2012 @ 12:34 pm
No one has mentioned using a vacuum gauge. Can you have a vacuum leak and the gauge reads normal?
Thanks
dennisb - Auto Tool Sales :
Date: March 24, 2012 @ 12:58 pm
Jerry, a vacuum reading that is lower than 17-21″ HG may indicate vacuum leak, however that in itself doesn’t help to locate the leak. If you have both lean codes we already know that there’s a vacuum leak.
Jerry :
Date: March 24, 2012 @ 1:10 pm
I was just wondering if that would confirm there is one, or could there be a small leak enough to set lean both banks and still read normal. I like your info very comprehensive and informative. I got pulled over for an outdated inspection sticker and I’m scrambling to fix this to get it inspected. I don’t want to just take it somewhere were they keep throwing parts at it at my expense, I can do that. I’ve cleaned the maf sensor and changed the fuel filter. going to check the fuel pressure next.
hopefully its not the pump.
Thanks for your help
dennisb - Auto Tool Sales :
Date: March 24, 2012 @ 3:45 pm
Jerry, in my experience low fuel pressure usually is not the cause of these codes. I would look for a vacuum leak when both codes are present. Good Luck.
Jerry :
Date: March 24, 2012 @ 5:21 pm
Thanks Dennis, maybe I’ll have the guy do the smoke test again. The first time he didn’t block the intake up front. I’ll let you know what it ends up being if we find it.
Matt :
Date: April 4, 2012 @ 10:11 am
I have 2000 ford explorer limited 5.0 that also shows lean codes p0171 and p0174. I changed the fuel filter, plugs and wires, o2 sensors, egr valve, maf sensor and a whole new exhaust. Still runs rough at idle and hesitates while driving. I finally gave up and brought it to a mechanic who did the smoke test and could not find a vaccum leak. He believes its the fuel pump. He did a pressure test and said it was low(30 psi) and is recommending i replace the pump. Im gonna have him do it but if for some reason thats not it what else could it possibly be?? Any help would be greatly appreciated.
dennisb - Auto Tool Sales :
Date: April 4, 2012 @ 11:51 am
Matt, although it’s possible, a bad fuel pump rarely causes the lean codes. I would check the air intake hose, PCV line including the 90 degree elbows. The rubber elbows, sometimes will collapse. A smoke test is usually a good way to test for vacuum leaks, but sometimes leaks only show up when the motor is cold. For that reason you may want it re-checked after the vehicle has sat in the shop overnight. Good Luck.
Jerry :
Date: April 15, 2012 @ 2:36 pm
Dennis, do you know what the fuel pressure is supposed to be on a 2000 explorer sport 4.0 I’ve been looking on the net and getting different results. I tested mine on the rail and get 39. also should it vary at different rpm’s
Thanks, Jerry
dennisb - Auto Tool Sales :
Date: April 15, 2012 @ 4:16 pm
Jerry, could be a couple of different types of FI systems. I would look in ALL-DATA for the specific year and engine. Short on-line subscriptions are available for just one vehicle (great for do it your-selfers).
You can access fuel pressure specs along with other repair information. Just click on the Auto Repair Manuals link at the top of this page to find out more about this. Good Luck.
Pat :
Date: May 17, 2012 @ 2:08 am
2003 Taurus ses just suddenly stalled in morning just cranks. Got it running but barely took it to shop they found hole in hose. reset computer off I went $200. Now its stalling again and won’t stay running after it warms up. and cranks then finally starts and have to keep gas on. It stalls at every light and frm going in reverse stopping stalls it. Shop says no more vacuum leaks thoroughly checked. MAF sensor new, IAC checked, connections checked, New o2s, new fuel filter,Cleared codes again still having same issue. Very stumpped. Is it a ford ghost issue?
dennisb - Auto Tool Sales :
Date: May 17, 2012 @ 7:16 am
Pat, I’m curious to what the shop says might be the problem since they are physically there and can check the car with a scan tool, manual test equipment etc.
I would check for pending codes, fuel pressure and also make sure the fuel itself is not contaminated. Depending upon where the vacuum leak was in the hose, the MAF could have trash in it… is the air filter bad and allowing unfiltered air to get into the MAF? All these are things to check, but the technician should have some ideas of his own (if he doesn’t find one that does). Good Luck.