Codes p0171 and p0174

[Triathlete]

Check engine light has been on for a few months now. Finally getting around to fixing since I have to get an emisions test soon. Codes read P0171 and P0174. VX has 110000 miles on it. It still runs smooth. Sometimes gets a fuel smell...like a carburated engine running rich. Codes refer to O2 Sensor for the engine bank two. Does this sound right?
Where is this sensor located?
Local auto zone has the Bosch replacements for $66. Is this about right for the price?
Thanks in advance!

[johnnyapollo]

Sounds like the 02 sensors that are before and after the cats? I bought a couple of OEM units on eBay for around $15 plus shipping - look there.

-- John

[custom]

If I remember correctly that means that Bank 1 and Bank 2 of the engine are running lean. I had that come up a bunch of times on our Ford Windstars at work. Normally I try a fuel cleaner first, then filter next. If those don't work you might have a bigger problem.

[rowhard]

P0171
Fuel Trim System Lean Bank 1
P0174
Fuel Trim System Lean Bank 2

[Triathlete]

Does anyone know where the Oxygen sensor(s) are located and ease of changing? Any special tools?
The computer read out says could be a MAF however I have no power/idle problems. The other thing it says is the Oxygen sensor could be defective.
Other causes it lists would have other sythems such as rough idle or loss of power which I don't have.
Ebay is out just because I procrastinate and need to get it done quick!
I will pick up some fuel system cleaner also just to be safe...and it probably needs it since its been a while.

[Y33TREKker]

Bank One is the passenger side, Bank Two is the drivers side. (Bank One, Sensor One = before cat, Bank One, Sensor two = after cat. Bank Two, Sensor 3 = before cat, Bank Two, Sensor 4 = after cat). It looks like those two codes are telling you that both sides/banks are seeing lean conditions, so it's doubtful that O2 sensors on both banks would go bad at the same time, but stranger things have happened I guess.

They basically thread into bosses on the exhaust pipes, so removal and installation are relatively simple using an open-end wrench. The only specific requirement during installation is the use of O2 specific anti-seize for ease of future removal.

While it doesn't necessarily narrow things down much, other possible causes could be vacuum related issues with the intake manifold , the pcv valve, and/or the egr valve.

[Triathlete]

With both codes could it also mean the MAF is dirty or defective?

[Y33TREKker]

With both codes could it also mean the MAF is dirty or defective?

Yes. One of the P0171/P0174 diagnostic steps in the downloadable manual suggests checking the MAF sensor inlet screen for damage, or the presence of foreign objects which may partially block the airflow sample through the MAF sensor.

There's also another MAF diagnostic step that involves disconnecting the MAF sensor electrical connector so the vehicle can be monitored in "closed loop" mode, but it also requires a "Tech 2" analyzer (Isuzu tool?).

[Triathlete]

Thanks Y33. I think I'll do the MAF clean first...its the cheapest! I'll let you all know how it goes.

[Y33TREKker]

How long since the air filters' been changed? That could affect MAF air flow too. You never know, sometimes it's the simple stuff.

[Triathlete]

That was the first thing I tried 3 weeks ago...new K&N. Reset computer and it light came back on 10 minutes after start up.

I bought a $6 can of MAF cleaner, cleaned MAF, dropped a bottle of Lucas injector cleaner in the tank (just because it probably needed it anyways), reset the computer and went for a 20 mile test drive. So far no light. Will get my emission test done tomorrow.
After the holidayys i think I wil replace all 4 O2 sensors...suposed to be done every 100000 miles or so anyways...I'm at 110000!
Thanks again for all the help and suggestions everyone.

P.S. per the can of cleaner...your MAF should be cleaned every time you change (or would change for us K&N or Green filter guys) your air filter.

[Reg Hinnant]

O2 sensors not too hard to change. Getting to the wiring disconnects are the hardest part. I changed out all 4 of mine in a Montrose Colorado Auto Zone parking lot. At that point I knew vacation was over!:rolleyes:

[Kenny]

I replaced my O2 sensor with a Bosch over a year ago and all is still well.
It's a very easy replacement job, though the electrical disconnect can be tricky to get at. I think it was snapped onto the frame with a tab...

I would also take a look to make sure ALL your sensor plug-ins are secure on your intake (I think there are only two on the black plastic body). One came loose on me last year and gave me all sorts of fuel codes.

[Triathlete]

Cleaning the MAF seems to have fixed it. Day 2 and still no light! Pased emissions test with flying colors!
I will put the O2 sensors on my list of things to do though since they are probably about due.
I crawled under the VX last night and they look pretty easy to get to.

[Y33TREKker]

Nice. I only all VX problems were that easy to fix.

[Diogenes]

Hey folks!! Just failed emissions.. "sigh" because there's apparently no input from the O2 sensors.

My rig is a 1999 with only 60K miles on it (yes.. that's correct.. ;), so I'm thinking it might be a MAF related issue and I'd like to explore this before paying the $$$ to take it to a mechanic..

So what kind of MAF related cleaner should I be looking for and how do I use it? Do I just remove the air filter and spray it into the air intake tunnel? I take it I should not do this with the motor running.. ;0)

Btw, haven't had the codes read yet, so this is just a first step.. trying to avoid a major (costly) repair bill if I can.

Thanks for any input you can provide!!

[Diogenes]

Just had my vehicle down at the shop to have the codes read and they informed me that to replace my 02 sensors (all 4 rather than just 1), they'd like to charge me $850..

I declined, but asked for a written estimate since in our state, if the cost of repairs is over $750 to bring the vehicle into emissions compliance, you apparently can get a waiver.

I'll try and deal with the 02 sensors on my own time and see if I can fix/replace them myself.

Diogenes

[johnnyapollo]

They sell for about $50 each on eBay (and sometimes you can get them a lot cheaper - think I paid $14 for the last one I found on there). I'm not sure why they're charging you so much in labor - I think the sensors retail for something like $79 each. It could be an exhaust/emissions issue that is unrelated to the sensors.

-- John

[Triathlete]

To clean the MAF you just loosen the two clamps (one on each side of the MAF) and remove it. You then spray the inner parts of the MAF, according to the dirrections on the can, with MAF cleaner (any auto parts store should carry it...it is a cleaner made specifically for MAFs). I used "CSC Mass Air Flow Sensor Cleaner" that I bought from Checker Auto. It is fairly inexspensive.
As far as the o2 sensors...they are pretty easy to access. They are on the exhaust pipe. If you crawl under the VX you will see them pretty easily. Just pre-soak them with a penitrating oil 3-4 times prior to help loosen then up. Just need the right size wrench and a little elbow grease and you'll be good. Probably less than a 2 hour job if you take your time. As stated already, the sensors are under $80 each. I know checkers has the Bosch sensors for about $75 regular price.
If your state is like Az then you can only get 1 waiver so this is not a long term solution.

[volume311]

I got a pair of new Bosch O2 Sensors for about $55 down here with the harness.

You will need either an O2 sensor wrench or a open ended 22mm wrench. Spray them with some PB Blaster first and they pop right out. Do it in the morning when the pipes are still cold, they heat up pretty quickly. The hardest part on the front ones is getting to the connectors.

[Vehi-Cross-Az]

good thread, and info
just wanted to add my 2¢ for those who want to clean
their MAF sensors.
When I do mine, I take mine off completely
I use white vineger (a mild acid) to clean mine.
Its cheap, works great and plenty of it around.
You can even soak the wire in the vinegar in a bowl
if you want for a few hours..
And when done just rinse it off with warm water.
Let air dry and install.

Triathlete, you should try to swing by my shop
someday. Its on 1st ave just north of Grant rd.

[WormGod]

Just cleared out my 171 and 174 codes this weekend. An intake tear down and a solid blast of MAF cleaner did the trick. Did not bother with the o2 sensors. I just passed emissions about 3 weeks ago (CEL didnt spawn until 2 days after I passed, heh), so I am in no immediate hurry. I will just wait and see if the sensors themselves decide to throw a CEL (I believe that is a 420 if I am not mistaken).

Thought this may be related at first since both popped up about the same time, but it does not appear so. Even after cleaning the MAF and clearing the codes, my VX is still running.... funky. On cold startup, it idles at roughly 2k-2300k. On warm startup, sometimes it simply stalls at idle unless given some juice. This is all new as the S/C has been in for almost 2 years now. I am leaning towards the FPR and/or the EGR. Both were fully prepped and cleaned when I installed my S/C, but considering I have 7 hard years on both, it wouldn't hurt to replace. It may also be one of the reasons why the VX has started to run a bit lean and is suffering minor fuel dump. Thoughts?

[Ldub]

Just cleared out my 171 and 174 codes this weekend. An intake tear down and a solid blast of MAF cleaner did the trick. Did not bother with the o2 sensors. I just passed emissions about 3 weeks ago (CEL didnt spawn until 2 days after I passed, heh), so I am in no immediate hurry. I will just wait and see if the sensors themselves decide to throw a CEL (I believe that is a 420 if I am not mistaken).

Thought this may be related at first since both popped up about the same time, but it does not appear so. Even after cleaning the MAF and clearing the codes, my VX is still running.... funky. On cold startup, it idles at roughly 2k-2300k. On warm startup, sometimes it simply stalls at idle unless given some juice. This is all new as the S/C has been in for almost 2 years now. I am leaning towards the FPR and/or the EGR. Both were fully prepped and cleaned when I installed my S/C, but considering I have 7 hard years on both, it wouldn't hurt to replace. It may also be one of the reasons why the VX has started to run a bit lean and is suffering minor fuel dump. Thoughts?

FPR could be a contributing factor, especially if you didn't pop in a new one when you installed the S-C. BTW, you can get a right angle snap ring pliers that JUST has enough clearance, at Harbor Freight for cheap...:smilewink
The one I got has straight, 45 deg. & 90 deg. interchangable jaws.
Also, the snap ring that comes with a new FPR is too small for the aluminium block on the S-C kit, so re-use the old one.
The lean condition that the codes are indicating, from my past experience, points towards a vacuum leak, either intake gaskets or vac. line.
I've had vac. lines pop off under boost, also check the PCV valve & hose, I recently had the same exact symptoms & it turned out that I had a bad PCV valve. (the top & bottom had come apart):luck:

[WormGod]

I replaced the PCV a few months ago, as well as my temp sensor, so I think those should be good to go. All vacuum lines were pretty solid though I was skeptical of my plumbing for my CAI. I removed all of it up to throttle body and replaced it with the OEM air box, for now anyways. I thin kI am gonna do this in increments and get a new FPR first and see how that goes. I didn't replace it with my S/C install, so I don't imagine it would be a bad option.... except on my wallet in this lovely !@#$ing economic doomsday. ;)

And speaking of which, going back to the air box, my ScanGauge relays that my fAI is about 20f cooler than it was with my CAI plumbed into the fender port. Some food for thought and means I am gonna have to, once again, head back to the drawing board. Not at all what I was expecting.

[WormGod]

Dag nebbit! CELs came back today after a stall just after startup. *sigh*

First it threw the 174 and then the 171. Looks like I am gonna go the o2 sensors route now. See if I can hunt down some bargains....

[VehiGAZ]

Gary, for what it's worth, I suggest you try a new MAF first instead of O2 sensors. Cleaning an MAF can help if you run a K&N, which will muck it up sooner or later, but MAFs just go after a while, in which case cleaning won't help. Your symptoms are consistent with the ones I had with a bad MAF last winter.

[WormGod]

Wallet allowing, I have a few things planned in the near future so that I can hopefully avoid any later issues.

Looking at replacing the o2 sensors, fuel pressure regulator, EGR, and I will take your advice on the MAF into consideration. I lost $8k in the last 3 months in the stock market so I am gonna be watching my spending a bit more closely so I can keep my nest egg secured. :eek:

[taylorRichie]

Just tripped the two codes on the way to the office this morning.

Based on this thread I'm thinking I should clean the MAF and see if that does the trick.

If it doesn't work out then, 02 sensors, FPR, and EGR? What about a PCV clean or replace?

Suggestions?

I'm only at ~52,000 miles. Also this is the first tank of gas I went with 85 octane instead of the normal 88 or 91, could the octane change cause a lean condition?

Thanks guys!

Richie

Glad I did the search and found this wonderful thread.

[tom4bren]

"could the octane change cause a lean condition?"

I'd say no but then everyone would beat me up so I won't.

I've always operated on the KISS principle when tracking down problems. Clean the MAS & reset the 'puter. If codes come back, try going back to higher octane & throwing in some gas treatment. If codes are still there, move onto FPR then EGR then O2.

[don moore]

i took out my mass air flow screen out ..like i did with my vette...Im glad we dont have checks here..

[VX crazy]

Today several times, I keep getting the P0171 code, I reset the scangauge since its not running any different....and it comes on within about 15 min of driving.....FPR Jay replaced for me awhile back....throttle body was cleaned last week when they did the timing belt and stuff.....guess I will clean the MAF and see what happens....AND I was on my way to get it inspected when it did this so I will try tomorrow

[VX crazy]

Interesting addendum.....I just swapped out MAF sensors off my other VX and noticed my rubber edging around my green filter is totally melted away, filter is 1/2 laying in the air box.....and I just had it out and cleaned and oiled it a couple weeks ago.....so it looks like I am on the hunt for a local green filter...

[blacksambo]

Just wanted to add my experince with 171 lean bank codes. I tried alll the above but was surprised to learn that it was leaky common chamber gaskets. Seems there's a service bulletin on these things being over-torqued from the factory. They should be 13lbs, or hand tight, anything more and the bottom one cracks and leaks air. Once I changed those gaskets, it was a new truck. It has never run smoother. To check your gaskets, start it up, and spray around the edge with carb cleaner. If it revs up slightly you've got a leaky gasket. Change it, you'll be glad you did.

[VX KAT]

Interesting addendum.....I just swapped out MAF sensors off my other VX and noticed my rubber edging around my green filter is totally melted away, filter is 1/2 laying in the air box.....and I just had it out and cleaned and oiled it a couple weeks ago.....so it looks like I am on the hunt for a local green filter...

I know it gets hot in Texas, but dang....:freek:

[Ldub]

I know it gets hot in Texas, but dang....:freek:

I was thinking more like....what'd ya clean it with...DRANO?...:laughing:

[VX crazy]

LOL I cleaned it with the cleaner for the green filter.....and rinsed it very well....but the rubber felt really weird before I cleaned it so I am thinking it is just too old.....hope that fixes my CEL so I can get it inspected today!

[Triathlete]

Lisa, don't they have a life time warranty like the K&N's? Might want to contact Green for a free replacement!

[VX crazy]

Thanks Billy, emailed them yesterday! I am using cheap paper filter in the time being!

[Triathlete]

No problem...in these times you can never save enough!:happyface

[WormGod]

My 171/174 woes have been intermittent for the past year. I ended up just learning to deal with staring at the CEL.

FWIW, I have no vac leaks and MAF cleansing never helps. Considered the o2 sensors but just never got around to it. In a sense, it's really not a big deal to me since I only drive it on Sundays, heh.

Well, it's been on for the passed few months straight and things are normal as ever. I gassed up yesterday and I recall when I was putting the gas cap back on, I had some difficulty just cause I simply wasn't lining the threads up well. Well, once on, I gave it the super duper annoyingly amount of turns and clicks. Just for good measure cause I felt like an idiot trying to get it back on. :p

Once back inside and ready to roll, I turned the key and imagine that.... the CEL was gone. I never made it home last night to check to see if a leaky or loose cap could cause a 171/174, but it went all last night without coming back on. Anyone know if a cap issue can cause these or if it throws a different code altogether?