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!

[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.