Vargntucson

P0171 Code & Illegal Modifications to Exhaust System

I have a 1999 Toyota 4runner 4X4 Limited with a 170K miles. I’m the third owner and have put about 12K on the truck. Truck has been great so far.
The problem is I have the dreaded P1071 code and I can’t get the check engine light off to pass emissions.

I’ve cleaned the MAF sensor, used Sea Foam, and replaced the upstream 02 sensor. The previous owner replaced the downstream 02 sensor and MAF sensor. Although I don’t remember how many miles the two new sensors have on it. The downstream 02 sensor looks relatively new. The MAF sensor does not.

I have read a lot about this code but my situation is unique because I discovered my truck exhaust system has been changed (one less catalytic converter and Magnaflow added. When I replaced the upstream sensor I discovered that I’m missing a catalytic converter. My truck is setup to run under federal standards even though it was originally California. California has two Catalytic converters while the rest of the cars in the US have one. I discovered this when the upstream California 02 sensor plug wouldn’t fit and I had to go with the federal standard sensor. So basically my truck is illegal. I also have a K&N filter but I don’t believe I have over oiled it.
The big question I have is the illegal modifications setting off the check engine light because the MAF sensor is California or are they (MAF sensors) the same? When I first bought the truck I got the engine light to go off. Now it’s just on all the time. Comes on after 10-40 miles of driving.
I’m not sure what I should do now. Replace MAF sensor? Redo exhaust system (expensive!)

Texas_Ace

What does that code stand for?

Vargntucson

I'm sorry it's P0171 which is lean on bank 1.

Potential Problems for P0171
• Fuel pressure
• Coil packs (Replaced 2 years ago)
• Plugs (Replaced 2 years ago)
• Wires (Replaced 2 years ago)
• MAF sensor (Replaced by previous owner but not sure at what mileage)
• Rear O2 sensor (Replaced by previous owner but not sure at what mileage)
• Front 02 sensor (Replaced this week)
• K & N Air Filter (Replaced this week)
• Vacuum leak?
• Fuel pump
• Fuel filter (Replaced 3 years ago)
• Bad ECM
• Intake system (loose hose clamp around the intake silencer?)
• Replace #1 Fuel injector (injector $150)
• vacuum leak in the PCV (Replaced PCV a year ago)
• PCM Powertrain Control Module (I don’t what this is?)

TheDurk

MAF sensors are the same. The front O2 is a wideband air/fuel sensor, the cats are different, and the engine ECU is different--that's about it. If you feed a federal front O2 sensor signal that is totally different electrically into a Cali. ECU I would think you would get a lot more codes than p0171. I can't imagine the engine would run well at all, or even get into closed loop. Is the ECU original? Is this hack-up recent, as far as you can tell? Finally, are you absolutely sure the truck was born a Cali.? Could we see a pic of the emissions sticker under the hood?...They can be confusing.

Bullet22r

replace the K&N filter with a stock one, the oil from it will contaminate your MAF sensor.

Texas_Ace

Your not supercharged are you?

2Whlin

I disconnect my battery and the code goes away for a few day's while I get an inspection.

TheDurk

That doesn't work in stricter states where they plug into the computer and ding you for any tests not complete (like NJ where I live).

Vargntucson

I wish it was super charged but it's not.

2Whlin

well, not sure? All I know is I have code for bad catalytic converter and this works for me every time..

Vargntucson

I finally broke down and took my 4runner to a local mechanic recommended by a friend. He discovered a small vacuum leak on the condensator. The mechanic just tood it out. The condensator I have was installed by the previous owner. I checked out the website (http://www.condensator.com/) and it’s basically a supplementary carburetor that sucks the sludge out of your engine and pre-cleans your fuel for improved performance. Does anybody know anything about these condesators?

So the theory is the condensator was causing the P0171 code to be thrown. Truck seems to be running better so I’m not sure if it’s solved. I have 30 miles on it so far. I’ll give you guys an update once I get some more mileage.

Vargntucson

Yeah that was my first thought until I did a little research and found that there were people who had K&N filters and didn't have any problems. Although I do believe that a lot of codes are thrown by K&N filters that aren't properly maintained.

TheDurk

It works because this is the rule in Texas:

http://www.txdps.state.tx.us/rsd/vi/...SystemsChecked

This is not the rule in NJ, NY, CA and many other states. Enjoy it while it lasts.

New Jersey's rule:

http://www.nj.gov/dep/bmvim/NJ2010_Annual_Report.pdf

Vargntucson

Here is a pic of the emissions sticker. I'm pretty sure it's california although I don't understand why it says Fed & Canada at the bottom.

2Whlin

dam gobernment!!

Mtn Mike

iTrader: (1)

I had this code a few years ago. After I had chased down vacuum leaks, and checked the MAF and O2 sensors, the code still popped up. Finally, the Yota dealer service department replaced the Throttle Position Sensor. What do you know, it worked, and wasn't very expensive either. You might want to try that.

dazbert

That's not a Cali vehicle. My 99 has CAL & OTC instead of FED & CANADA at the bottom, and there's more text in the main box.

TheDurk

What he said, and what I suspected. There was no way that truck would run well with a mismatch between ECU and front O2 sensor. As I said, those labels can be confusing. P0171 is a pain to isolate, but at least you aren't chasing ghosts.

I'm amazed I didn't see the label before, but you posted it exactly at the same time as my last post.

Vargntucson

Engine light is off! No engine light with 150 miles and I cleared emissions this week so I'm good for the next two years. Mechanic replaced the MAF sensor. And yes those emission stickers are confusing.

Pretty cool site I found thanks to Shax that decodes your vin#

http://www.decodethis.com/