P0171 and P0174 (1 Viewer)

[HomersCanyonero]

These codes keep coming back too quickly after resetting them. I'm afraid to tackle this problem since it seems there's endless possible issues.

P0171 = Fuel System Too Lean Bank 1
P0174 = Fuel System Too Lean Bank 2

My mechanic thinks it's the MAF sensor based on his diagnostic machine. In order to be sure, we wants to do some type of colored smoke test.

I did some research on ih8mud and someone else had the P0171 and P0174 and their issue what the intake air control valve #2 part number 17320-0A010.

I'm not sure how to tackle this problem. My 2003 GX470 runs great and I have no issues when driving around town or in the highway. MPG is good since I put 40 PSI on the tires.

Any ideas?

Things I have done in the last 6 months to the emissions system:
1. Replaced both O2 downstream sensors with Denso ones
2. New Toyota gas cap
3. New Denso Iridum spark plugs

Other maintenance done in 2017:
1. New Denso radiator, Aisin water pump, Mistubosho timing belt, Bando drive belt, Toyota upper/lower hoses
2. New Denso alternator
3. New Lexus battery by Interstate
4. New fluids all around including transmission, brakes, engine, TC, and diffs

So, this GX470 has been babied and it's crapping codes on me.

 

[tlin]

A friend did a smoke test not too long ago which helped isolate a poor seal on his air intake hose - also had lean fuel codes (GM truck, was driving him nuts), can't hurt to go that route before buying parts. My $.02.....nothing else comes to mind other than a vacuum leak somewhere on the intake side.

 

[HomersCanyonero]

Thanks. First time that I think blowing smoke is the right thing to do.

 

[HomersCanyonero]

The check engine light went off on its own. It's been 3 days and I haven't seen it come back. Not sure what happened. I didn't clear it this time. I was going to take it in to blow smoke, but codes are off. Let's see how long they last off.

 

[GXO]

Sticky MAF makes a lot of sense.

 

[HomersCanyonero]

Okay. I went on trails to the talc mines by red rock state park, burro Schmidt tunnel, randsburg living ghost town, and Bickel camp and my check engine light went on after driving 100 miles to the trails.

I’ll get the MAF sensor replaced this weekend.

 

[07GX470]

I’ll get the MAF sensor replaced this weekend.

Did this cure the problem?

TIA
Bernardo

 

[HomersCanyonero]

I ended up flying away on a trip for a month and didn't get to the mechanic prior to the trip, so I did not replace MAF sensor as planned. I just got back and CEL has been off for 3 days/100 miles.

I'll report back when I do change it.

 

[lgrt]

you should be able to clean your MAF sensor... that is an easy 1st step. this video is based on a FJ Cruiser's V6 but will give you the basics

 

[HomersCanyonero]

Awesome video. Seems easy enough to try to clean. You probably don’t even need to take the whole air unit out. Just disconnect and unscrew, clean with electrical cleaner, and reconnect. Hmmm maybe I’ll try that soon.

 

[HomersCanyonero]

My GX470 seems to know when I’m going off-road and it throws the P0171 and P0174 as I’m driving to my off-road destination. It stays on the whole two days I’m in Anza-Borrego Borrego. I come home and the next morning the CEL is gone and it’s gone for two days.

Anyways, I cleaned the MAF sensor today. It took less than 10 minutes not including the 5 minute wait time to let the cleaner dry.

I’ll find out if this worked or not in a week or so.

 

[HomersCanyonero]

So far, the MAF sensor cleaning is good. I took an offroad trip to the Mohave Desert and the codes did not come back. That was more than 200 miles including freeway and 4x4 on lo for two days. Let's hope the cleaning worked, but I need to wait a few more days.

 

[07GX470]

Thanks for reporting

 

[HomersCanyonero]

Well my results are not fully conclusive. After cleaning the MAF sensor on 2/16 and driving over 350 miles off-road, freeways, and city streets, the CELs came back briefly last Saturday 2/24.

I didn’t have the code reader with me, so I drove about 20 miles with the CEL lights on. The next morning I started the GX470 to check the codes and the CEL lights were gone on their own. I’ve driven 3 more days and 75 more miles and the CEL is still off as of today 2/27.

So, I can’t say that cleaning the MAF sensor solved my problem with certainty. I’ll have to wait more to see if the CEL lights come back and if I can read them to see which code it’s throwing. It could be a different code.

Anyways, I’ll keep reporting for those that might be thinking of cleaning the MAF sensor to resolve the P0171 and P0174 codes.

 

[GonzoShinyPants]

I recently had CEL and the 3 VSC/skid lights come on. The code was P1441, which is a secondary air intake system air pump control valve stuck open. One solution as posted on this forum is the use of a bypass kit. However, it appears that may be illegal in some states and regardless I did not wish to undermine the emissions control system and cause the truck to pollute more than it does.

To quote Wikipedia about what this does, because I'm kind of fascinated with all the emissions control tech (despite the problems it gives us):
"As emission control strategies grew more sophisticated and effective, the amount of unburned and partially burned fuel in the exhaust stream shrank, and particularly when the catalytic converter was introduced, the function of secondary air injection shifted. Rather than being a primary emission control device, the secondary air injection system was adapted to support the efficient function of the catalytic converter. The original air injection point became known as the upstream injection point. When the catalytic converter is cold, air injected at the upstream point burns with the deliberately rich exhaust so as to bring the catalyst up to operating temperature quickly. Once the catalyst is warm, air is injected to the downstream location — the catalytic converter itself — to assist with catalysis of unburned hydrocarbons."

And HomersCanyonero the reason I bring this up is if you are getting "fuel system too lean" codes you may experience worse mpg (though you say that seems ok), reduced power, worse emissions output or all of that. Once the cat is warmed up, as you may know, the O2 sensors constantly check upstream and downstream oxygen levels, related to how rich or lean the fuel/air mixture is, and adjust the mixture back and forth to maintain maximum catalytic converter efficiency, while also taking into account engine power and fuel efficiency (and operating at whatever ideal ratio of those 3 the manufacturer came up with).

Just some info from my recent repair and what I have been trying to learn about. Hope it's of some help if the lights come back.

 

[HomersCanyonero]

Okay, thanks @GonzoShinyPants. I'm not getting the P1441 code from the previous readings that I took with my ScanGauge II. Also, I have a 2003 GX470 which doesn't have the secondary air intake (at least I think that was introduced in 2005 GX470).

Anyways, my 2003 runs smooth and it has very good gas mileage. On the freeway going 65 mph per the Waze app, the computer shows that I'm getting 18.6 mpg. This is without adjusting for the bigger 32.6" tires.

So, in my case, it looks like the problem is between the MAF sensor or the air intake control valve #2. Right now I'm going after the MAF sensor because it was an easy repair to clean it. Next I might have to look at the air intake control valve #2.

 

[07GX470]

I recently had CEL and the 3 VSC/skid lights come on. The code was P1441, which is a secondary air intake system air pump control valve stuck open. One solution as posted on this forum is the use of a bypass kit. However, it appears that may be illegal in some states and regardless I did not wish to undermine the emissions control system and cause the truck to pollute more than it does.

To quote Wikipedia about what this does, because I'm kind of fascinated with all the emissions control tech (despite the problems it gives us):
"As emission control strategies grew more sophisticated and effective, the amount of unburned and partially burned fuel in the exhaust stream shrank, and particularly when the catalytic converter was introduced, the function of secondary air injection shifted. Rather than being a primary emission control device, the secondary air injection system was adapted to support the efficient function of the catalytic converter. The original air injection point became known as the upstream injection point. When the catalytic converter is cold, air injected at the upstream point burns with the deliberately rich exhaust so as to bring the catalyst up to operating temperature quickly. Once the catalyst is warm, air is injected to the downstream location — the catalytic converter itself — to assist with catalysis of unburned hydrocarbons."

And HomersCanyonero the reason I bring this up is if you are getting "fuel system too lean" codes you may experience worse mpg (though you say that seems ok), reduced power, worse emissions output or all of that. Once the cat is warmed up, as you may know, the O2 sensors constantly check upstream and downstream oxygen levels, related to how rich or lean the fuel/air mixture is, and adjust the mixture back and forth to maintain maximum catalytic converter efficiency, while also taking into account engine power and fuel efficiency (and operating at whatever ideal ratio of those 3 the manufacturer came up with).

Just some info from my recent repair and what I have been trying to learn about. Hope it's of some help if the lights come back.

Thank you,
both @HomersCanyonero and @GonzoShinyPants , for reporting back, and for all the details.

I´m specially interested in what might cause the "fuel system to lean" codes.
My story started back in may last year, just days after I bought the GX, with a P0420 and a P0430 (Catalyst System Efficiency Below Threshold).
So I swapped both O2 sensors with new ones, cleaned the codes, but got them back just a few miles down the road.
Next I ordered both Denso AF sensors, replaced them, and was then greeted with a P0171 (System too lean).
Cleaned the MAF, checked all cables, ground etc. without success.
Finally bought a pair of adapters (like those: https://www.amazon.com/S2-Industire...eywords=check+engine+light+eliminator+adapter), to move the O2 sensors out of the stream a little bit, which finally stopped the codes from coming back.

No codes for the last six month, but I'm feeling bad for cheating.
14 MPG average. Now, with the recently added BFG 285/70R17, it´s even worse.

Any suggestions?

TIA
Bernardo

 

[HomersCanyonero]

In California, there's a visual inspection of the the emissions system when testing is required by the state to register, so those extensions would not work too well here. They would be detected by the emissions person running the test. Moreover, I used to suffer from lung pains back in the late 1980s in the horrible smog in Los Angeles. As much as it pains me to pay and troubleshoot for the emission issues...it's the right thing to do. I remember those days when you could see a brown layer of smog in the LA skyline.

It's interesting that you mention that you started with a P0420/P0430. The day I went to get a smog to register my 2003 GX470 in early 2016, I think I got a P0420. I replaced the two downstream O2 sensors with new Denso ones and my problem went away and I was able to pass smog.

A year later, I'm getting the P0171/P0174. It comes and it goes. It was more frequent prior to the MAF sensor cleaning, but right now it's been off on its own (including the the time it came on and turned off on its own) for over 500 miles and 12 days.

If it comes back, I need to check the codes. I'm carrying the ScanGauge II with me, so I can check. If they are the same codes as before, then I'm going to clean the MAF sensor one more time (since it's so easy) and then I'll wait. If it comes back, I will get the smoke test done to see if there's a leak somewhere. I don't want to replace parts unless I know exactly what's wrong.

Anyways, emission issues are expensive and hard to fix and I'm seeing them on several of my cars and my kids cars. They are young college grads and they still drive the hand-me down cars (1996 FZJ Landcruiser, 2004 Acura MDX, 2010 Prius (no issues on this one)). Yeah, my son doesn't want to get rid of the 96FZJ with 250K miles.

 

[GonzoShinyPants]

If you read the full article about catalytic converters linked in my last post there is some explanation about oxygen sensors and how the system oscillates between a rich and lean fuel mixture. Ultimately it seems the worst case is increased pollution and reduced fuel efficiency but I don't think you are hurting the engine necessarily. Like HomersCanyonero I wanted to retain the best pollution control on the vehicle from a personal standpoint. But I did just drop $1k on replacing the 2 SAIS control valves (though after seeing the parts it certainly appeared one was quite dirty and the other looked new, but due to high labor I had told them to replace both just in case) so it's not cheap to do these repairs. Reading that Wikipedia article makes you understand that it's a very precise setting the system is set to work at and if anything goes wrong you get CEL, codes, etc.

So @HomersCanyonero I don't think I would sweat it too much at this point if you are both getting good mpg and the codes are not consistently on. I think it's possible the rich/lean ratio is moving out of the programmed range on occassion, thus you get the codes, and then moving back in, thus the lights go away.

Bernardo for the fuel system too lean codes what that appears to me is there is too much oxygen relative to the fuel in the mixture coming out of the exhaust manifold and/or into the cat. The initial cat system below threshold was probably just an indication of the same problem. Since you have an '07 you probably(?) have the secondary air intake system as well, like I do, but obviously you're on a witch hunt at this point and that's annoying and expensive. But with mpg that bad it might be worth pursing further. We noticed reduced fuel efficiency with the issue we had and our mechanic noted a large amount of gasoline in the parts he removed. From what I understand the oxygen sensors are the key part that regulates the fuel/air ratio. I think I would try removing the spacers and seeing if your mpg improves first of all.

Best of luck - I'm sure you guys hate these codes/issues as much as I do! All of this just to burn dino juice a little cleaner. Oh well, I guess we need to!

 

[07GX470]

Maybe it is the language barrier on my side, (native German, long time Spanish speaker, no English practice for 25 years), so please forgive me.
In no way was I suggesting those spacers to remedy the problem. At the time, it was a cheap, temporary way (for me), to get rid of the codes.
With this out of the way, back to the problem:

What I don´t get is, that a problem, that started out with a P0420 and a P0430 (Catalyst System Efficiency Below Threshold), which leads me to believe that to little or no oxygen was detected past the cat (to rich), turned into a P0171 and a P0174 (System too lean), after nothing else but swapping out the AF sensors.

So, what should I try next, without throwing tons of money at it?
Any recommendations?

TIA
Bernardo