P0171 and P0174 (1 Viewer)

[HomersCanyonero]

@07GX470 Are your P0171/P0174 codes on all the time? Or they intermittently go away for hundreds of miles and then they come back?

I had searched several forums for information on these codes and found this information. For what it's worth:

Common Problems That Trigger the P0171 and P0174 Code (not in any particular order):

1. PCM software needs to be updated
2. Vacuum leaks (Intake Manifold Gaskets, vacuum hoses, PCV hoses, etc.)
3. Mass Airflow Sensor (MAF)
4. Plugged Fuel Filter or weak Fuel Pump
5. Plugged or dirty Fuel Injectors
6. Air Intake Control Valve No 2; Toyota Part # = 17320-0A010

One guy in another forum (in ClubLexus on an RX330 forum) was adamant that #6 "air intake control valve #2" solved his issue with the P0171/P0174 after almost replacing all the emission components. He explained that the cracked control valve was letting air in at idle, so he would get the P0171/P0174 when he idled too much, but not on the freeway at speed.

Anyways, as far as the P0420/P0430 codes morphing into or causing the P0171/P0174 codes, I just don't know. I would tackle the P0171/P0174 codes. My problem is intermittent and I haven't seen it in 13 days and over 500 miles, so the MAF sensor cleaning had an impact since it's taking longer for the codes to show up.

 

[GonzoShinyPants]

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

Hi Bernardo, no confusion on my part about what you meant with the O2 sensor spacers - in fact I see they are marketed as being for the purpose of removing dashboard warning lights. But by using those spacers you are obviously manipulating the oxygen detected and therefore affecting how the whole system is adjusting the rich/lean fuel/air ratio. But you mention you assume the P0420 and P0430 (Catalyst System Efficiency Below Threshold) codes mean it's too rich. It may or may not mean that - it could mean too rich or lean, but either way that the cat was functioning below a minimum efficiency rating (which of course is just a number/rate programmed into the computer, based on pollution laws or whatever).

Because the fuel/air ratio is constantly cycled back and forth between rich and lean it makes sense to me that if that system has problems you could get codes indicating both too rich or too lean.

Either way, I'd still remove the o2 spacers just to see if your MPG improves. The system is mainly for pollution control so if you can improve MPG only you are still technically reducing the vehicles pollution and if it works otherwise I don't know if I would spend the money.

I have some regret about dropping $1k on the recent issue I had - while I want to reduce pollution as much as possible, as I've come to understand what was going on, it's likely the entire secondary air intake is a relatively small part of the emissions reduction and if I had to do over I would more seriously consider the bypass option.

 

[HomersCanyonero]

Re: I have some regret about dropping $1k on the recent issue I had - while I want to reduce pollution as much as possible, as I've come to understand what was going on, it's likely the entire secondary air intake is a relatively small part of the emissions reduction and if I had to do over I would more seriously consider the bypass option.

Yeah, there's an affordability part with fixing emission issues. I have my limits on how much I can spend fixing these emission problems.

In terms of my MAF sensor cleaning, it didn't work in terms of fixing the P0171/P0174 codes. This week on 3/05, the CEL came on. I checked the codes and they were P0171/P0174. I cleared them and cleaned the MAF sensor one more time. I've used about 60% of the cleaner in the CRC can. The CEL came back the next day on 3/6 when going off-roading up in the hills. I cleared the said codes and it hasn't come back in a couple of days, so I will need to do the smoke test to see if there's a leak somewhere.

 

[Arailt]

Hey Homer, did you ever figure out the P0171 code? I got it randomly this morning.

 

[HomersCanyonero]

Cleaning the MAF multiple times did help. I haven’t had P0171 or P0174 in over a year.

 

[Arailt]

Cleaning the MAF multiple times did help. I haven’t had P0171 or P0174 in over a year.

Nice. That's good to hear. Thanks, Homer. I cleaned my throttle body and MAF and installed a new air filter. I'm keeping my fingers crossed it doesn't come back.