CEL, P0171, help?

CEL on 2010 with 218k recently came on, scanned at 2 stores both showing P0171 (system too lean). Tried a can of MAF sensor cleaner, to no effect. Fuel economy now running about 10-15% below normal. Car also hesitated for the first time ever when I floored it to pass another car.

I watched Nutz About Boltz's throttle body cleaning video, and'll certainly try that. And read somewhere here about the recommendation to replace PCV valve (Patrick Wong, I think?) I've also read some interesting threads on other Toyota-related sites with good info. I'm starting to think the diagnosis and fix for this may be beyond my capability, but I just would like to make sure I'm not heading to a mechanic or dealer to have them do something I could do myself.

 

DENSO 234-9090 right?
If not, does anyone know the OE part number?

 

Or where it is? A photo would be cool.
At TIS the TIS FAQ says Windows is required. Has anyone used a Mac to download stuff from TIS?

 

Thank you so much, Mike. YOU ROCK! I put some PB Blaster on the sensor, went to use my brand-new O2 socket, and quickly discovered that it wasn't gonna happen without grinding.
Also took the hose off the PCV valve, but had to put it back on. The valve just laughed at my implements.
Soon.

Shawn

 

I forgot to mention that I replaced the Mass Air Flow Sensor, and when I did, I forgot to reconnect it, which is what caused the hesitation when trying to pass with WOT. Also, at some point, I noticed the ICE is on a lot more than normal. The drop in mileage seems like it could be attributed almost entirely to this fact.

In any case, after replacing the upstream Air/Fuel Sensor and the PCV valve, I saw no change in the poor fuel economy I was getting. Nor was I able to get the CEL to stay off. After clearing the code, it would always come back. Sometimes it would take over a hundred miles before it returned, but it always did.

I got a scanner that does live data, and, as an untrained beginner, the only thing I really noticed was that the long term fuel trim was always extremely high, apparently maxed out, actually, at 39.8%. Short term fuel trim varied plus or minus in a normal range (often around 0, but no more than 10% or so either way). I'm guessing that the code gets thrown when the STFT and LTFT both add up to a specific value.

So, with my inspection due in a few short weeks, I broke down today and ponied up at a dealership for diagnostics, figuring maybe Toyota-trained techs and all that costly Techstream equipment and/or factory manuals could make the difference and solve the problem where a trusted independent garage had failed. By the way, that garage smoked the intake looking for vacuum leaks (didn't find any), looked at the inside of the throttle body (which they said looked spotless), and graphed the oxygen sensor output. (In their final analysis, they thought it was the oxygen sensor.)

The dealership service manager told me that the problem is the "vacuum switch valve", a part they didn't have in stock. He said there is a service bulletin that references my code and/or problem, and, although somewhat counter-intuitive, replacing this part will fix the issue I'm having. The figure quoted for the fix was just under $400 (part and labor), from which the $120 diagnostics charge would be deducted if I have them do it once they get the part in. After a cursory look online, I'm not really sure I know what part he's talking about, but if I'm searching correctly it looks like the part runs about $50 or $60 and up. What's worse is that after looking for the TSB he mentioned, I can't find anything more than a summary. (I'm guessing it's #TSB-0041-15, NHTSA Item Number: 10058418) Does anyone have access to TSB's? Or know what the "vacuum switch valve" he's talking about is?

 

In case you're interested in what sort of trouble you might encounter past 200k, I continue this saga:

Yesterday, the service advisor confirmed that TSB-0041-15 is the TSB they thought was relevant. I've tried to upload a PDF of the actual TSB to this site, but I think my slow internet speed might be preventing that. For now, it's here: T-SB-0041-15.pdf - Brought to you by View Docs Online

So the TSB states: "may exhibit a MIL “ON” condition with DTCs P0A0F (Engine Failed to Start), caused by Purge VSV/PCV line separation from the throttle body housing. One or more of the following DTCs may also set: P3190, P3191, P0171" The problem is that I've never had a "P0A0F (Engine Failed to Start)" code. So the wording indicates this TSB doesn't even relate to my code (P0171). The dealership people just thought it did. Am I right in thinking that?

The first part of the repair procedure is this:
"Inspect for proper installation of the PCV hose and Purge VSV vacuum line at the throttle body. Ensure the vacuum line is secured at the Purge VSV. If all lines are properly seated, this bulletin does NOT apply. Follow normal diagnostic procedures per the Repair Manual."
I don't see anything unusual when I check those hoses. Maybe it's a hairline crack?? I wonder how this would've played out if I had agreed to pay almost $400 for the service they recommended???

I'm not sure what to do next. Any opinions or comments are welcome.

 

Thanks, Mike. You know, the worst part is the reduced range and having to fill up more often. I've been running about 15-20% below normal mileage for about 12k now. I don't really think it's affecting my cat, though, because the biggest problem seems to be that the ICE is just on more than normal. Having watched the HSI for over 150k before this issue appeared, I have a good sense of when it is supposed to turn on and off and it's definitely on a lot more now. To answer your question: no, it doesn't consume oil. As I mentioned before, the LTFT seems maxed out. Watching the live data while driving with a scantool attached, I've seen it go from where it usually is at 39.8% to 39.1%, but then it almost immediately goes back to 39.8%.

I erased the P0171 a number of times, but aside from the codes resulting from my forgetting to reconnect the MAF cable early on, I've never seen any others. Especially not P0A0F (Engine Failed to Start), which TSB-0041-15 mentions. From the wording of that document, I just can't believe that it relates to my issue. But how can I explain that to the service advisor, along with how I think that they charged me for diagnostics when all they appeared to do was scan my code and decide an inapplicable TSB was applicable? I wanted real diagnostics!!! What's he going to say? "Sure, come back in. That'll be another $120, please." I almost want to call Toyota and tell them how displeased I am. I'm not sure I'm calm enough to do that yet.

Interesting to read the original TSB you posted. Thanks again.

 

[Here's the TSB uploaded here on PC, instead of at the site I linked to above.]

 

Good advice. The service advisor mentioned they found the P0171 that I already told him about, but he didn't mention that they found anything else. I'll ask him to verify. My scan tool is limited. I'm kind of thinking injector issue(s), but I'm such a noob that I'm not a great chaser/tracker. (Hence the hope the dealership could tell me what's wrong.)

I did see the part the dealership would've replaced available online for $9.99 (Denso, used, from a low mileage Toyota). I'll throw that in, but I doubt it will make much difference. That would be cool if it does. I'll know my money was well-spent at the dealership. Most people would say it's irrelevant, but when googling for the dealer's phone number I discovered that the owner of the dealership held a fundraiser at his mansion for Trump at the end of August.

 

The invoice only mentions the P0171. I was actually surprised how little is on there. The number "120" appears five times (or six if you include my stapled receipt). But I'm not bitter or anything. It does mention the reflash they did for the E0E safety recall, although querying my VIN on TIS doesn't show that's been done.

I ordered the mini VCI. I'll have it Wednesday. I'm looking forward to doing things with it that I never thought I'd be able to do. I recently downloaded a bunch of stuff from the service manual on TIS, but I skipped a bunch of stuff since I didn't think I'd ever have Techstream-ability. An exciting prospect.

Yes, MAF was replaced with the new factory Denso part. Plugs were replaced with SC20HR11 at 129k so they're now at 101k, although they were at 88K when the problem appeared.

I stay away from unbranded gas, and I got a six-pack of "Chevron PRO-GARD Fuel Injector Cleaner with Techron" back in August after reading some Gen II threads. Tried another bottle today with no detectable change. I'll look for some Techron Concentrate Plus. And I'll clean the TB. Also, some swear by it, others swear at it, but I got my first bottle of Seafoam recently. I haven't used any on the car, but I definitely will on some of my 2-stroke stuff. If I was sure that dirty injectors were the issue, I think I might try MotorVac service. The mini VCI is my only hope to know what's really going on. That reminds me of Star Wars when Leia pleads with Obi-wan for help in the little holographic message.

My scan tool does display o2 data. I even graphs it, but it's fairly rudimentary. I just discovered it graphs a few other things, too. Not all the o2 capabilities of the tool are available for my car. Again, I await the mini VCI. I watched the fuel trims a little more today when I was driving (at different RPMs). The LT never moved from 39.8%, although ST goes plus and minus.

I did the PCV valve when I did the A/F sensor. I guess later this week I'll be able to do real inspection mode. I never smell any exhaust, but I guess it's possible.

Among the documents I downloaded from the service manual are the ones related to the injectors and fuel pressure system. If that's what the issue is, I will definitely consider doing it myself.

I began to fantasize about trading the car and getting a PIP. I really can't justify it, though. I really love my car, I just wish it was getting the mileage it's supposed to! (Well, that and I wish it would pass inspection.) I keep thinking how great it is that our cars still get 40+ mpg even when they have fuel delivery/air issues. If my car is still less emitting than the vast majority of cars that do pass inspection, doesn't that mean I should pass, too???

 

Finally got the MVCI and connected today. I spent some time getting a feel for the software, then replaced the vacuum switch valve that the service advisor claimed was the cause of the car's problem. I never really suspected it was the cause, but it was only 10 bucks. After installing the new VSV (the one under the air cleaner box), I took the car for a drive. Didn't notice any significant change, especially to the long term fuel trim I was hoping might come down, so I disconnected the battery for a minute to zero the LTFT. Within a minute or two, the number had returned to the 30's. How can I tell the dealership that what they call diagnosis seems to consist of guessing that a TSB that mentions my DTC is the solution to the problem? I guess I'm just not ready to kiss my $120 goodbye. And if I do, what might I do next? I haven't done the throttle body yet. Or the plugs. I did check for exhaust leaks while in inspection mode, but didn't find any. I was surprised at two things in that department: 1) the exhaust pressure at the tailpipe is lower than I expected. 2) I also never noticed how the engine purrs with the hood open. I did wonder if I was hearing an extra sound, though. That's my problem: I'm not a mechanic. I just play one on TV. I tried to pay a dealer to have a real mechanic tell me what's wrong, but that plan has so far failed epically. And my inspection is due in 4 days. Anyone?

 

Forgot to post this: Techstream says the range for the A/F sensor is abnormal.

 

Thank you very, very much for that. I'll take a look.