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Discussion Starter #1 (Edited)
A month ago, son's 2002 Echo started showing the CEL. Had a scan done at Autozone and the P0171 code came up.

After doing some research, we bought a can of MAF cleaner and disconnected the battery cable, sprayed the sensor down, waited for it to fully dry and reinstalled it. My son started the Echo, backed out of the spot, shifted into Drive and then got no response from pressing the gas pedal. Turned off the engine, turned it back on, and the CEL came on again. But this time, the car had no problem responding to gas pedal pressure in Drive. And until tonight it didn't happen again.

With the CEL light still on and my son needing to have his emissions test done, tonight we attempted once again to fix this P0171 issue. Hoping that maybe we had done an inadequate job of cleaning the MAF sensor the first time, we once again tried the same procedure. And once again, after starting the car immediately following reinstallation of the sensor, he backed the car up and then no received no response from the gas pedal after shifting into Drive. Turned off the engine, turned it back on, CEL came on and then problem with the gas pedal disappeared.

I can't tell if this is the sign of a bad MAF sensor or instead a sign the part is actually working correctly and reacting to another problem. I would assume that a bad sensor would introduce the fuel flow issues on a more consistent basis, but then again, this has only appeared immediately following a sensor clean. Any thoughts here? I'd rather not purchase a replacement sensor unless we can be assured it will fix the issue.

Any guidance is appreciated.

Best regards,
Mumford

* Edited to correct code #
 

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Discussion Starter #5
That is a lean burn code, could be a lot of things, not just MAF. Search the code. I'll comment more later.
Understood. It seems to be the most offered suggestion for dealing with the code, so we tackled that first as a possibility. I just don't want for my son to eat the cost of replacing a part he might not need. So I was just curious if the lack of response from the pedal immediately following a cleaning of the MAF Sensor is a common indicator of a faulty sensor.

If not, I would tackle other possibilities such as cleaning fuel injectors, checking vacuum hoses, the O2 sensor, etc. before plunking down cash for a new MAF sensor.
 

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puddleglum2
2000 Toyota Echo
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P0171 Code

I had the same code on mine when I bought it. Unfortunately it is one of the codes that identifies a problem and not a faulty component. Here is a link to my thread on the code.
https://www.toyotanation.com/forum/26-yaris-scion-ia-vitz-echo-forum/1403729-p0171-lean-burn-code-questions.html There are others if you use the search function.
Here is a link to a manual with good info on this code, a sequence of testing and how to test components.

In my case, after trying to clean the sensor along with several other things, I changed the sensor and it solved the problem. That doesn't mean yours is bad though. I also had the code only showing up intermittently. It has to see both short and long term fuel trims out of range to set the code from what I understand. I never had a loss of throttle though. Not sure if the MAF being out of range would cause that, maybe if it wasn't reconnected properly but not sure. Thinking back in it though, the engine ran really bad after cleaning the sensor for the first several miles. I thought it had more to do with disconnecting the battery and the computer losing its memory.
Do you have a code scanner? If not, I would start by ordering a Bluetooth adapter (they're cheap) and downloading a good diagnostic app for your phone. I use Torque for Android, just the free one, but the full version is better. There are others that work with Iphone I think. Point is you need to be able to see what your engine is doing when the code sets to help determine what is causing the code to set. Also, take a really close look at all your vacuum lines, your PCV valve and spark plugs. Any vacuum leak or a misfire can cause it. Hope this helps.
 

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Discussion Starter #8

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puddleglum2
2000 Toyota Echo
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Good. Choose an app like Torque that allows you to set up gauges on your phone or tablet. Only Torque Pro can track LTFT and STFT, free one is only STFT. Watch closely when the readings go out of range. At idle is more likely a vacuum leak. Higher RPM's is more likely the MAF or maybe a fuel issue. Set up a gauge to see if your O2 sensor switches properly. It should bounce up and down. If it sticks when all the other readings are normal, it could be that. If you think it could be fuel, I would start with a good injector cleaner like Redline or Techron before spending a lot on professional services. Can't hurt right? Hope you find it easily.
 

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Yes, both times we cleaned the sensor.

I've taken puddleglum's suggestion and have ordered a bluetooth OBD unit.. Hopefully that will allow me to properly diagnose the problem.
Good. Choose an app like Torque that allows you to set up gauges on your phone or tablet. Only Torque Pro can track LTFT and STFT, free one is only STFT. Watch closely when the readings go out of range. At idle is more likely a vacuum leak. Higher RPM's is more likely the MAF or maybe a fuel issue. Set up a gauge to see if your O2 sensor switches properly. It should bounce up and down. If it sticks when all the other readings are normal, it could be that. If you think it could be fuel, I would start with a good injector cleaner like Redline or Techron before spending a lot on professional services. Can't hurt right? Hope you find it easily.

@Mumford67

Hey, just wondering if there was any update?
 

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Discussion Starter #13
@Mumford67

Hey, just wondering if there was any update?
Okay....finally have an update after all this time. Took a while due to schedule conflicts to get together with my son. Got the scanner in his car and linked it with Torque.

Car idles at approx 721.8 RPM. When idling the STFT reads at -3.1%, the LTFT reads at 40.6% and the MAF reads 1.5g/s. If we push the accelerator till we are reading around 2,600 RPM, the STFT climbs to 1.6%, LTFT drops to 36.7% and the MAF climbs to 5.8g/s.

O2 numbers sit at about .2V when idle and fluctuate up and down between 0.1V and 0.7V when at the higher RPMs.

I have attached screen captures of full stats at both RPMs as reference.

Any thoughts here?
 

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if no intake or exhaust leaks, I would say 02 and poss MAF. I seem to recall that the 02 sensor voltage should still fluctuate at idle, not just at 2k RPM. So, I would do 02 sensor(s) first and if nogo, then the MAF.
 

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Discussion Starter #15
if no intake or exhaust leaks, I would say 02 and poss MAF. I seem to recall that the 02 sensor voltage should still fluctuate at idle, not just at 2k RPM. So, I would do 02 sensor(s) first and if nogo, then the MAF.
I'll recheck the O2 sensor readings this weekend just to make sure I didn't miss anything. However, if my original readings are consistent, I will start with the O2 sensor and go from there.

Thanks for the advice.
 

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sure thing. i forgot which one..but bank x is precat bank y is post cat..just double check to see which is which if replacing just one so you do the right one.good luck.try to stick with denso.
 

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Discussion Starter #17
sure thing. i forgot which one..but bank x is precat bank y is post cat..just double check to see which is which if replacing just one so you do the right one.good luck.try to stick with denso.
Thanks...one more question, if you don't mind. If I find that my first O2 sensor numbers were misread, and that the new O2 readings do fluctuate in idle, do you think it still makes sense to tackle the O2 sensor(s) first, or should I replace the MAF sensor first?
 

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Yeah I would tackle the 02 sensor first. They generally are less expersive than the MAF by $20 or so. Buyautoparts(dot)com has them, they are usually are re-boxed denso, at least their fuel injectors are. Plus, you cleaned the MAF, so unless it's gone, id check less expensive things first. Worst case in the end (semi-optimally) would be you ended up replacing the o2 sensor and eventually the MAF.

This is another thing you can do to eliminate if MAF or not:
If you know someone with one of the following vehicles, when they aren't looking steal their keys, and pop the hood and steal their MAF.....Or you could just ask them....(I suppose that's better..I guess..)

LEXUS ES300 (2002 - 2003)
LEXUS ES330 (2004 - 2006)
LEXUS GS300 (2001 - 2006)
LEXUS GS430 (2006 - 2007)
LEXUS GS450H (2007 - 2011)
LEXUS IS300 (2001 - 2005)
LEXUS LS430 (2001 - 2006)
LEXUS RX330 (2004 - 2006)
LEXUS RX400H (2006 - 2008)
PONTIAC VIBE (2003 - 2008)
SCION XA (2004 - 2006)
SCION XB (2004 - 2006)
TOYOTA 4RUNNER (2003 - 2009)
TOYOTA CAMRY (2002 - 2006)
TOYOTA CELICA (2000 - 2005)
TOYOTA COROLLA (2003 - 2008)
TOYOTA ECHO (2000 - 2005)
TOYOTA FJ CRUISER (2007 - 2009)
TOYOTA HIGHLANDER (2001 - 2010)
TOYOTA MATRIX (2003 - 2008)
TOYOTA MR2 SPYDER (2000 - 2005)
TOYOTA PRIUS (2004 - 2009)
TOYOTA RAV4 (2001 - 2005)
TOYOTA SIENNA (2004 - 2006)
TOYOTA SOLARA (2004 - 2008)
TOYOTA TACOMA (2005 - 2014)
TOYOTA TUNDRA (2005 - 2011)
TOYOTA YARIS (2007 - 2014)

Run the car and see if check engine light goes off/stays off with their MAF or not. If not, then it's the O2 sensor (unless if ultra-rare chance it's both).
 

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Discussion Starter #19 (Edited)
Quick update:

My son ended up buying the MAF sensor anyway and not surprisingly, the P0171 code came up again. Ran this through the scanner afterwards. After reconnecting the battery terminal, we got the temporary rough gas pedal conditions again, with the P0171 code as well as codes for misfires in cylinders 1, 2 and 4. After the gas pedal issue disappeared, we reset the codes and the P0171 returned, but not the misfires. So it seems the response issues from the gas pedal are just from the engine relearning its timing patterns after a battery reconnect. Since the misfires do not come back, I'm assuming it's unlikely a tune-up is needed at present.

As for the P0171 code, some slight differences from the prior readings after the MAF replacement. Whereas previously the STFT1 readings were at -3.1% when idling and at 1.6% at 2500 RPM, they now read 14.8% at idle and 0.0% at 2500 RPM. So they are now dropping considerably instead of rising slightly. The LTFT1 readings are slightly higher than previous (now 44.5% at idle, 41.14% at 2500 RPM); however, it's still a consistent 4% drop when run the engine at 2500RPM . MAF readings are very similar to previous (between 3.0 g/s and 5.9 g/s). O2 1x1 is reading with normal fluctuations; 02 1x2 is still hovering in the lower range (around 0.1V regardless of RPMs).

Since the readings are still low for the O2 1x2 sensor, I will likely tackle that next. Safe to assume that is the post-cat sensor and that means ripping out the passenger seat and carpet to access it?

Before I do, however, in an earlier post you mentioned "if no intake or exhaust leaks, I would say 02 and poss MAF." With that in mind, should I check for vacuum leaks first, before tackling the O2 sensor, or is it unlikely a leak would cause one sensor to consistently read low? Please let me know your thoughts.

Many thanks!
 

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When I went through this, I remember buying a can of starter fluid to test for intake leaks. On a COLD car, start her up, and spray starter fluid around injectors and intake manifold. If RPMs go up when you do that, you got an intake leak. A cigarette *might* work too, seeing if the smoke sucks in or not--but I would prefer starter fluid method. As far as post cat 02, no it's easy. Disconnect Wiring from Under Seat.Take pass seat out (for access/room). Along/under center console where carpet goes up behind it, you will see the rubber gromet ,and wiring where it goes through to the oxygen sensor.


http://www.toyotanation.com/forum/26-yaris-scion-ia-vitz-echo-forum/474769-toyota-echo-oxygen-sensor-change-diy-due-po141.html

*High STFT and LTFT generally are "bad"...as it means there is excess air coming in that computer cannot compensate enough fuel for proper mixture as still to much air, and can't go any more rich since maxed out...I think? I seem to remember FT readings around 15-20 at 2k RPM or something, so something is still making it try to run richer--yeah I would check for intake leaks. There are some good videos showing how to spray it around. Take off plastic engine cover for better access to injectors. But faulty o2 can cause this by giving faulty readings, so buying cheap can of starter fluid could/would help rule out intake leaks. Use the straw supplied with the fluid to get around/in the intake->block mating area (tight/hard access..tricky).
 
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