P0171 on 2002 Echo - Toyota Nation Forum : Toyota Car and Truck Forums
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post #1 of 43 Old 06-07-2017, 10:33 PM Thread Starter
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P0171 on 2002 Echo

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 #

Last edited by Mumford67; 06-08-2017 at 07:53 AM.
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post #2 of 43 Old 06-08-2017, 12:48 AM
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Are you sure the code is right? I don't see that code in my info and the MAF codes show up as a P0101 & P0100?
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post #3 of 43 Old 06-08-2017, 07:55 AM Thread Starter
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Originally Posted by puddleglum2 View Post
Are you sure the code is right? I don't see that code in my info and the MAF codes show up as a P0101 & P0100?
Sorry...looks like I had a covfefe moment there. Correct code is P0171. Post above has been fixed.
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post #4 of 43 Old 06-08-2017, 08:30 AM
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That is a lean burn code, could be a lot of things, not just MAF. Search the code. I'll comment more later.
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post #5 of 43 Old 06-08-2017, 10:28 PM Thread Starter
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Originally Posted by puddleglum2 View Post
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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post #6 of 43 Old 06-08-2017, 11:11 PM
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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/2...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.

Last edited by HATEnFATE; 09-13-2018 at 12:38 PM. Reason: direct link to Toyota manual
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post #7 of 43 Old 06-11-2017, 11:33 AM
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could be MAF, and/or oxygen sensors.

Regarding the MAF:

Did you make sure to clean the inside tube portion of the sensor as well? http://www.lastgreatroadtrip.com/wp-...008/12/MAF.jpg
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post #8 of 43 Old 06-13-2017, 08:16 PM Thread Starter
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Originally Posted by l33ch View Post
could be MAF, and/or oxygen sensors.

Regarding the MAF:

Did you make sure to clean the inside tube portion of the sensor as well? http://www.lastgreatroadtrip.com/wp-...008/12/MAF.jpg
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.
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post #9 of 43 Old 06-13-2017, 08:21 PM
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cool. When you get it, look at the fuel trim (long and short) readings. Will possibly help narrow down which part(s) are the culprit.

https://www.toyotanation.com/forum/26...171-p0420.html may help.

Last edited by l33ch; 06-13-2017 at 08:25 PM.
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post #10 of 43 Old 06-13-2017, 08:42 PM
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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.

Last edited by puddleglum2; 06-13-2017 at 08:46 PM.
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post #11 of 43 Old 06-22-2017, 09:37 PM
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Quote:
Originally Posted by Mumford67 View Post
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.
Quote:
Originally Posted by puddleglum2 View Post
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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post #12 of 43 Old 06-22-2017, 10:03 PM Thread Starter
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Quote:
Originally Posted by l33ch View Post
@Mumford67

Hey, just wondering if there was any update?
Not yet. Still waiting on delivery of the Bluetooth OBD monitor. That's what you get for trying to save a few bucks by ordering from overseas.
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post #13 of 43 Old 08-22-2017, 08:38 PM Thread Starter
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Originally Posted by l33ch View Post
@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?
Attached Images
File Type: jpg Echo stats - idle vs 2600.jpg (657.4 KB, 9 views)
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post #14 of 43 Old 08-22-2017, 09:00 PM
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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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post #15 of 43 Old 08-22-2017, 09:13 PM Thread Starter
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Originally Posted by l33ch View Post
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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