2005 Corolla CE P0171

yeowguy

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#1
I have a 2005 Corolla CE with a trouble code P0171. The values of the MAF are.3lb/min and the O2 Sensor has a voltage of 0.055v. Is this indicating the 02 sensor is bad?
 
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#2
Did you try cleaning the MAF?....it could just be dirty....it could also be a vacuum leak...might be the intake gasket leaking...Jim
 

yeowguy

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#3
I have not cleaned the mass air flow sensor. I will try that tonight. What is the easiest way to find vacuum leaks? there are a lot of hoses to check around the car.
 

yeowguy

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#5
I sprayed the MAF sensor with MAF Sensor spray and reset the check engine light. The light turned back on
 

billr

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#6
How about the car-cleaner, looking for vacuum leaks, like Jim asked for? Are you saying the MAF always reads .3, or does it increase with engine load/rpm? Did cleaning the MAF sensor have any effect on the readings? Do the IAT/MAT readings look "reasonable"?
 

yeowguy

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#7
Which hoses am I going to be spraying? Also, it didn't appear the value changed with the engine speed. The O2 sensor readings did change however with the idle speed
 
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#8
If you just spray carb cleaner around the intake manifold where it bolts to the engine and spray the vacuum hoses where they attach you should be able to hear a change in the idle if it does have a vacuum leak...Jim
 

billr

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#9
Okay, if MAF reading doesn't change when you rev the engine up, sure seems like something is wrong in that system. Can you obsever the MAF while driving around, so that engine is under load (just for confirmation). The IAT sensor is often integral with the MAF unit, sharing an electrical connector. That's why I asked about the IAT; if it is way off, a good look at that connector is the next step... probably the next step anyway.
 

yeowguy

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#10
I will try spraying around the intake and the hoses to see. I can also check the MAF reading while driving. I will give that a shot. I'm not sure if it matters, but my computer doesn't read the voltage of the MAF. It only gives me the lb/min. Should the IAT reading be close to the MAF reading? I just did the O2 sensor a couple years ago that's why I find it so hard to believe it is bad again.
 

billr

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#11
The IAT should be close to the temp of wherever the intake air is coming from, but a bit higher because the air heats some going through the under-hood ducting. When the engine is cold, the IAT should be almost identical to the ambient air temperature on that particular day; when the engine is hot the IAT will often be more like 100-150F due to under-hood temperature. When you shut off a hot engine and it sits for a bit, the IAT may get towards 220F, but should drop down quickly after the engine is started. MAF values in #/min is fine, just get some idea of the range. If it is still stuck at .3, then we doubly-know something is wrong in the MAF system!
 

autodr

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#12
0.055? what is the downstream reading (as a second opinion to the upstream)? If you spray clean in the air filter, does the upstream o2 react?
 

yeowguy

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#13
Ok I have all the readings from he car while idling at 800RPM and then at 3,000 RPM. I was incorrect with the MAF sensor reading, it does change with an increase in RPM. Is there a way to post the readings if that helps? The MAF sensor is 0.2lb/min at 700 RPM and 1.1lb/min while at 3,038RPM. The O2 Sensor 2 Bank 1 fluctuated from .760V and .175V while idling at 800 RPM and then 0.680V while idling at 3,000 RPM. O2 Sensor Bank 1 fluctuated from 3.259V to 7.995V while idling at 800 RPM and 3.274V while idling at 3,000 RPM. The idle did not change while spraying the vacuum lines. Does this help diagnose it at all?
 

yeowguy

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#14
Correction: Ok I have all the readings from he car while idling at 800RPM and then at 3,000 RPM. I was incorrect with the MAF sensor reading, it does change with an increase in RPM. Is there a way to post the readings if that helps? The MAF sensor is 0.2lb/min at 700 RPM and 1.1lb/min while at 3,038RPM. The O2 Sensor 2 Bank 1 fluctuated from .760V and .175V while idling at 800 RPM and then 0.680V while idling at 3,000 RPM. O2 Sensor 1 Bank 1 fluctuated from 3.259V to 7.995V while idling at 800 RPM and 3.274V while idling at 3,000 RPM. The idle did not change while spraying the vacuum lines. Does this help diagnose it at all?
 

billr

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#15
That sensor 1 has me puzzled. Any readings much higher than 1V suggest that it is a wide-band. The controllers for those can output any voltage the OEM wants, of course, but I am used them being in the 0-5V range.