P0641 Loss of 5V Reference/ Fuel Trim 3 30% - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 3 (permalink) Old 10-14-2016, 01:53 PM Thread Starter
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P0641 Loss of 5V Reference/ Fuel Trim 3 30%

Hi there.. I have been struggling with the code above on my 2010 Cobalt (about 70K miles). Initially, I replaced the MAF sensor, cleared the codes, and it ran fine for 350 miles or so, and then threw the same code. All the listed diagnostic tests come back OK, or N/A (assuming this means they are not relevant). It seems to come and go, so I am now thinking it is a loose wire, or bad connection somewhere. Anyone know of a "likely" place to start? I also noticed the Fuel Trim 1 is ok, but the STFT 3 & LTFT3 were running at 30% at the time of the code trigger. Any ideas or thoughts are welcome on that as well. Thanks!!
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post #2 of 3 (permalink) Old 10-19-2016, 08:07 AM Thread Starter
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Yesterday, I pulled apart the air intake assembly to clean out the throttle body throat. In the process of putting it all back together, I found the gasket/seal underneath the air filter has sagged to the point of major intake leaking. I temporarily sealed the gaps with the dirty towels from the throttle body, and low and behold, after a few miles, the issues disappeared, and now the check engine light has turned itself off! Can anyone tell me if the air temperature being too hot (major leak pulling in air right off the engine) would throw off the MAF reference voltage.. thus giving me all this trouble?
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post #3 of 3 (permalink) Old 10-19-2016, 09:43 AM
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Yes, yes and yes, that will give you all sorts of codes but usually the first one tested, plus your engine would run terrible at idle.

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fuel trim , ltft , p0641

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