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Can a bad bat. cause a CEL P0171

tmag

New CEG'er
Joined
Nov 7, 2007
Messages
16
Location
San Jose
So some of you may have read my long story:
http://www.contour.org/ceg-vb/showthread.php?t=23989

So the car was charging 14+ volts when running. Then it came to a point that the car wouldn't start even when jumping..... so I figured it was the bat. (thanks Br.Apple) eventhough i did get it checked before, I figured that guy did not do a complete load check. Long story short went to 3 shops (because they didn't stock the bat.) and all came up with dead bat. check. So bought a new one, dropped the bad boy in and guess what? The car's been running good (knock on wood) no CEL for a week now. But was still a bit worried. So my question can a bad battery cause a P0171 code? The car still does rev up and down on idle so I'm still worried something is not right. Thanks again for all the help!
 
In my opinion, the battery could have caused the code.
Based on my limited knowledge of automotive electronics, I would guess
that a low voltage could cause the computer to put out any type of code.
Gary J.
 
highly unlikely. a P0171 is a "system too lean" code. my bet is that you have a small vacuum leak. that would also explain the "surging" idle that your having. i think that the CEL hasnt come back on yet because when you pulled the battery that reset the PCM. it then has to relearn everything and if you had a vacuum leak then it would relearn an adjusted value to compensate for the leak assuming it could still supply enough fuel for the extra air.

that said, check for vacuum leaks
 
bump just wanted to see any if anyone else had any ideas :shrug: . Well it's running on 2 weeks now w/out CEL (still knocking on wood) and before changing the battery, when the CEL was reset it would come back with in a day or two.
 
Like striker said, the code is because the system is too lean meaning there is more AIR in the system then expected. Most of the time that means there is either AIR leaking into the intake AFTER the mass air flow sensor, or the MAF is contaminated and not reading the incoming air properly. Has nothing to do with the battery other then the fact you disconnected the power.
 
You would be amazed what voltage problems can cause in a car. Speedos go crazy, radios will turn on and off by themselves, and who knows, maybe it can even cause a lean condition. I've never seen such a thing but nobody should absolutely rule it out. I would run it and see if the code comes back. If you're concerned, hook up a scan tool that shows live data and check out the fuel trims, upper 02 readout, and MAF mass number.
 
Well almost a month now after changing the battery, so far so good (wood now has a nice grove from my knocking). Granted the car has not been driven everyday but maybe 3-4 times a week. But as I mentioned last time I cleared the code before changing the batter the CEL came back on after a day of driving. :shrug:

Mcgarvey, where can I get a scan tool that shows live data. Will this be something I have to do in the dealers?
 
Well the wood broke, today the CEL is back on. :blackeye: Will get a code reader and post the code.
 
Anything but the cheapest code readers should display live data. Don't even bother with one that doesn't.
 
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