engine light/trouble codes

**Jakegday** · 12-03-2008

hello, my "service engine soon" light came on so i took my car to autozone and got the codes. the code is p0171 and they said its in there twice.

on the piece of paper they gave me, for the first one all it says is "the pcm has determined that during testing, the fuel system for bank 1 was too lean. (bank 1 identifies the location of cylinder #1 while bank 2 identifies the cylinders on the opposite bank)

for the second one it says

Definition: fuel trim bank one condition
Explanation: the pcm uses the oxygen sensor to calculate the air/fuel ratio of the engine. the computer has recognized a rich or lean condition on one engine bank only
Probable Causes:
1. if bank 1 and 2 codes set together suspect fuel pressure or MAF sensor
2. oxygen sensor defective
3. ignition misfire-repair
4. fuel injector problem

if anyone has any ideas on how to fix this, or any advice, it would be greatly appreciated, thanks

**SyntheticShield** · 12-03-2008

Well as the list says, it could be a bad O2 sensor, but you do have to do some checking and make sure that there is no underlying cause to the lean condition. That is to say is the O2 sensor just reading incorrectly (therefore defective) or is it reading correctly (therefore not defective, just reporting that it sees the A/F as lean due to some other cause).

Unless you have a misfire code stored, which it does not appear that you do, or if you have seen your check engine light flashing which I suspect is not the case you may and I stress may possibly rule out a misfire condition. That leaves air flow or fuel flow issues.

If its either one you are going to notice a reduction in power. Now, that said, it may be helpful to post up year, make and model and what if any maintenance has been done recently, how many miles, etc.

A couple of things you can check right away would be:

1. The MAF sensor. Maybe get some electronics cleaner and clean it good and the connector. Do this particularly so if you run any kind of oiled air filter.

2. Check for vacuum leaks.

If those are all good and dont clear the issue, then perhaps replace the O2 sensor and see if that corrects the issue, or you can start there first if you like, but I like looking at the really simple things that are easy to take care of first when possible.

**Bio248** · 12-03-2008

there is no second bank on these cars, there is only one o2 sensor.

**Jakegday** · 12-03-2008

well its a 2001 grand prix GT, that i have done NO maintenence to, i just bought the car less then a month ago. it does not show any signs of a misfire condition.

im going to go to the parts store and get some MAF cleaner and spray that off. once the problem is fixed will the light go off in time or does it HAVE to get reset? and if so can disconnecting the battery reset it??

also, where EXACTLY is this oxygen sensor?

TDCRacing · 12-03-2008

x2 on checking for the vacume leaks.

**Bio248** · 12-03-2008

the o2 sensor is on the rear exhaust manifold right in the middle. if you lean over your engine you should be able to find it.

**Jakegday** · 12-04-2008

is there anyway i can reset this light myself? i read on here somewhere that unplugging the pcm/ecm fuse for 30 minutes will do it, but it didnt work for me......

TDCRacing · 12-04-2008

well i always do it with my tuner. I guess i'm spoiled. But i belive you can acomplish the same thing by unplugging the battery.

**Jakegday** · 12-05-2008

Originally Posted by Bio248

there is no second bank on these cars, there is only one o2 sensor.

i went to autozone and they said there are 2 available for this car. 1 for before the cat and 1 for after the cat. im assuming the one i need from them is the one before the cat, right????

since you said these cars only have 1 and they said they have 2, i just want to make sure i buy the right thing.....

**SyntheticShield** · 12-05-2008

There are 2 O2 sensors, but its the first one, before the cat that is the critical one as it is used in determining fueling and such. The one after the cat just mainly checks catalytic converter function.

As far as I know they are identical sensors so they should interchange but you would need to replace the one before the cat.

TDCRacing · 12-05-2008

Right....You had me curiouse so i looked Scotty, There is a different part number listed for the front and rear in a delphi sensor. Although i'm not sure anyone could actually confirm that their IS indeed a diference.

**Jakegday** · 12-05-2008

thanks for the quick reply, i cant tell you if they're the same or not, but they dont cost the same

also, how should i go about getting this out?? what size wrench do i need? i saw a socket obviously wont work.....

**Jakegday** · 12-25-2008

in regards to the vacuum leaks, i took the grey plastic cover off the top of the engine and tried listening but could not find anything. since i dont know exactly where all the vacuum lines run, i was wondering if someone could tell me where exactly i should be listening?

**Jakegday** · 12-29-2008

Originally Posted by Jakegday

in regards to the vacuum leaks, i took the grey plastic cover off the top of the engine and tried listening but could not find anything. since i dont know exactly where all the vacuum lines run, i was wondering if someone could tell me where exactly i should be listening?

anyone??

**Bio248** · 12-29-2008

you cant really hear a vacuum leak because normally they are very small. youre going to need some type of carb spray or the like and spray it all over the top end of the engine. if it revs up or bogs, youve found your vacuum leak.

**cn1151** · 01-02-2009

If your still having trouble read my post I hate P0171 code http://www.grandprixforums.net/f95/l...highlight=LTft

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