check engine light. code P0171

light came on, engines been starting and running rough...had it scanned, had the code run and now i have a list of a million different things it could be. does anyone know of any very common problems that may cause this code or anything to fix or check. the guy at the shop said this may be a very expensive and important problem so any help would be great

P0171-System too Lean

This code can be caused by many different issues. First up, what year and engine?

ya i believe its on bank two. anyway its a 97 grand prix gtp. supercharged engine.

We only reference Bank 1 since we do not have a Bank 2.

As mentioned DTC P0171 indicates the system is in a lean trim mode. Ideal fuel trim = zero. Greater than zero indicates the PCM is adding fuel to compensate for the lean condition. If fuel trim is less than zero the PCM is reducing the amount of fuel to compensate for a rich condition.

There are many possible causes for this specific DTC and it may not be easy to pinpoint the exact cause if it is not obvious and further diagnostics or parts swapping is needed. With a full function odb-ii scan tool you can check short and long term fuel trim values and that may help pinpoint the cause better.

Here are some causes.

Vacuum leak . Check all vacuum hoses at intake system. Possible supercharger or LIM gaskets.
PCV Valve
Possible throttle body blockage (clean input screen and body)
IAC (idle air controller valve)
Fuel injectors (bad lower o-ring seal)
MAF sensor
EGR valve
Bank 1, Sensor 1 02 sensor (Pre-CAT converter)

ya thats some of the things i was told it might be. i checked the air intaked and throttle body screen and most of the hoses but havent got to the rest of them seeing as i only had about an hour. i was just wondering if there was a single common problem that happend on grandprixs to cause it for example like a certain specific hose tends to leak or something. thanks tho ill be sure to check all of those things

Nope. Just one of those diagnostic trouble codes you wish you'd never get but not specific to just Grand Prixs nor is there a single common fix. All I can say is process of elimination and cross your fingers. If you could get the short and long term fuel trim values we can tell you what direction to head or narrow the possibilities down.

for about six months i had been using 87 octane gas right after i got the car, cuz no one ever told me i should run premium. do u think that might have caused damage that lead to the code

Hard to tell if running the wrong grade gasoline is the cause since you can get this particular DTC even running the proper gasoline. So we would be speculating. But I am assuming you are now running premium unleaded 91 octane or better?

Try the simple causes listed first. Start with the MAF sensor. Disconnect it and see what it does or if driveability improves or returns.

i disconnected the MAF and when i did the car wanted to stall out. the overall feel was much worse than before. as it is when its connected it hesitates and doesnt really go anywhere till about 2000 rpm. there is also a very noticeable loss of power. im going to clean the maf anyway. is there any sort of gasket or sealent on it that i should be aware of

Spray some carb spray at the base of the intake or by the vacuum lines. If the idle smooths out then you found your leak. I am dealing with the same problem.

i dont have any carb spray or parts cleaner. is there any household spray i could use? wd40 or anything?

WD-40 or similar spray lubricants will work to find vacuum leaks too, but don't spray it anywhere near the MAF sensor, as the oil in it could mess the MAF up. If no vacuum leaks are found, I would strongly suggest getting it scanned and then post the short and long fuel trim values as bnaylor suggested. That may help point you in the right direction, rather than hit and miss guessing.

short term fuel trim is at 20. long term is at 16. i believe thats maximum for both but im not sure

For short or long term values you should indicate whether it is positive or negative. But since the DTC is P0171 we are assuming it is positive and above 0%. 20% is the maximum reading but ST and LT values towards 0% is what you should see. Basically you have an excessively lean condition meaning the PCM is having to add fuel to make it richer and keep the air/fuel mixture ratio at the ideal 14.7:1.

ya thats what the guy who scanned it said, we just have no idea what the cause is. we cant find any leaky vac hoses, im assuming the MAF is ok because the car doesnt try to stall anymore, and drivability was worse with it unplugged, there are no obstructions in the air intake or throttle body. where should i go from here

How is your fuel pressure? Abnormal fuel pressure can set the DTC. The DTC can be caused by leaky supercharger or lower intake manifold gaskets. Basically, a manifold vacuum leak. You can use starter fluid spray or propane to some extent for leak detection. Check where the supercharger mates to the lower intake manifold and where the LIM mates to the cylinder heads. And then each fuel injector where they insert into the cylinder heads looking for possible bad lower fuel injector o-rings. Also, where the throttle body mates to the supercharger. I would not use carb spray cleaner because it may damage the rubber and plastic parts and wiring. Look for changes in idle. Did you have the mechanic run an engine vacuum test?

we didnt do a vac test but we could. hes my friend and we were doin as much as we can without using the shop he works at cuz they charge him to use it. but if we cant find any other causes we may have to try that.

Were those long term & short term fuel trims taken at idle? Can you get another scan at both idle & again with the boost around 0?

Best thing to do is the easy stuff or external it rule it out before going internal to the engine. On engine vacuum you can tap into the MAP sensor vacuum line or right off the throttle body vacuum lines. Range is 15 - 22 in-hg with a typical 0-30 in-hg automotive vacuum gauge. A good typical reading at idle will be around 17-19 in-hg and then take rpms to 2000 where the reading will probably be higher once it stabilizes.

Didn't you have an issue with overheating? These two issues could be related and I would suspect the supercharger and LIM gaskets especially if they are the original or never been replaced. Upon tear down and further inspection you will see they will not be in too good of shape considering you have a '97 GTP and based on your mileage. Mine looked terrible when I replaced them a few years ago when I upgraded to a S ported M90 supercharger.

well i just had it scanned again and got more codes... i know the P0171 is lean fuel and P0118 is that the coolant sensor is sensing wrong basically, and i dont really know about the P0102. for the 0118 and 0102 codes i could use some help if anyone knows anything about them or any possible remedies itd be great. thanks

well i just had it scanned again and got more codes... i know the P0171 is lean fuel and P0118 is that the coolant sensor is sensing wrong basically, and i dont really know about the P0102. for the 0118 and 0102 codes i could use some help if anyone knows anything about them or any possible remedies itd be great. thanks

TDWPgtp,

Your latest post has been merged with the existing post you had which appears to evolve around the same issue(s). Try to keep these issues together so it cuts down on confusion, duplication or redundant answers.

The P0118 DTC is related to the ECT (engine coolant temperature) sensor. A high input. The P0102 DTC is a MAF sensor issue. The PCM module has detected a low frequency input from the MAF sensor of less than 1500 Hz.

im sorry i thought it was an unrelated problem and that the code just hadnt been reset. but im assuming it is because of this because i had the code cleared and it did come back again. they supposedly cleaned the injecters and replaced the upper and lower manifold gaskets as well as the super charger gasket. no vac leak has been found and i would assume that they checked the MAF but im not sure as of now i didnt get to talk to the guy yet. ill be stopping by either tomorow or wednesday and will post here with more info
thanks

Check for vacuum leak. The tube from my intake boot to the intake manifold was off. Car runs smoother and P0171 went away.

Four year old post.....hope TDWPgtp sees this....