P0171

[cherrington17]

Just threw this code while driving today. (sucks, cuz I just got my speakers back in... I guess one project solved = one project created)

What does it mean, What do I check, etc.

Got it scanned and it says "Bank 1 too lean"

That mean cylinder 1 isn't getting enough fuel, correct? Or is it most likely a bad oxygen sensor?


How do I go about diagnosing the problem, and correcting it?

[misslindseysue]

Bad O2 should throw an O2 code, not a fuel trim code. Bank 1 means either Cylinders 1,3,(5) or 2,4,(6). I don't remember how GM names them. Usually the first cylinder to get air is #1. Anyway - too lean could be an intake leak, gasket leak, injector issue, or even bad gas.

[cherrington17]

hmm.. one of the "probable causes" from the code reader was "O2 sensor defective"

so ignore that? (i'm totally unfamilar w/ codes) I suppose our sensors have their own code then?

So... run come injector cleaner?


can running lean for a while, while i try to figure this out, cause any problems?

[mfuller]

Check your fuel pressure at the rail, and then check for exhaust and/or vacuum leaks.
My car ran pig rich with a bunch of exhaust leaks (it reaked of fuel), but I still threw a lean code.
These cars cannot determine which bank is running lean since there is only 1 upstream O2 sensor (which reads both cylinder banks).

[cherrington17]

Check your fuel pressure at the rail, and then check for exhaust and/or vacuum leaks.
My car ran pig rich with a bunch of exhaust leaks (it reaked of fuel), but I still threw a lean code.
These cars cannot determine which bank is running lean since there is only 1 upstream O2 sensor (which reads both cylinder banks).


ok. how?

i've also been reading its most likely due to a dirty MAF. so.. they(they = the internetz) suggest brake cleaner to spray it with... yes? no?

[fielder87]

check your gas cap man!

[Redog]

Gas cap is a 442 code ;)

Get a vacuum gauge tester thingy, Probably have those for lending at Autozone

[bdyman]

system to lean (bank 1)

do what matt says, replace the upstream 02, clean out the maf sensor, i vagely remember but i want to say carb choke cleaner will clean out the maf
mechanics have some kind of leak detetor machine it blows white smoke so they see a leak, but anyways try that see what happens

[cherrington17]

found some carb cleaner in my garage... gave the MAF a good spray (noticed some dirt on one of the little bars) so hopefully that'll clear that up.

if that indeed was the problem.. how long till the SES light goes away?

[Cliff8928]

DTC P0171

Circuit Description

The powertrain control module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open Loop and Closed Loop. During Open Loop, the PCM determines fuel delivery based on sensor signals, without oxygen sensor (O2S) input. During Closed Loop, the PCM adds oxygen sensor inputs to calculate the short and long term fuel trim, fuel delivery adjustments. If the oxygen sensors indicate a lean condition, the fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, the fuel trim values will be below 0 percent. The short term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. The long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. If the PCM detects an excessively lean condition, diagnostic trouble code (DTC) P0171 sets.

Basically, the repair info suggests either an oxygen sensor, vacuum leak or air intake leak. Or an A.I.R. leak if you have that system on your car.

how long till the SES light goes away?

Conditions for Clearing the MIL/DTC

The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.

[cherrington17]

well.. cleaned the MAF, took it for a drive yesterday, and it kicked back on. So i guess 02 sensor is next.

where do i find the upstream one, and how hard is it to get at?

I remember there being debate about heated/non heated? which does the 3400 have?

[-Alero-]

to be honest cherry. i had a bank 1 too lean code some time ago, and it turned out my adjustable fuel pressure regulator was the culprit.

it was the one PFYC.com used to sell, i dont think they were ever good to begin with. but i ended up going back with the oem one and it hasnt come back yet

[lvemy3100]

dont do the o2 sensor yet... try to see if you can find an exhaust or intake leak as well as check the fuel pressure to ensure the FPR is working properly

after all that if the issue is still present then go ahead and try the o2 sensor

BTW- dont use carb cleaner on electronics.. they actually make MAF cleaner spray that is plastic and sensor safe

[cherrington17]

i have a bone stock AFPR. I guess I just go about replacing one thing at a time, until the light stops. :lol:

its not like you can test any of these. (O2, sensor i know you can check its operating voltage/ohmage)

dont do the o2 sensor yet... try to see if you can find an exhaust or intake leak as well as check the fuel pressure to ensure the FPR is working properly

after all that if the issue is still present then go ahead and try the o2 sensor

BTW- dont use carb cleaner on electronics.. they actually make MAF cleaner spray that is plastic and sensor safe

too late. I already hosed the MAF with carb cleaner. :glare: I can't really check for those intake/exhaust leaks myself, can i? I want to do as much as i can before taking it to a shop. i HATE paying slacker mechanics labor for doing remedial stuff i can do myself. (and most of the time, they know less about the car then i do)

[cherrington17]

just a thought... if it was my fuel system, wouldn't my car run differently? its running great. no sputtering, nothing. starts quick, runs beautifully.

makes me think intake/exhaust issue..

so vacuum hoses on the 3400... are where?

I can easily spot them on my dad's ls1, they have huge f'n hoses. But mine.. i'm not completely postive.

the Intake has one on the top. And thats the only one i'm positive about. Where are the others i should be checking?

[99alerogirl]

ps... autozone does rent a fuel pressure tester. i just used it last week :)

good luck. but with my experience P0171 is an O2 sensor.

[cherrington17]

thats what i've been told by my driveway mechanic friend. (60yr old who has been fixing cars since he was able to lift a wrench)

[-Alero-]

cherry if you get a upstream be sure to get the AC-delco ones, the NTK ones and bosch ones just dont send the same feedback as the delco ones.

Summitracing always has great prices on thier sensors, GMpartsdirect was rather fair.

both very fast shippers

[cherrington17]

is the o2 sensor 4 wire/heated??

[cherrington17]

http://contentinfo.autozone.com/znetcs/job-info/en/US/08001001.jpg/1.image

which does our car have for the upstream? i'm thinking its the one after the join from the front/back (in the pic) bank 1 sensor 2?

[-Alero-]

of course to answer first question


umm your upstream is right bnext to your coil packs its a very short one its the cheapest, as you know we only have 2.... and i believe they are all on the Bank one side cylinders 1 3 5 side.

[-Alero-]

http://www.gmpartsdirect.com/catalog/frameset.cfm
(change year accordingly)

http://store.summitracing.com/egnsearch.asp?SearchType=Make&N=700+4294924641+4294908158+4294907386+4294840048+ 115+4294859014

(apparently they dont have acdelco)

[cherrington17]

so in the pic... it would be best represented by bank 2 sensor 1?

right near the coil packs?? hmm.. so swapping it out is no problem?

[cherrington17]

http://www.gmpartsdirect.com/catalog/frameset.cfm
(change year accordingly)

http://store.summitracing.com/egnsearch.asp?SearchType=Make&N=700+4294924641+4294908158+4294907386+4294840048+ 115+4294859014

(apparently they dont have acdelco)

it looks like the local autozone might have bosch ones, in stock. and my bro gets a discount... so i'll probably go that way.


so borrow the tool, get it out, put new in, relink the wires and i'm done? is it really that easy?

[-Alero-]

errr check my links, but the only tool you need is a "sparkplug socket" every single auto parts store sells them, they are 9/10 a universal size. all you need is that socket and the drive wrench and its cake, the sensore will come with lube and everything for you.

trust me the upstream is a walk in the park, direct plug in play. Also Deep Creep spray by the same people who make Seafoam, works terrific for loosening up the bung...hole


stay away from bosch O2 sensors and spark plugs.

[cherrington17]

only need a sparkplug socket? got like.. 4 of those. :lol:

not that i don't trust your judgement, but can someone else chime in on the bosch O2 quality? I'd really prefer to just pick one up in a store, rather then order and wait... (i know the bosch s.plugs are garbage in our engines)

plus.. paying like... 50 or 60 for the plug beats the 100 for acdelco.

[-Alero-]

yeah if i recall years back someone was ranting about how they got into a mess of problems.

ive never used one im sure you can buy one and see where it takes you autozone is very forgiving and can probably take the return if you run into a problem and want to change

[cherrington17]

especially since family works there. :lol:

[-Alero-]

wont hurt, like i siad worse case scenario they will take it back and all yo usay is "it didnt work"

[Redog]

http://contentinfo.autozone.com/znetcs/job-info/en/US/08001001.jpg/1.image

which does our car have for the upstream? i'm thinking its the one after the join from the front/back (in the pic) bank 1 sensor 2?

We only have the Bank 1 Sensor 2 and Bank 1 Sensor 3 as they are labled in this pic.

You said you have a totally stock AFPR? So you have a Stock adjustable FPR? :rolleyes2:

[cherrington17]

yep. its definitely the stock adjustable. :glare: smartass...

ok.. so as per the pic (that apparently isn't close to legit) am i going to get the sensor from over the engine, or underneath?

[-Alero-]

cherry - its in plain sight it looks liek a big spark plug haning out of the top of your rear exhaust near firewall, its to the left of your EGR and in plain sight im telling you its a walk in the park to change.

[Redog]

yep. its definitely the stock adjustable. :glare: smartass...

ok.. so as per the pic (that apparently isn't close to legit) am i going to get the sensor from over the engine, or underneath?


You said it buddy :p

Yeah it's not that hard to get to if you don't have the stock air box. I can see my O2 sensor from the front on the engine (left side of the car :rolleyes2: ) and reach it pretty easy from there. If you have a stock airbox, laying on the top of the motor may be the option. Actually looking at hte pic, it looks pretty close to where it is

:lol: it will say 3400 SFI on your belly when you are done :lol:

[cherrington17]

good LORD its easy to get to! :lol:

wd40 is soaking in, hopefully it won't give me any trouble getting it out.

i also thought i was going to be cutting splicing wires. pfft.. this is cake!

[lvemy3100]

I can vouch for the fact that bosch o2 sensors are crap


Denso or AC Delco are fine (iirc the Delco's are made by denso.. could be wrong though)

[cherrington17]

well.. i have a bosch in there now. I'll give it a shot (it was the only in stock) Probably end up ordering one from rock auto, if this one doesn't drop the code

[cherrington17]

ok.

cleaned MAF, then disabled the code.
Code came back.
Replaced upstream 02, disabled the code.
Code came back.

What connectors am i checking for vacuum leaks? How do i check injectors?

[Nate's Alero]

i would run STRONG injector cleaner through it, the ride from WNY will be good for it,

and im sure someone, (like me) can have a look, i did all new injectors on my ho... and i think the old ones are alright..

[cherrington17]

this weekend i'm testing a new MAF... see if that works. I did throw some injector cleaner into it. But i've always used the same gas, from the same place... never had an issue.

[Nate's Alero]

this weekend i'm testing a new MAF... see if that works. I did throw some injector cleaner into it. But i've always used the same gas, from the same place... never had an issue.

if not, check the UIM seal, mine was bad, and i found out that both the "ears" on my LIM broke off, check that out, get some starter fluid and spray around the UIM, LIM and EVAP hoses (little green screw on cap near the main fusebox, thats the canister)

[cherrington17]

replaced my MAF, killed the code. let run for several minutes. Code didn't come back yet. I hope its dead forever.

[Nate's Alero]

awesome :)