P0171 & P0172 codes

[lit666]

P0171 = running lean in bank 1

P0172 = running rich in bank 1

pulled these off my 04' trailblazer 4.2 v6, any ideas, I replaced the fuel filter and bought some injector cleaner to maybe solve it. 84k miles.

[That_Guy]

just pull the wires off your battery and hit the brakes. then hook it back up.

i had the same thing happen on my car. i can also catch up with you and data log and clear it for you with my dash hawk. just to make sure its not a false code.

im assuming there are no mods on the car..

[theavenger333]

that big bad 4.2 is an inline 6. tisk tisk. gotta love that ^ answer though. rather than FIX a potential problem, which is what CEL codes are for, lets just clear the codes.

[That_Guy]

that big bad 4.2 is an inline 6. tisk tisk. gotta love that ^ answer though. rather than FIX a potential problem, which is what CEL codes are for, lets just clear the codes.

hence the data log.:durr i can run a data log on it to see if there actualy something wrong or if it was false reading of the first startup with no fuel pressure in the lines..

like i said i got the same reading when i changed out mine. i did a data log and found that it was just an issue from losing pressure and building it back up.


but hey.. your a great reader you must have caught all of that in my original post.

[BAD LS1]

Bad pre cat o2' will give those swings to go so far lean or rich, or a an opening in the air intake tube after the maf.

[BAD LS1]

just pull the wires off your battery and hit the brakes. then hook it back up.

i had the same thing happen on my car. i can also catch up with you and data log and clear it for you with my dash hawk. just to make sure its not a false code.

im assuming there are no mods on the car..

HUH?

[lit666]

I'll check the intake tube and maf, I haven't done anything with those for about 2k miles when I changed the air filter. Someone else said the o2 sensor on the trailblazer forums. Is there a way to test each one?

[BAD LS1]

I'll check the intake tube and maf, I haven't done anything with those for about 2k miles when I changed the air filter. Someone else said the o2 sensor on the trailblazer forums. Is there a way to test each one?

Wouldnt hurt to get a can of the MAF cleaner from an auto parts store and clean the cross hairs in it incase they have a 5 o' clock shadow on them, even from paper filters.

There is no way to physically do a test on them unless i were to use my HPT scanner that graphs o2 sensor reponse, its pretty obvious if its failing by how lazy it swings fron lean to rich. The maf, there isnt an easy way to tell unless i look at the kinda Hz its pulling down in part throttle, if its way lower than what i would see on one that is OK it is usually corrected by cleaning it. But those are the two biggies that would cause wild swings in fuel trims to set lean and rich codes.

[Mr. Brett]

Or you could just unhook the battery and pump the brakes.

[BAD LS1]

Or you could just unhook the battery and pump the brakes.

Im still waiting to hear what exactly the theory of operation is behind this logic.:goof

[BAD LS1]

hence the data log.:durr i can run a data log on it to see if there actualy something wrong or if it was false reading of the first startup with no fuel pressure in the lines..

like i said i got the same reading when i changed out mine. i did a data log and found that it was just an issue from losing pressure and building it back up.


but hey.. your a great reader you must have caught all of that in my original post.


again... HUH????

[That_Guy]

HUH?

dont huh me.... hahaha... this is what a gm tech told me after i did mine. lol...

i did a little data log and it just showed up as a false reading. idk. if this is the same deal for the trailblazer..

[That_Guy]

Im still waiting to hear what exactly the theory of operation is behind this logic.:goof

there are capacitors in the car. when you un hook the battery the car still has charge left in the capacitors. i was told that instead of waiting 30 to an hour you can hit the brakes and that will use up whats left of the charge. this will clear your trouble code. if the trouble code comes back up then you have a problem.."this is all what i was told"

[BAD LS1]

dont huh me.... hahaha... this is what a gm tech told me after i did mine. lol...

i did a little data log and it just showed up as a false reading. idk. if this is the same deal for the trailblazer..


Wow.

You do realize to set lean or rich codes, the trims need to be above +25 or below -25 3 consecutive times and spend time there to actually set a SES light right? This is the same on ANY 96-current GM vehicle. .

This fuel PSI hoopla on crank will jsut produce a longer than normal crank to start, NOT a lean code.

That clearing codes by pumping the brakes is epic though, thats almost sig material:alcoholic

[BAD LS1]

there are capacitors in the car. when you un hook the battery the car still has charge left in the capacitors. i was told that instead of waiting 30 to an hour you can hit the brakes and that will use up whats left of the charge. this will clear your trouble code. if the trouble code comes back up then you have a problem.."this is all what i was told"


You pull the PCM A and B fuses as well as the battery, wait 5. Done. The brakes arent gonna drain a capacitor in the ECM.

[That_Guy]

You pull the PCM A and B fuses as well as the battery, wait 5. Done. The brakes arent gonna drain a capacitor in the ECM.

well im glad i now know that.. i think i need to go back to the tech who told me that and slap him

[BAD LS1]

well im glad i now know that.. i think i need to go back to the tech who told me that and slap him

Yeah lube techs arent really a wealth of info. probably the same guy i watched put mud flaps on the front of the wheel wells on a brand new duramax.

[That_Guy]

Wow.

You do realize to set lean or rich codes, the trims need to be above +25 or below -25 3 consecutive times and spend time there to actually set a SES light right? This is the same on ANY 96-current GM vehicle. .

This fuel PSI hoopla on crank will jsut produce a longer than normal crank to start, NOT a lean code.

That clearing codes by pumping the brakes is epic though, thats almost sig material:alcoholic

thats the last thing i need. ive already got michelle miss quoting me about hot cousins.

[lit666]

SES light is gone. Just turned off on its own. Thanks for the suggestions.