High LTFT but No CEL

[camrydriver111]

My LTFTs are 12% for bank 1 and 13% for bank 2. However I have no CEL. This is in a 2005 325i.

I think I know what the problem is, and it's a torn intake boot that I plan on fixing soon.

There is a "pending code" P0174 for bank 2, but no CEL, and no code for bank 1.

What I am really curious about is why these high LTFTs haven't caused a CEL?

 

[irad]

CEL is triggered at 25%

 

[Trav]

As the other poster said its not high enough for a CEL. The torn boot is the cause of pending P0174 and high LTFT.
Fix it sooner than later it is letting unfiltered air in the engine.

 

[The Critic]

My understanding is that stft/ltft values from a generic obd2 dataset are not very useful on most euro makes. You really need the BMW specific data set. BMW generally reports 3 pieces of data for fuel correction - multiplicative, additive and lambda/integrator. Without all 3 pieces of information, you may not be getting a full picture of what's going on.

 

[Trav]

That may all be true but I wouldn't overthink this. He has a known issue that can cause all the things he describes. Generic OBD2 fuel trims are useful enough.
One of the first things I learned was to fix what you know is broken first (if it is possibly related as in this case) then go from there.

 

[camrydriver111]

Originally Posted By: irad
CEL is triggered at 25%


I see. Never knew it gets triggered at 25%.

 

[bowlofturtle]

Originally Posted By: camrydriver111
Originally Posted By: irad
CEL is triggered at 25%


I see. Never knew it gets triggered at 25%.


I would of guessed 15% or 25% myself. 25% after i think about it makes a lot more sense, 10-15% would cause way too many CEL.

 

[jkasch]

My '04 GTO was getting a CEL at -17%. The tuner (a calibration engineer at Cosworth for eleven years and now Magunson's chief calibration engineer) said, "Adaptive Logic can handle 20%."

 

[Vikas]

When you look at the trim; always add (algebraically) LT and FT in your head first and then if it is over (20 or) 25% you are close to getting the CEL. Because that is what the computer is doing behind your back.

 

[Trav]

Originally Posted By: jkasch
My '04 GTO was getting a CEL at -17%. The tuner (a calibration engineer at Cosworth for eleven years and now Magunson's chief calibration engineer) said, "Adaptive Logic can handle 20%."


I have heard everything from 16% to 25% before illuminating the CEL depending the make and country, not sure if there is any sort of mandated not more than/less than number for OBD.