P0174 & P0171
Hello everyone,
I've done some searches around the forum and for BMW cars in general for what these two codes could mean, and there are a lot of things that can cause these codes, and I'd like to fix whatever is causing the issue without replacing every single component listed. So I figured I would explain the situations in which it comes up, to see if anyone has some insight on how to narrow down the actual cause. The codes come up very infrequently, however it is always in the same kind of situations, if I commute longer distances, 75+ miles in one drive, it will come up at the end of the next drive normally. My most recent time encountering was over a 300-mile drive and it showed up after a 10-mile drive the next day. To clarify, the engine is the 3.0. I don't really see much of a performance change, however, I know running lean can make the engine run hot, and that's a situation no one wants. If any of this was helpful to the diagnosis, let me know what you think, or if you have any other questions that could indicate the issue, please feel free to ask. P.S. I've already inspected the intake boot and intake system and haven't found any damage or leaks, except for the accordion that goes between the ram air scoop and the intake box, but it is a very small hole. |
What scanner did you use to read the codes?
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I used a generic iPhone compatible Bluetooth OBD scanner, but this same code comes up when I use PAsoft so it should be correct.
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P0171 & P0174 codes; a bane to many BMW owners
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Since the P0171 & P0174 codes (and the corresponding SES/CEL) were being triggered by extremely high fuel trim numbers, I installed a cheap $23 MAF sensor (suggested by X5chemist, which has kept the fuel trims lower, and I don't have the lean codes anymore.https://xoutpost.com/1220730-post15097.html My original Siemens/VDO oem MAF sensor must've been under-reporting airflow (despite several tries with MAF cleaner), because the fuel trims immediately dropped into a more normal range, and have stayed low for 6+ months, so far (X5chemist is still using his cheap MAF, for over a year). Concerning the small leak in "the accordion that goes between the ram air scoop and the intake box", are you referring to this tube? Attachment 82811 air intake boot Mine doesn't seal very well (another cheap Amazon replacement), but since it is placed before the MAF sensor measures airflow, then it can't be the problem. The cheap MAF may just be covering up for a yet-undiscovered underlying problem causing the lean codes, but until I find them, I'm happy to be (semi) code free. It passed emissions inspection last month! |
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How confident are you that this new sensor isn't just less accurate than the OEM ones? It seems strange that the sensor would just read badly, but maybe I just don't understand the way a MAF functions internally that would make it deteriorate. But given it's a cheap solution I'll likely give it a try. (because if that's not the issue, replacing it wouldn't fix the code??) And I don't know what you mean by extremely high trim values, according to my OBD app's readouts, my long term trim maxed at 11.96% and short term maxed at 15.2%, and I don't know what percentage actually triggers the code. Would you define those values as very high, or just marginally high? Thanks for the reply, I'll be sure to go read the thread you linked to see if theres any other relevant information to glean from it! |
stuck in the middle of the problem, with no 100% cure in sight
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A fellow forum member promised to send me a "tested good" Siemens MAF for testing, but never did. As it stands now, I'm using the cheap MAF until
From what I've read on many sites, the total of short-term and long-term fuel trims will trigger a SES/CEL when the total exceeds +/- 25%. Your example of (+11.96%) added to (+15.2%)=(+27.16%), which will trigger the SES/CEL. Presently, on my last drive, my long-term trims are about (+3.16) each, give or take, but they are being cancelled out by negative(-) short-term numbers, tending towards a total of zero. Since my long-term trims never seem to get to zero (my '04 Chevy 2500HD 6.0L has rock-steady long-term readings of zero) I must assume that
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