Thread: P0174 & P0171
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Old 11-22-2022, 08:11 PM
lkv0315 lkv0315 is offline
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Quote:
Originally Posted by workingonit View Post
I fought the same codes for 7 months (along with random misfire/low fuel pressure codes) constantly checking for vacuum leaks (none found) or a fuel pressure loss (none found), in vain.https://xoutpost.com/bmw-sav-forums/...-codes-me.html Though the codes showed misfires and/or low fuel pressure, I never felt any stumbling nor ever had hard-starting problems. I replaced the oil filler cap & seal (didn't help with the codes, but my beauty cover stays clean now), and the exhaust cam position sensor during that period (P0365 came up, so I replaced that sensor immediately), and then was at an impasse, wondering what to try next.

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!
Yes, that is the intake boot I was talking about, and I genuinely figured exactly what you said, since the trim would be calculated using MAF data.

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!
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