fault code...p0174

[Scorpius]

welp...165,700k miles and finally my first fault code. Check engine soon light came on this morning on drive to work. i have noticed this week that when i first started the car it ran but then seemed to very briefly change its normal hum and stumble very very briefly then go back to humming as normal.

throw the reader on it and it comes up with
P0174 - Fuel Trim, Bank2 System too Lean

Any ideas what exactly this code is referring to? what can i check?

[danewilson77]

Mist likely you have air flow that isn't being read by MAF sensor causing a lean condition = intake leak.

Clean MAF sensor as well.

What intake do you have?

HTC Thunderbolt+TT

[kayger12]

Pre-cat O2 sensor is a good place to start when you only get one bank. Others will chime in on this.

If you also got the P0171 I'd say intake/vacuum leak.

Moving this over to Mechanical/Troubleshooting.

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[danewilson77]

Pre-cat O2 sensor is a good place to start when you only get one bank. Others will chime in on this.

If you also got the P0171 I'd say intake/vacuum leak.

Moving this over to Mechanical/Troubleshooting.

Droid X. Tapatalk. Use it.

Yup. KG is correct.

HTC Thunderbolt+TT

[Scorpius]

Yup. KG is correct.

HTC Thunderbolt+TT

I've seen the MAF and the vaccum leaks referred to when combo of the 0171 and 0174 codes, i seriously doubt it's either considering within the last 5-10k miles (2 months) i've replaced just about the entire intake system hoses when i did the CCV, then just did the OFH and the VC gaskets which while i had the intake off (gruppem) i noticed small edges of pinestraw stuck around the edges inside the MAF so i used magnifyer and a needle to carefully clean those out from the wire where it's inbedded in the plastic. then cleaned it very well with MAF cleaner, that was about 5k ago so no codes till now.
is there any way to confirm the precat o2? resistance test or something?
Figured they were about to go sometime before 200k lol...guess i'm doing all 4 if i'm doing even just 1. ugh...what $600.00 parts.

[kayger12]

Not sure of a test for the pre-cats, but considering that their life expectancy is 60-100k, yours are most likely not doing their job well even if they're not completely shot. I'd be replacing them either way.

Not sure if it's necessary to do the post-cats as it's my understanding they have no impact on engine function.

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[Scorpius]

Not sure of a test for the pre-cats, but considering that their life expectancy is 60-100k, yours are most likely not doing their job well even if they're not completely shot. I'd be replacing them either way.

Not sure if it's necessary to do the post-cats as it's my understanding they have no impact on engine function.

Droid X. Tapatalk. Use it.

as i've been told, they are used to remeasure the precats adjustments to A/F mix and fine tune based on the reading.

[kayger12]

as i've been told, they are used to remeasure the precats adjustments to A/F mix and fine tune based on the reading.

Ahh. Didn't know that. Good info.

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[Scorpius]

well crap. got home today to look at it more (200 miles later lol) and find it threw a 2nd code as well. the p0171 if i recall. i just pulled out my MAF and found just a few little pieces of what look like leaves in some areas of the wire, took the air compressor, blew it all out. was out of maf cleaner so used starting fluid to clean it, then cleaned that off with air again, put back together, reset light....now the waiting game.
i did play around with my reader though...looks like i can monitor all sorts of cool things including the o2 sensors high/low readings (like test 81, 82, 83, 84 when i scrolled) and then voltage...shrug...they all martian to me. anyone a bmw mech and know what to look for maybe explain it to us?

[kayger12]

With the P0171 I'd start looking for an intake/vacuum leak with the lower boot being the prime suspect.