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DIY: Do It Yourself
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Old 10-21-2019, 04:42 PM   #1
Slimtee925
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Join Date: Oct 2019
Location: Orange County, CA
Posts: 1
My Ride: Stock '05 325i
Year: 2005
Model: 325i
Transmission: Auto
DIY P0171 & P0174 Code Diagnose/Fix - Smoke Test

I’ve got a 2005 325i with 112k miles that I bought earlier this summer. SES light came on recently and I plugged in my obd2 reader and found it threw the infamous P0171 and P0174 fault codes (system too lean banks 1 and 2).

I have an obd2 scanner that gives freeze frame and live data, and found that I really only ran lean off of a cold start (Short term + long term fuel trim levels are combined over 20% for longer than 60 sec). I’m assuming it’s a small leak that gets “plugged” as the engine heats up and parts expand.


To avoid blindly changing parts and inspecting every single thing, I decided to perform a smoke test - basically fill the intake up with smoke and wait for it to leak out from somewhere. Instead of buying a $$ smoke machine, I used a 3” pvc pipe cap and screwed a nipple into it where I attached a smoke gun used for food/cocktails. I also used a good ole’ cigar and lung power at times to blow with some pressure. I tried attaching it to the air intake hose at first, but realized i needed to wedge the throttle blade open. So I removed the intake hose, wedged open the throttle blad with a random tool and attached the smoke device to the elbow piece that attaches to the TB.



While pumping smoke into the intake, I found a leak coming from where DISA valve attaches to the intake. (Ie: I saw smoke coming out of this area).

So i removed the 2 torx screws and notice that the valve just slides out without any resistance - which indicates to me the o-ring is no longer doing it’s job and providing a proper seal.

I know the seal on this DISA is a “non-serviceable” part and I should buy a complete DISA, but the valve itself is in good shape, and I’ve seen a few people on on the forums scrape out the old piece and just slide a new o-ring over it. I looked all over town and couldn’t find anything that would fit, so had to order online. I ordered a Viton Size -136 o-ring from Amazon, a pack of 10 for $4 with free 2-day shipping.

I didn’t want to put the DISA back on without attempting a fix, but the o-ring is a few days out, and this is my DD. So.... I just cut a thin slice of electrical tape and wrapped 1 layer over the existing o-ring, and it seemed to fit much better when I put it back together.

Been driving it for a couple of days and have been monitoring the live data, which is showing much better numbers on both LT and ST trim levels. SES is still on, but I haven’t driven too much yet. Once I replace the o-ring, I will reset the light and see if it comes back!

This is my first DIY write-up, so all feedback is much appreciated! Thanks!!_a_
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disa o-rings, diy, smoke test, system too lean, vacuum leak

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