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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 06-14-2012, 09:00 AM
VT.330xi VT.330xi is offline
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Po171& po174!

Hello folks, I am new to this so bare with me. Yesterday at noon, car started running rough, ran fine in the morning. Scan tool came with PO171, PO174, too lean in bank 1and bank 2. Any idea's on this would be great. Thank you!
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  #2  
Old 06-14-2012, 09:26 AM
pconwell pconwell is offline
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First, it's P(zero)174, not P(oh)174.

I'm having the exact opposite problem, running rich in banks 1 & 2. Running lean means that either you are not getting enough fuel (fuel delivery problem) or you are getting too much air (air delivery problem).


Here are some basic, simple cheap things to check first:

* Check/replace your air filter
* Clean the MAF sensor
* Check/replace spark plugs (probably not the problem, but they are easy to check/replace)
* Run some 'fuel injector cleaner' through the car. (I've used sea foam and lucas before - they both seem pretty good).

Some less easy, less cheap things to look at:
* Replace the MAF sensor
* Replace fuel filter
* Replace fuel pump
* Clean/replace fuel injectors
* Replace oxygen sensors

So, that's just off the top of my head. Someone smarter than me can probably give you some better advice, but you can at least have a general idea where to start looking now.
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  #3  
Old 06-14-2012, 10:49 AM
9benua 9benua is offline
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Beside the engine check light turn on, What's the effect of ignoring this problem? My P0171 & P0174 triggers the engine light in my car every 3-4 weeks. Car is running fine, mpg still good, no rough idle.
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  #4  
Old 06-14-2012, 10:57 AM
pconwell pconwell is offline
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Quote:
Originally Posted by 9benua View Post
Beside the engine check light turn on, What's the effect of ignoring this problem? My P0171 & P0174 triggers the engine light in my car every 3-4 weeks. Car is running fine, mpg still good, no rough idle.
I'm not sure that I am qualified to answer that. My 'gut' response is that if it's not causing issues, you should be fine.
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Old 06-14-2012, 11:09 AM
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P_T P_T is offline
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Those codes are generally associated with a crack in you intake elbow between the MAF and the throttle body. Check for leaks first before you waste a lot of time and money chasing nebulous nonreated issues.
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  #6  
Old 06-14-2012, 01:49 PM
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rgk330i rgk330i is offline
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The over lean condition is often caused by a vacuum leak (or more than one!), though a fuel delivery problem or a bad MAF sensor is possible too. The opportunities for a vacuum leak on the E46 are just about too numerous to mention. Prime candidates include the intake boots mentioned by P_T, the crankcase ventilation (oil separator) valve and associated hoses, the gasket where the DISA valve mounts to the intake manifold, the vacuum line that runs around the back of the engine and along the exhaust side of the valve cover, or even the simple little vacuum plug on the very back of the intake manifold against the firewall. I'm sure there are others too; those are just the ones I've had to deal with.

A shop will find them by injecting smoke into the intake system while the engine is stopped, and looking for where it leaks out. I find them by running the engine at idle and monitoring the short term fuel trim with an OBD-II reader while running a propane torch (unlit!) around the intake manifold and hoses looking for a sudden drop in the fuel trim.
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  #7  
Old 06-14-2012, 02:28 PM
VT.330xi VT.330xi is offline
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Cleaned MAF& air filter, checked intake hose between MAF and throttlebody, reset computer and still came up with p0171& p0174.
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Old 06-14-2012, 06:01 PM
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mlukas161 mlukas161 is offline
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I had these codes when my DISA flap was broken. Did you pull the DISA to check it yet?
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Old 06-14-2012, 07:16 PM
GLOK1132 GLOK1132 is offline
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Could also be DISA flap or the seal is bad on the DISA. I have also heard that a Fuel pump going on it way out could also cause it, but don't quote me on that.
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Old 06-14-2012, 07:49 PM
Bwood1 Bwood1 is offline
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I just had my 2001 325i in the shop and they diagnosed lean fuel trim (only under load). Said it was either the fuel filter or fuel pump. I had replaced the fuel filter about 13 months ago, but this is my daughters car and she runs it down to empty on a regular basis so we replaced the fuel filter and that has fixed it. No more SES light
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  #11  
Old 06-14-2012, 08:30 PM
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rgk330i rgk330i is offline
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It makes sense that lean under load is likely to be fuel delivery, while lean at idle is likely to be an air leak - at higher rpm, any air leak is going to be a much smaller proportion of the total air intake.
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  #12  
Old 06-14-2012, 09:39 PM
pconwell pconwell is offline
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Here is a cool DIY vacuum leak tester if you feel like it might be a vacuum leak: http://forum.e46fanatics.com/showthread.php?t=445181
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  #13  
Old 06-15-2012, 08:39 AM
VT.330xi VT.330xi is offline
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Just pulled Disa, it"s broken, pin fell out in my hand. Thanks every one for your help, hope this fixes it. Thank you for informing me of this, before I shot that pin thru my engine!
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  #14  
Old 12-26-2013, 09:17 PM
norcal325i norcal325i is offline
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When getting the 171 and or 174 codes I get a rough idle and or stalling when shifting from park to drive or reverse. I can clear the code and everything is perfect for a period of time. Then the light goes on again, rough idle. MAF is new, no visible cracks in boot... Next step DISA? Or smoke test?
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  #15  
Old 12-27-2013, 01:11 AM
SamxK SamxK is offline
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I had the exact same codes for a year. I examined my intake boots and DISA everything was okay. Changing the CCV did it for me. There was a torn oil line that was BARELY, and I mean barely visible after I had taken out my air filter and pushed all the wires and hoses aside. Check for any oil leaks around that area and around the engine cover. A small oil leak is enough to trigger that lean code (vacuum leak). Just my input for your problem. Hope it helps.
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  #16  
Old 12-27-2013, 05:44 AM
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ahull ahull is online now
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The wiki has a good link for lean code troubleshooting: http://www.bimmerfest.com/forums/sho....php?p=8014505

You have an air leak or fuel pressure issue. Read the link on these codes. It's a good guide.
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