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Old 01-04-2010, 05:24 PM   #1
Kubs
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Check Engine Light Code P0174 Please Help

Driving home from work today I got a check engine light. I stopped at AutoZone so they could tell me what it was but all they could tell me was its a P0174. They didnt have a listing for what that was in a BMW but they gave me one for a VW which he said should be the same. It came on because of a "Lean Condition" caused by one of the following: Faulty O2 in Bank 2, Large Vacuum Leak, or Faulty MAF sensor. Do these sounds right for a BMW?
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Old 01-04-2010, 05:33 PM   #2
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Bank 2 (Too lean) so oxigen sensor should be looked at or replaced
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Old 01-04-2010, 05:35 PM   #3
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Yes it does. Here's one thing to try, go back to autozone, purchase CRC MAF Cleaner, remove your MAF from your car, clean it as per directions, re-install, clear the codes, see if they come back.

if they do, you could have a crack in your intake boot or a bad 02 sensor.

In before everyone else on this forums gives you useless " Search search search " talk .. i will say search around though, quite a few ( including me ) people have this problem.

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Old 01-04-2010, 11:29 PM   #4
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Yeah , check you lower intake boot, I found a crack where the idle control valve connects (vac leak)
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Old 01-05-2010, 06:33 AM   #5
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Thanks guys. I wasnt sure if the VW code list could be used on the BMW as well. The car seems to idle fine, but I will check any possibilities of a vac leak around the intake. I didnt really drive it too much but it seems to have no power and sputters under load. I will see what I can find with a foot of snow outside.
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Old 01-05-2010, 06:58 AM   #6
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Originally Posted by djnekkon View Post
Bank 2 (Too lean) so oxigen sensor should be looked at or replaced
Which one is bank 2? Autozone.com is only showing before or after catylitic converter? How many O2s are on the car?
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Old 01-05-2010, 11:43 AM   #7
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Is it bad to drive it like this? It may be a day or two before I can get it fixed.
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Old 01-05-2010, 11:52 AM   #8
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It's fine to drive it like that.

Also, any codes that start with P0___ are generic codes that are similar for all makes (though the root cause of the problem may be different); codes that start with P1___ are manufacturer-specific codes.

Surprisingly, the Autozone guy gave you good advice as to the common causes of that code.
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Old 01-05-2010, 02:45 PM   #9
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How many O2s are on the car?
There are 4: 2 pre-cats and 2 post-cats--this should be quite a dent in your wallet as it was in mine. Replacing the pre-cats are easy cheesy but the post-cats are a pita. I have to remove my reinforcement plate to get to them.
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Old 01-05-2010, 06:16 PM   #10
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I talked with a local mechanic and he said more often than not this code is produced by a slit vacuum line by the intake. I have heard by a couple people in this thread that they too had a cracked vacuum line. Does anyone have pictures of the place where this happens? How hard is it to fix? I dont know if my car will make it to work tomorrow the way it is.
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Old 01-05-2010, 06:19 PM   #11
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http://forum.e46fanatics.com/showthread.php?t=303141

take out your intake, and you will see two rubber boots.. the bottom one is the usual suspect
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Old 01-05-2010, 06:23 PM   #12
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http://forum.e46fanatics.com/showthread.php?t=303141

take out your intake, and you will see two rubber boots.. the bottom one is the usual suspect
The intake has to come off for this?
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Old 01-05-2010, 06:56 PM   #13
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Old 01-06-2010, 07:37 AM   #14
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yes
Did you mean the intake box that holds the filter or the intake manifold? I removed the box and filter and the top hose. It was late last night and dark, but I didnt see any rips in the lower boot. I will check under good light again this afternoon.
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Old 01-06-2010, 10:23 AM   #15
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The intake manifold doesn't have to come off, just the air filter box. The problem is often with the lower intake boot - the one you didn't take off. The crack is usually in the small hose on the lower boot, leading to the Idle Control Valve. The last two hose clamps are a PITA; a flexible screwdriver will help a lot. If you have a new lower boot in hand, you can just cut apart the old boot with a razor knife, which makes the process much easier.

Clean the Idle Control Valve with brake cleaner or carb cleaner while you're in there. Once you've got the lower intake boot off, the ICV is just two more bolts.



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Old 01-06-2010, 10:39 AM   #16
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Quote:
Originally Posted by geez_its_a_bmw View Post
yeah , check you lower intake boot, i found a crack where the idle control valve connects (vac leak)
+1
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Old 01-06-2010, 10:57 AM   #17
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p0174:
1. check intake boots for large or hairline tears. If torn replace..
2. check for a hairline tear on the 1/2 inch diameter tubing that runs from the top intake boot. Replace if torn..
3. Remove Adjuster unit, clean gunk off and replace, otherwise replace with new unit..
4. remove idler valve and clean (with throttle body cleaner), then replace..

If that doesn't do it, your fuel pump is on it's way out - that was the culprit in my case when I got that code. The car died on me on the middle of the road, towed it to the shop (thanks AAA), replaced the pump and the code went away.

Note: if you get the p0174 alone, the MAF is definitely okay (at least 99% of the time.) Unless you get that code in conjuction with p0171, only then you could have a dirty/failed maf sensor...

In some cases, the intake valve gaskets could be culprit but I would look there last. Also, getting lean codes imply your O2 sensors are performing as expected - when they fail, they throw a specific code..

Hope this helps someone!
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Old 01-06-2010, 11:57 AM   #18
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Originally Posted by nathancarter View Post
The intake manifold doesn't have to come off, just the air filter box. The problem is often with the lower intake boot - the one you didn't take off. The crack is usually in the small hose on the lower boot, leading to the Idle Control Valve. The last two hose clamps are a PITA; a flexible screwdriver will help a lot. If you have a new lower boot in hand, you can just cut apart the old boot with a razor knife, which makes the process much easier.

Clean the Idle Control Valve with brake cleaner or carb cleaner while you're in there. Once you've got the lower intake boot off, the ICV is just two more bolts.



Thanks! These pictures help a lot. You're right I didnt take the lower boot off and could barley see the small hose. There is a black box that is right above where the lower boot is that is not in your picture. Does that just come off with two bolts that go in the bronze looking holes?

Quote:
Originally Posted by Many330i View Post
p0174:
1. check intake boots for large or hairline tears. If torn replace..
2. check for a hairline tear on the 1/2 inch diameter tubing that runs from the top intake boot. Replace if torn..
3. Remove Adjuster unit, clean gunk off and replace, otherwise replace with new unit..
4. remove idler valve and clean (with throttle body cleaner), then replace..

If that doesn't do it, your fuel pump is on it's way out - that was the culprit in my case when I got that code. The car died on me on the middle of the road, towed it to the shop (thanks AAA), replaced the pump and the code went away.

Note: if you get the p0174 alone, the MAF is definitely okay (at least 99% of the time.) Unless you get that code in conjuction with p0171, only then you could have a dirty/failed maf sensor...

In some cases, the intake valve gaskets could be culprit but I would look there last. Also, getting lean codes imply your O2 sensors are performing as expected - when they fail, they throw a specific code..

Hope this helps someone!
This helps a lot. I will look into a fuel pump as well. How much did that cost? I am taking the car to a local mechanic who has heard of this issue on E46s before. He said he would help diagnose it for me.
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Old 01-06-2010, 11:59 AM   #19
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Also, where can I buy a lower boot if it is the issue? Is that only a dealer part?
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Old 01-06-2010, 01:42 PM   #20
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Any parts supplier should stock the lower boot, but unless you're ordering other parts at the same time, you might want to just get it from the dealer to avoid shipping time and charges. It's only about $15-20. You might replace the upper boot at the same time. You don't need to replace the plastic ring that connects the two.

The black box above the lower boot is the DISA, or Adjuster Unit. It's connected to a butterfly valve inside the intake manifold, that changes the length of the intake manifold to help optimize performance at varying RPMs. It's step 3 in Many330i's post, above. If you want extended information on the operation of the DISA, read here:
http://forums.my330i.com/showthread.php?p=55148
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