Found cause of P0172 & P0175 DTC's

[Bill K]

Originally Posted by Harley Monster

M5James...I have a question on the O2 sensors.

These are original (118,000), is it best to change them out before failure or is it best to wait until they do?

My dad used to say, "If it aint broke, don't fix it..."

Will the failure of the O2 sensors leave you stranded? Or does it start out with an SES light?

I guess it is OK to hijack my own thread.

Change the front two. They are the most important ones. I just did and they are very easy with the proper tool. The wiring connector is under the plastic head cover. Once you replace those front two, you will be pleasantly surprised at the extra power your car puts out. It made a real difference. Also think about the spark plugs if they are old. As for parts, look online, the O2 sensors can be had for about $65 each.

[Harley Monster]

Thanks for the advice BillK...

I do have the tool and knowhow to replace the O2 sensors as I have been involved with mechanical things my entire life. My problem is I am now retired and have taken the same hit as everyone else so I do not like spending money where it is not necessary.

I did replace the sparkplugs at 60,000 miles (rec. 100,000) on the advice of an Indy mechanic and I picked up 2 MPG when I did...that was good advice. On that schedule, they are due again. I can see now I could gain a similar effect by changing the O2 sensors, I had not considered that before. Thanks for the good advice.

Question on the Rear O2 Sensors: It is my understanding that the Rear O2 Sensors do not send a signal to the DME for tuning and they are only there to signal a mass failure in emission control; therefore, they do not affect performance. If this is true it makes sense to leave them alone until they fail and trip a DTC and throw a SES light.

Is that a true statement?

[m5james]

Exactly right. The post car 02's are there to simply make sure that you've got functioning catalytic converters, they don't actually do anything tuning wise and only send a CEL when they sense something is wrong with your emissions.

[Harley Monster]

Thanks M5James...

Do you also agree that early replacement of the Pre-Cat O2 sensors is a economically wise move?

[m5james]

It was my suggestion in post #14 to replace them around the 80-100k mark, so you'll more than likely see the same benefit you did at 60k when replacing the sparkplugs. I'm more of a proactive than reactive mechanic, but that's just me.

[Harley Monster]

Thanks M5James...

Coming from an aviation background I am big on preventative maintenance too.

Thanks for your advice and time, it is appreciated.

[m5james]

Small world, as am I...but I'm sure you've been doing it for longer. I'm a former F14 Plane Captain/Avaition Structural Mechanic, then worked for Boeing/Lockheed Martin on the F22 as a Special Projects Mechanic in both Seattle and Atlanta area. I'm currently looking at temporarily moving to where Boeing may take me as I've applied for about 6 jobs there, anywhere from Seattle to St. Louis to Qatar.

My grandfather used to built, fly and even had a company making throttle quadrants for various types of bi-planes and practically everything else that could have used his services. Both uncles were military, one is a retired air traffic controller...been around aviation since I was a kid. Working on cars is just "fun" for me.

[Harley Monster]

Today I tackled a the job I was not looking forward to, the replacement of the Y duct.

It is not a hard job, but it is NO FUN. The problem is getting access to the clamps, they are very tight to the engine and there is very little room to get your hands in there from above or below.

I had been told don't even try loosening the clamps with a slotted screw driver so I didn't try that, it would have been very difficult.

I tried an 8 mm socket with a small ratchet from both above and below and I just could not either get the socket on the clamp or keep it on the clamp. I fought it for about a half hour.

I finally decided a nut driver would be the best tool because it is in a straight line. I only had an SAE set and though it was working it was occassionally slipping. I then used a nut driver handle out of my 1/4" drive set with a 8 mm socket on the end of it and that worked like a charm. I did some of the work from above and some from below. The problem is when the clamp is loosened and you put pressure on the nut driver to keep it on the clamp the clamp turns out of range. I found that if I just kept the most minimal pressure on the nut driver the clamp did not turn and then I had success.

I was worried about putting the clamps back on, but using what I had learned taking the clamps off the job went very fast.

I spent 2 hours on it, 1/2 hour taking all the ducting out and then figuring out how to do it. About an 45 minutes actually working on it and the balance cleaning in areas not normally accessable.

I did clean the Throttle Valve and Idle Speed Control with some Carb & Throttle Body Cleaner, but they were not very dirty.

On one of the product reviews I read of the Y duct someone said they did it in 20 minutes. I could do that now, but not before this education.

BTW, my forarms are all chewed up from the close quarters, but once again I have kept the X5 away from the Dealer.

The first photo shows the old torn Y tube that Y's between the Throttle Valve and the Idle Speed Control. (I am attempting to point at it)

The second photo shows the Throttle Valve and the Idle Speed Control with the Y duct removed.

The third photo shows the job complete.

The X5 fired right up, idled perfectly and drove great.

I hope this helps someone.

[m5james]

Based on your pics, the inlet of both the TB and ICV look like they're on the same plane. On the 330xi I did a few weeks ago, that ICV was definately buried further back, but that's where I was able to get the hoseclamp loose via using an extra long screw driver while using what little bit of my fingers I could get in there to stop the clamp from spinning during removal/reinstallation.

Give it a 100 miles or so the ECU to adjust and it'll be running like a top all over again. You get the 02's ordered up yet?

[pdabbs911]

Thanks to all who have contributed to this thread. I just bought an x5 3.0i last week and plane to tackle this job this Friday. The write up and pics will definately help. Thanks again for the pics. I do have a couple of questions for guys: what parts need to be removed for access and how many total clamps are there? I will likely read this thread severl times before Friday just to study it. Thanks inadvance for the response.