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Old 12-06-2019, 07:21 AM   #1
bluetech
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P0174

Hey guys looking for some advise were to start. I got the other day my check engine light to come on. When I pulled the code I got P0174 lean bank 2. I did reset it once and after about almost 200 miles the light came back on. Both times the light came on while driving on the highway. When the light did come on I didn't notice any difference with the cars performance. Gas mileage seemed the same. I am going to look for the obvious things like a vacuum leak (torn intake elbow which was a cause previous). But that time I had lean bank 1 and 2. If anybody is wondering the fuel pump was replaced just last March and has less than 8000 miles on it.

I did pull the freeze frame off my reader and kind of confused me between bank 1 readings and bank 2 and that is why I am asking if somebody could look at it and see if it doesn't point to a vacuum leak. Maybe to something else like a MASS air flow sensor. As it is still original with over 250,000 miles on it.

Freeze Frame
FUEL SYS 1 CL
FUEL SYS 2 CL
CALC LOAD % 60.78
ECT 94c
STFT B1 -4.69
LTFT B1 8.59
STFT B2 10.94
LTFT B2 11.72
ENGINE RPM 2089
VEH SPEED 96KMH
SPARK ADV 15.00
IAT 3c
MAF g/s 35.86
TPS 29.80%
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Old 12-06-2019, 08:40 AM   #2
CylonRed
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Various seals can cause the 174 which is a vacuum leak. Dipstick seal, seal around the DISA, brake booster can cause vacuum issues, the F-tube on the intake, among other things. Do a smoke test to see if you can find a leak... Probably pretty small if performance is not changed.
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Old 12-06-2019, 10:13 AM   #3
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Smoke Test for PO171 / 174 codes is ABSOLUTELY the first thing you should do.

So many times people just start throwing parts at the problem.

You Tube search "e46 Smoke Test"... there is a DIY test you can do that is super easy and uses less than $10 worth of materials and it 100% WORKS...

I had both lean bank codes and I did that exact test with the hand vacuum pump and the cigar. Found 3 small vacuum leaks in my intake plumbing. $25 for a new upper intake boot, and $5 worth of vacuum tubing fixed everything.

A full year and 10K later - no codes again EVER.

Not guaranteeing that you will have the exact same result; but the smoke test will allow you to see WHERE the leak is and which part(s) needs to be replaced.
Even if you have a larger repair like a DISA valve, the smoke test will confirm that the DISA is bad. Nothing worse than paying for high dollar parts only to find afterwards that you didn't fix the problem.

Smoke test first. Every time.

Last edited by BobC63; 12-06-2019 at 10:14 AM.
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Old 12-06-2019, 06:57 PM   #4
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You Tube search "e46 Smoke Test"... there is a DIY test you can do that is super easy and uses less than $10 worth of materials and it 100% WORKS...
We have a smoke test thread, linked inside the Important Threads and Links sticky.

How to Smoke Test
https://forum.e46fanatics.com/showthread.php?t=1261077
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Last edited by BaliDawg; 12-06-2019 at 06:58 PM.
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Old 12-08-2019, 06:58 AM   #5
bluetech
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Little update, Did the smoke test method with the cigar. The only thing I did find was a slight leak out of the DISA valve at the matting surface to the manifold. Nothing like a really big noticeable leak but hey it might be it. I will be taking care of it.

One other thing I did find when I took the air box out was my oil filter housing gasket leaking again. Now my question do you think that might be the cause of it? I know if you have a cracked valve cover or leaking valve cover gasket could cause lean codes. Just asking from others experience.

I did order all the parts to correct the issues I found. So this car will be down for a couple of days.
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Old 12-08-2019, 07:46 AM   #6
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No, the oil filter housing is under oil pressure. What brand of oil filter housing gasket did you buy? Also, did you torque the bolts to the correct values? Over-torquing crushes the gasket.
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Old 12-08-2019, 08:26 AM   #7
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The oil filter housing gasket was replaced almost 7 years ago. If I over torqued it, it wouldn’t have lasted that long. And it was BMW brand from the dealer when I bought it.


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Old 12-08-2019, 11:46 AM   #8
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Replacing the OFHG is a good time to replace the CCV parts, if they need it, as there is more room at that time.

I was going to recommend the Viton OFHG from ECS Tuning...
https://www.ecstuning.com/b-bavarian...21719855v~bav/
...which used to be cheaper from Bavarian Autosport...
https://blog.bavauto.com/17487/tired...-problem-ofhg/
...but now I see ECS has jacked up the price to $28!

For the replacement DISA o-ring, I like the fluorosilicone material best.
https://www.ebay.com/itm/111561787012
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Last edited by BaliDawg; 12-08-2019 at 11:47 AM.
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Old 12-08-2019, 12:40 PM   #9
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Thanks for the info. Can’t understand why they couldn’t put a regular O ring but instead use what looks like high temp RTV on the DISA valve. I was debating when I do the work to change the CCV. I actually have it home but never got around doing it. Maybe this is the time.


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Old 12-08-2019, 01:17 PM   #10
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Quote:
Originally Posted by bluetech View Post
Hey guys looking for some advise were to start. I got the other day my check engine light to come on. When I pulled the code I got P0174 lean bank 2. I did reset it once and after about almost 200 miles the light came back on. Both times the light came on while driving on the highway. When the light did come on I didn't notice any difference with the cars performance. Gas mileage seemed the same. I am going to look for the obvious things like a vacuum leak (torn intake elbow which was a cause previous). But that time I had lean bank 1 and 2. If anybody is wondering the fuel pump was replaced just last March and has less than 8000 miles on it.

I did pull the freeze frame off my reader and kind of confused me between bank 1 readings and bank 2 and that is why I am asking if somebody could look at it and see if it doesn't point to a vacuum leak. Maybe to something else like a MASS air flow sensor. As it is still original with over 250,000 miles on it.

Freeze Frame
FUEL SYS 1 CL
FUEL SYS 2 CL
CALC LOAD % 60.78
ECT 94c
STFT B1 -4.69
LTFT B1 8.59
STFT B2 10.94
LTFT B2 11.72
ENGINE RPM 2089
VEH SPEED 96KMH
SPARK ADV 15.00
IAT 3c
MAF g/s 35.86
TPS 29.80%
Change your pre_cat O2 sensor, rear exhaust manifold (4,5,6 cylinders) . My wife car had the same issue with code P0174.
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Old 12-08-2019, 01:38 PM   #11
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Originally Posted by bluetech View Post
Thanks for the info. Can’t understand why they couldn’t put a regular O ring but instead use what looks like high temp RTV on the DISA valve. I was debating when I do the work to change the CCV. I actually have it home but never got around doing it. Maybe this is the time.
Yeah, that was a questionable design decision BMW made on the DISA seal. Fortunately, the market found a solution in quality high-temp o-rings.

If you already have the CCV parts, then definitely do them at the same time. More room in there makes it much easier.

Maybe also check the VANOS oil line for seapage.
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Old 12-08-2019, 02:04 PM   #12
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Change your pre_cat O2 sensor, rear exhaust manifold (4,5,6 cylinders) . My wife car had the same issue with code P0174.
Replacing old high-mileage pre-cat O2 sensors is a good idea, but I don’t see anything in OP’s data that directly points to either being bad. The fact that the fuel system is in closed loop reporting fuel trims actually means they’re working. Those long term high fuel trims at idle are nearly always vacuum leaks that a diligent smoke test will expose.

Wouldn’t hurt to update the DME software though. See link below.
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Old 12-11-2019, 08:08 PM   #13
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today i joined the P0174 club (**at highway cruise same as OP) ..

i had noticed on the 04 xi the STFT both banks slowly climbing up to 15-16 over the last couple of weeks. so a vacuum leak and i see a smoke test and DISA re-seal in my future.

also the values are swinging wildly while driving, so i'm thinking about replacing oxygen sensors with NGK as well.

Quote:
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has anyone tried these NGK ... oxygen sensors (25569 and 25587)? better or worse than bosch/OE?
diagnostic report
highway cruise log

Last edited by wfx32; 12-11-2019 at 08:15 PM.
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Old 12-12-2019, 01:12 AM   #14
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today i joined the P0174 club (**at highway cruise same as OP) ..

i had noticed on the 04 xi the STFT both banks slowly climbing up to 15-16 over the last couple of weeks. so a vacuum leak and i see a smoke test and DISA re-seal in my future.
Running lean at highway cruise points more toward fuel starvation, whereas running lean at idle is usually vacuum leaks. The reason is that at higher RPMs/load a vacuum leak is much less significant because the air mass is much higher.
How’s the fuel pressure?
Is the fuel pump and filter fairly new?
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Old 12-12-2019, 06:16 AM   #15
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Running lean at highway cruise points more toward fuel starvation, whereas running lean at idle is usually vacuum leaks. The reason is that at higher RPMs/load a vacuum leak is much less significant because the air mass is much higher.

How’s the fuel pressure?

Is the fuel pump and filter fairly new?

that makes sense. i am already chasing fuel delivery as a possible cause of occasional misfire on the 05. the fuel filter and pump on the 04 are only about 5 years old.

i’d like to find a good solution for monitoring all of fuel, oil, coolant pressure from the cabin. not sure these can be taken from obd fusion, and maybe better to get a dme independent reading anyway. it might be time to look into some kind of race telemetry system.
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Old 12-12-2019, 03:28 PM   #16
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Originally Posted by BobC63 View Post
Smoke Test for PO171 / 174 codes is ABSOLUTELY the first thing you should do.

So many times people just start throwing parts at the problem.

You Tube search "e46 Smoke Test"... there is a DIY test you can do that is super easy and uses less than $10 worth of materials and it 100% WORKS...

I had both lean bank codes and I did that exact test with the hand vacuum pump and the cigar. Found 3 small vacuum leaks in my intake plumbing. $25 for a new upper intake boot, and $5 worth of vacuum tubing fixed everything.

A full year and 10K later - no codes again EVER.

Not guaranteeing that you will have the exact same result; but the smoke test will allow you to see WHERE the leak is and which part(s) needs to be replaced.
Even if you have a larger repair like a DISA valve, the smoke test will confirm that the DISA is bad. Nothing worse than paying for high dollar parts only to find afterwards that you didn't fix the problem.

Smoke test first. Every time.
Bob, it is P0171, not PO171. Reads the same, but much worse Google search results. One letter, 4 digits. The "0" indicates that it is a generic code (usually emissions) that applies beyond a single manufacturer.

https://www.obd-codes.com/faq/obd2-codes-explained.php
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Old 12-12-2019, 09:53 PM   #17
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swap pre-cat sensors and if you see error switches to another bank then you have O2 sensor bad. You don't need to remove them, just swap their connectors

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Old 12-12-2019, 10:08 PM   #18
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swap pre-cat sensors and if you see error switches to another bank then you have O2 sensor bad. You don't need to remove them, just swap their connectors
That doesn't work. You will get misfires. It is not like a coil. Those errors are "directional"... Plus you most likely have more than one cause for the code. Normal operating range is +/- 2%, and the code is thrown when >+11%, so there is usually more at play.
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Old 12-14-2019, 01:24 PM   #19
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Just swapping connectors on O2 is a fault condition and will not prove anything as Archbid says.

If you have an app which logs, I'd first check that the logged fuel trims are similar to the freeze frame. STFT fluctuates constantly.

Swapping sensors between banks should show a bad sensor if fuel trims follow the sensor. This takes 15 minutes at the most if you have a ratchet and crowfoot O2 socket. A fine tooth ratchet does help. Log and see what things look like.

With the two banks having substantial fuel trim differences the problem IMO is not something which affects all cylinders. To me, this means an O2 sensor, fuel injectors, plugs, ie bank/cylinder specific issues. Fuel pressure is equally distributed. Air flow is equally distributed. Either low fuel pressure or air leak will cause a smaller cylinder/bank related problem to be exaggerated. That is to say, if bank 2 O2 sensor is reading lean already, an additional air leak, dirty/under reporting MAF, or low fuel pressure may push trims far enough to throw a code. I think swapping upstream O2 sensors between banks is worthwhile for the time and cost involved.
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Old 12-14-2019, 01:25 PM   #20
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Just swapping connectors on O2 is a fault condition and will not prove anything as Archbid says.

If you have an app which logs, I'd first check that the logged fuel trims are similar to the freeze frame. STFT fluctuates constantly.

Swapping sensors between banks should show a bad sensor if fuel trims follow the sensor. This takes 15 minutes at the most if you have a ratchet and crowfoot O2 socket. A fine tooth ratchet does help. Log and see what things look like.

With the two banks having substantial fuel trim differences the problem IMO is not something which affects all cylinders. To me, this means an O2 sensor, fuel injectors, plugs, ie bank/cylinder specific issues. Fuel pressure is equally distributed. Air flow is equally distributed. Either low fuel pressure or air leak will cause a smaller cylinder/bank related problem to be exaggerated. That is to say, if bank 2 O2 sensor is reading lean already, an additional air leak, dirty/under reporting MAF, or low fuel pressure may push trims far enough to throw a code. I think swapping upstream O2 sensors between banks is worthwhile for the time and cost involved.
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