p0171 & p0174

[Ajcanadian]

Hey guys, so I've got an E39 530iA with almost 100k miles and all of a sudden the SES light comes on. I pull my cheapo OBD scanner and see P0171 & P0174 come up. I erase it and go home. By the time I back it in the SES light comes on. I hook the car up to PA BMW SOFT and erase the codes. 500 miles later the SES light pops up with the same code. My question is EVERY SINGE VACUUM LINE, CCV, PCV, Intake boot and Disa valve are replaced. Smoke tested the car and no vacuum leaks. Why would this come up? Is it because my fuel filter is almost clogged or a soft failing fuel pump? The car was in California till 2014 and maybe the 91 Gas could've taken a toll on the fuel filter?

[schatzy62]

If verified no air leaks. MAF or PreCAT O2 sensors. Unplug/Replug MAF and test. Many people report doing that corrects the problem. If codes come back clean MAF. Test again . If codes still come back O2 sensors.

[auaq]

There are couple of places to troubleshoot:

• Are you certain your CCV hoses are securely connected to the CCV? Check the front valve cover line that connects to the CCV. Mine wasn't secured properly and would easily pop out. That could potentially cause a vacuum leak.
• Have you inspected your secondary air injection vacuum hose that runs from the SAI valve and around the valve cover to the firewall side of the intake manifold? That hose is known for getting brittle due to heat, age and mileage, and easily cracks upon touch enough to cause a vacuum leak.
• Re check all of the recent work you did and ensure nothing is still loose or the rubber is torn apart especially at the y-split of the intake boot even though you did replace it.
• Any chance you have an oil leak coming from the valve cover? This can be another source for vacuum leak.
• Lastly, how old are your spark plugs? When was the last time you did a tune up? What do they look like? If they appear as pretty worn/used up and have some whit-ish colour at the tips or the electrodes, then it's time to replace them.

[Ajcanadian]

If verified no air leaks. MAF or PreCAT O2 sensors. Unplug/Replug MAF and test. Many people report doing that corrects the problem. If codes come back clean MAF. Test again . If codes still come back O2 sensors.

MAF reading was 18.00 according to PA BMW SOFT. I will try that

- - - Updated - - -

There are couple of places to troubleshoot:

• Are you certain your CCV hoses are securely connected to the CCV? Check the front valve cover line that connects to the CCV. Mine wasn't secured properly and would easily pop out. That could potentially cause a vacuum leak.
• Have you inspected your secondary air injection vacuum hose that runs from the SAI valve and around the valve cover to the firewall side of the intake manifold? That hose is known for getting brittle due to heat, age and mileage, and easily cracks upon touch enough to cause a vacuum leak.
• Re check all of the recent work you did and ensure nothing is still loose or the rubber is torn apart especially at the y-split of the intake boot even though you did replace it.
• Any chance you have an oil leak coming from the valve cover? This can be another source for vacuum leak.
• Lastly, how old are your spark plugs? When was the last time you did a tune up? What do they look like? If they appear as pretty worn/used up and have some whit-ish colour at the tips or the electrodes, then it's time to replace them.

All of the things you have mentioned I have checked and are new including the vcg.

However, the spark plugs did have oil residue on them. They are most likely the culprint

[auaq]

How bad is the oil residue on those plugs? The oil on spark plugs were most likely caused by the old-n-original worn out CCV. Keep in mind though M54 and M52tu piston rings are known for oil consumption but not all of them while some do. However, I don't think that's your main issue here. There's a possibility of some leftover pool of oil in the intake manifold. It might take some time to clear up, but anyways change your plugs and hopefully that should fix your lean codes.

[Ajcanadian]

How bad is the oil residue on those plugs? The oil on spark plugs were most likely caused by the old-n-original worn out CCV. Keep in mind though M54 and M52tu piston rings are known for oil consumption but not all of them while some do. However, I don't think that's your main issue here. There's a possibility of some leftover pool of oil in the intake manifold. It might take some time to clear up, but anyways change your plugs and hopefully that should fix your lean codes.

They looked a little oily but I've seen a lot worse on my first 530. That car had a bad CCv and the spark plugs in 12k mile where burnt that too with no abuse compared to that my current one is in a lot better shape. I will get that sorted out this week.

[koole39]

AjCanadian ... I just resolved the same codes on my 2002 bmw 530i. If this helps in anyway...

It started with P0171, P0174 and P1084.
First, I replaced both the oxygen sensors (mine were 2002 original) and this eliminated P0171 and P1084 codes.
I did a smoke test and found a small leak around the DISA valve area (replaced it with a new one rather than change seal etc.)
Given no leaks around the bellows and PCV area, I did not want to do un-necessary repairs.
For the remaining P0174, I also checked the bank2 spark plug chambers and the injectors. Everything seemed fine - clean - no signs of oil. Injectors were clicking properly.
Since the smoke test was solid after replacing the DISA valve, I did not want to risk opening the injection manifold.
But my suspicion was that the bank2 injectors were perhaps fouled up due to low grade fuel (My boss at home had accidentally filled 87 grade a couple of times).
So, I changed the fuel filter (again - replaced the original one) and gave my car a fuel injection treatment (techron) through the fuel tank.
My code P0174 code finally disappeared!!. The code readings on STTRIM1 and STTRIM2 are less than 1% on both on idle.
Earlier, the STTRIM2 (bank2) live data was running 20% higher than STTRIM1 (Bank1) which was giving the P0174 code.

Good luck with resolving these codes for your car!.
Have you done a smoke check? If so, recommend doing it after every part change just to check that a new leak did not show up.

[koole39]

Looks like you did a smoke test...just catching up on earlier posts... If your fuel filter/pump is original, consider replacing...
These codes are early for a car with 100K miles but you never know. Mine has 175K so - some of the original parts had reached end of life (and beyond).
If your car used low grade fuel earlier, it can cause problems... as seen in my case.

[Ajcanadian]

AjCanadian ... I just resolved the same codes on my 2002 bmw 530i. If this helps in anyway...

It started with P0171, P0174 and P1084.
First, I replaced both the oxygen sensors (mine were 2002 original) and this eliminated P0171 and P1084 codes.
I did a smoke test and found a small leak around the DISA valve area (replaced it with a new one rather than change seal etc.)
Given no leaks around the bellows and PCV area, I did not want to do un-necessary repairs.
For the remaining P0174, I also checked the bank2 spark plug chambers and the injectors. Everything seemed fine - clean - no signs of oil. Injectors were clicking properly.
Since the smoke test was solid after replacing the DISA valve, I did not want to risk opening the injection manifold.
But my suspicion was that the bank2 injectors were perhaps fouled up due to low grade fuel (My boss at home had accidentally filled 87 grade a couple of times).
So, I changed the fuel filter (again - replaced the original one) and gave my car a fuel injection treatment (techron) through the fuel tank.
My code P0174 code finally disappeared!!. The code readings on STTRIM1 and STTRIM2 are less than 1% on both on idle.
Earlier, the STTRIM2 (bank2) live data was running 20% higher than STTRIM1 (Bank1) which was giving the P0174 code.

Good luck with resolving these codes for your car!.
Have you done a smoke check? If so, recommend doing it after every part change just to check that a new leak did not show up.

Smoke test was done. I'm going to change the fuel filter first and go from there.

- - - Updated - - -

Looks like you did a smoke test...just catching up on earlier posts... If your fuel filter/pump is original, consider replacing...
These codes are early for a car with 100K miles but you never know. Mine has 175K so - some of the original parts had reached end of life (and beyond).
If your car used low grade fuel earlier, it can cause problems... as seen in my case.

Yes, it was smoke test. I am pretty sure low grade fuel was used in california

[Ajcanadian]

codes's haven't come up after replacing the sparkplugs