About two weeks ago my check engine light came on. had it checked with my Ind. Mechanic and one bank was running lean. He reset it. them about a week later the light came on again. this time both banks were running lean. What are we looking for? Do we have a Vacuum leak? bluewagon
My Recent Experience I had been having the same issue with my 2000 540iA (I think the codes were PO171 and PO174-lean banks 1 & 2) so the first thing you want to do is check for vacuum leaks. Many have solved this problem by discovering a small tear on the intake tube or somewhere else but it is usually associated with a vacuum leak, which is the least expensive fix. The next thing to check will be the MAF/HFM5, which can be bad but not throw any codes. Ask me how I know...yup, mine turned out to be the HFM5 since a vacuum leak was not my issue. Make sure you clear any codes before you begin so that you will know if the lean bank goes away when it's time to test your ride. From there, it gets a bit more complex but you can find and DIY most vacuum leaks so that should get you started in the right direction. If you don't find any vacuum leaks then try disconnecting the MAF and see if the lean bank goes away. That was the case for me so I replaced the HFM5 for $80 and the problem is solved... GL and keep us posted as to your results... BTW, a great program to use when encountering these issues is the OBDCOM2. It is an excellent and inexpensive way to troubleshoot your BMW without spending the big bucks for an inshop diagnosis AND it allows you to clear your CEL and SES as long as you have a laptop...peace.
check engine soon I have changed the Mass air flow sensor about two months before the lights came on.But between then I did change the air filter.Idid vacuum out the air filter housing. Iwonder if a small particle of dirt did get through.and get on to the m.a.f.s . bluewagon
Good info... OK...can't be the MAF if you replaced it, however, I have heard of others getting bad replacement MAFs. Was it an OEM replacement or aftermarket? Remember that you can still disconnect the MAF after clearing the codes just to be sure but be aware that it will probably cause a MAF code since it's disconnected. I also doubt that vacuuming out the air filter housing would cause this problem but looking at the MAF is an easy task so if you have a Torx 25 security bit, you can look to see if there is any debris in there...doubtful though since there is a fine screen pre-MAF. BTW, it really helps to have your own diagnostic tool i.e. OBDCOM and as simple as it may be, it gives you more control over situations like this. You can read and clear codes at a whim, which makes troubleshooting a lot less painful. My rough idle went away and so did the lean bank codes after replacing the HFM5 (MAF). I've also recently successfully repaired the CCV ($550-quote $55 online and one hour-actual cost) and ABS/DSC module ($1350-quote and $320-rebuild by ModuleMaster and 5-day turnaround) because I was able to read the codes myself, which aided me in my troubleshooting task. At this point, I'm gonna suggest that it's a vacuum leak on the intake boot because that is the most common one but it could be somewhere else. I believe your shop can hook up an HVAC, which introduces smoke into the system making it easy to identify a vacuum leak. Keep on it and we'll get your dashboard cleared of that nasty CEL...I know I'm quite happy to have a clear dash again especially since I went through the x-mas tree light show when my ABS/DSC module failed. GL...
Tools The Peake code reader is a great little tool, doesn't require a laptop and many BMW enthusiasts are familiar with it, making it easier to search the Internet for similiar issues with the same codes. I would also suggest that you list the year and model of your car when posing questions. Certain models have unique "common issues" that might help others quickly diagnose your problem(s). And I was most amused by the title of your post. "Check Engine Soon" light. Ha! Funny. You probably meant "Check Engine" or "Service Engine Soon" but your combination of them is much more entertaining! Michael
My 2001 325xiT is displaying the Service Engine Soon light on the instrument cluster. Just to be clear, it is NOT the Check Engine light, it is the Check Engine Soon light. I have replaced all of the fluids, checked the OBD II, and no codes show. I've heard that the Check Engine Soon light comes on around 100,000 miles as a way to give my local dealer some business. I've performed the services that would be done at 100,000 miles by the dealer. Can anyone tell me how to reset the Check Engine Soon light?
+1 on the Peake code reader. It has come in handy many times. I use it as a 'guide' and do not always take the information as 'absolute'. Case in point: Service Engine Soon light came on and the code indicated a failed secondary air pump but the actual problem was a vacuum leak in a very small hose that runs next to the valve cover.
