Service Engine light and Oxygen Sensors
 

My 'service engine soon' light is on and I've been reading up on possible causes. I will run the codes this weekend. I anticipate cleaning the MAF sensor, regardless, but since the CCV components were replaced 14 months/24k miles ago, just before I bought the vehicle, I'm assuming [perhaps erroneously] I won't have to do the CCV job. One possible source I've seen id'd is an oxygen sensor - and I see reports that replacing them [x4, parts cost maybe $280] as a 100k mile maintenance item. I'm overdue for that, if so, and need to do spark plugs, as well, due on the same schedule. Have any of you done the sensors as a 100k miles preventive maintenance item? I have viewed a couple of good videos on this DIY. Any tips on which codes point to the CCV/vacuum leaks, as opposed to the MAF or O2 sensors? Thanks in advance for any guidance.

Sorry to say, but this is waste of time without knowing the actual code.
It can be as easy as replacing fuel cap to vacuum leak, CPS, etc...

I've replaced all 4 O2 sensors (2 post, 2pre) bought from Amazon for $200.
When O2 sensor goes bad, it will shoot out very specific CEL code to indicate which one to replace.
If you are planning to DIY, make sure to have O2 socket tool.

As for vacuum leak, your best friend will be the smoke tester. Without that it's just guessing game.

So you would not recommend replacing O2 sensors without codes, even at high mileage?

My new-to-me 169k mile X5 with lots of repairs and not so much maintenance shows no record of O2 or spark plug changes. I'm doing the plugs (just like I'm on my way to doing all the fluids), but I usually only replace O2 sensors when there's a code. No running problems except that gas mileage on our first tank was only about 12 mpg (all city, 2001 3.0i). If I knew for sure that the O2 sensors were original I'd replace them. But there's a good chance they were replaced already and I just don't have the records. Also, the car has blown extremely clean smog check results for all of the 3 tests that I have records of.

Yes, read the codes first, it could be any single or combination of a big number of parts from the many subsystems that can trigger that light.

My SES just turned on as I type this, I just finished with the secondary air system and dmtl code...god knows what it is this time!

Preventive spark plug replacement at 100 k is always a good thing. O2 sensors also have approx 100k/10 year life.
As has been posted already, the first step is always, pull codes and perform the repair tree diagnostics aligned to any code that reappears after clearing the codes (record first then clear) and a short road trip. Hard failures will appear right away,depending on the part/ circuit.
Most poor economy, poor performance issues will be in the air intake, or ignition side of an engine. Plugs, o2 sensors, and CVCC systems are part of those areas. So the first step is good visual inspection of those areas, pull codes, and then look at specific parts/connections. If you find bad or lazy o2 sensors, one small tip is to hose them down with a WD-40 like product 24 hrs before you try unscrewing them from the exhaust system. If you have o2 codes it will be most likely to be the upstream (before the converter) sensor(s).

Good luck and post your codes if you need assistance.

My trusty Peake shows table 19, codes F5, F6, secondary air system flow too low, cyl 1-3 and 4-6. Autozone code reading shows codes PO491, 492, same description. I'll do a search for these codes, but any suggestions for the diagnostic tree to narrow this down? I'm leaning toward replacing the O2 sensors while I'm doing the plugs, even though I have no performance issues, as a 100k+ miles PM effort, but of course want to identify and fix the actual cause.

I found a pretty good DIY thread in another forum linking to a 2008 BavAuto newsletter article describing diagnostics for the Secondary air pump system, which generates these codes. I had to replace this 'smog pump' on my 1997 E36 convertible, so I've been here before. Hopefully, just a vacuum line fix, and if not, the check valve or [hopefully not] the secondary air pump itself. I would appreciate any links or info anyone can provide and I'll post my diagnostic process with links once done.

Ah, just went through this.

The bavauto link shows the earlier version of the secondary air system, wherein the air valve has a separate vacuum actuator system. Our trucks (2004-up 3.0) have the simpler version where the valve is simply pushed open by the secondary air pump air flow.

Usually if the pump is working (which you can check via the process in the bavauto link), the problem is the valve.

What is not commonly discussed online is at least one person has reported success in cleaning the valve.

Remove the valve from the exhaust manifold, spray some carb cleaner into the exit port of the valve, and allow to soak for a bit to work on the carbon. Then spray some more to rinse out. Repeat as necessary till it looks clean.

Re-install the valve (many people online reuse the gasket, its metal), reset the code, and hopefully that does the trick.

Sometimes people still have the code pop up after valve replacement even if the pump is working, which is resolved by a new pump. My guess is that the older pump has weakened enough to not push the needed amount of air. No sure way to diagnose as I've seen, till you are sure the valve is ok. Sort of a trial and error process. Most start trial and error with the valve because it's cheaper.

As I understand, you dont need to include the secondary air mass sensor and air cleaner in this troubleshooting process because since the code is a report that airflow is low, the AMS is working.

Good luck!

Now I feel like an idiot. After researching the codes Saturday, this morning I stopped to fill 'er up and, sure enough, I had lost the gas cap . . . duh. Light still on after I stopped by the BMW dealer en route to work [$48 replacement cap, but it does have the tether and 'bmw' stamped on it ....]. Hopefully, the missing cap was all it was throwing the codes. We'll see on the code reset. The good news: premium fuel down to $2.569 per gal at the Kroger with the Kroger 'frequent flyer' .03 discount. The teaching point: never underestimate the possibility of user error. Back in the day, the motor pool sergeant would call this a 'headspace and timing' problem.

Well... That's your choice. I guess with new O2 sensors, it will improve mpg little bit, but will it improve enough to justify cost of O2 sensors? I dunno.

Of course it's always good to perform preventive maintenance, but personally I wouldn't worry about them, especially with clean smog results.

Sure enough, reset the 'service engine soon' light with the trusty Peake and the warning is gone with my installing the replacement fill cap. So - if you get the service engine light and it kicks up the P0491, 492 codes, check the fill cap first!

haha so it was the gas cap after all... :D

Laugh if you must, but remember that I'm doing others a favor by passing on the tip, despite my embarrassment .... ;)

BTW, had to reset it twice, but now the service soon light stays off. I'm a big fan of the Peake code reader/reset tool, which I've had since maybe 2002....

Just a point of reference, my original pre-cat O2 sensors lasted 260,400 miles. The post-cat originals are still operating fine. The only consideration would be that I do stick with Shell gasoline 98% of the time and do not use any additional fuel additives.

2002 X5 3.0 268,450 miles
2004 325i 117,000 miles

That's good to hear, and is the sort of thing I was looking for with my earlier question. Did you get codes when they went? Did you notice anything with driveability or gas mileage before vs. afterwards that makes you think you should have replaced them before getting codes?

They are actually so cheap (like $50 each) and appear to be so easy to replace that I ended up ordering some and plan to replace them when I do the plugs in a few days. Both the O2 sensors and the spark plugs have no record of replacement, and I'm at 169k miles, so the lack of records (the PO gave me a binder of extensive repairs at dealers, etc. since 2004, but it is not 100% complete) on this is causing me to replace them. I do notice a general pattern of very expensive dealer-done repairs rather than preventive regular maintenance throughout the records.

My understanding is that the secondary sensors can definitely be run until getting a code without any concern. Right?

And hey, it's also great to hear of a 3.0 up at the high mileage you're at. Many more miles to go I hope.

oldskewel's is my original point regarding O2 sensors: some identify them as a 100k mile replacement item [like the plugs], but the post history here and on other forums suggest they have longer lives. When they go, what codes do they throw, and what are the performance indicators, if any? BTW, I may to go ahead and troubleshoot the secondary air pump system, as that evil 'service soon' light and codes return, even with a new $50 BMW gas cap. Sigh .....

They did trigger the SES light when they went. But I had noticed for about five days prior that the exhaust smelled "rich" at idle, even with a fully warmed up engine and my fuel mileage was down a half mile per gallon for that tank. Once that light comes on, you don't want to go too long before replacing the sensors, otherwise you'll be replacing the cats too.

2002 X5 3.0 268,600 miles
2004 325i 117,100 miles

srmm, do you recall what code was thrown with the 02 sensors issue? I'll try to look it up in the 'tables' book for my Peake, but those aren't the usual codes you see with std ODBII readers, and its not indexed by the fault description.

Sorry, but I don't have the software so I don't know what the code number was. I'm lucky to have a good relationship with the local dealer and their techs have never steered me wrong on a diagnosis so I have allowed them to do the major work on it. Plus they love bragging to their other service customer about how many miles are on mine and they've given me a 15% discount card on parts and labor to boot for several years now!

Update. I continued to get the Peake Table 19 F5, F6 codes [P0491,492 on Autozone's OBDII scanner] and added a table 19 3d code [post-cat O2 sensor] so I stopped by the dealer and had them do the official bmw computer scan. It tied the F5/F6 codes to the secondary air pump check valve and confirmed the one O2 sensor. The dealer's tech, always looking for billing opportunities, noted a leak around the valve cover gasket, too. The price quotes: $685 to replace one post-cat O2 sensor, $566 to replace the secondary air valve w/gasket, and $575 to replace the valve cover gasket. All easy DIY tasks, so I've ordered the parts [for these alone, less than $200, saving $1600+ over dealer rates] and will do the other O2 sensors and now-overdue sparkplugs while I'm under the hood. I don't notice symptoms, but I may do the preventative DISA valve repair [G.A.R. kit] while I'm at it. Any thoughts?

This is my humble 2 cents
(oem vs genuine parts your call)

- O2 Sensor
* Since one has failed, I plan to replace the other as well
- secondary air valve
* Try cleaning it 1st with carb cleaner or buy new one
* replace the gasket
* I will plan to do the hoses too, if it turns out to be brittle
- valve cover gasket
* Like you, I did the all the spark plugs at the same time.
* I added RR vanos high pressured oil line and gaskets
* refreshed CCV/Oil Separator (mine was an updated cold weather already but it been 9-10yrs) and included the updated guide tube+hose from Oil Separator to Guide Tube + Dip stick O-rings
* I did not do vanos o-rings and other parts by beisan, your call if you
are up to it -> Beisan Systems - Procedures - Double Vanos Procedure

- do visual check for other items like serpentine belts, ac belts, CCV/Oil Separator.....
- top off the fluids (collant, engine oil, power steering)


Hopefully, I can drive down there again this summer music festival and stone mountain for my little one (daughter).

GL...

My CCV pipes, etc [and the valve cover gasket] were done just before I bought it, less than 30k miles ago, so I expect the CCV is fine. I have ordered the OEM manufacture [but not BMW labeled] air control valve [p/n 11727553067] w/gasket for less than $100, Bosch O2 sensors x4, and the BRKR6EQUP plugs. I'll check everything out, but didn't plan to do the Beisan double Vanos o-ring replacement unless I had symptoms - vehicle is running great, what are the Vanos failure symptoms again? I'll pull the DISA and inspect its flapper, just trying to decide whether to go ahead and order the G.A.R. repair kit. As I understand it, the DISA is accessible from outside the valve cover, so no pressing need to do it while the cover is off. Regardless, between the plugs, O2 sensors, air control valve, and inspections [I'll probably pull and clean the MAF sensor, too], sounds like a fairly active Saturday of playing grease monkey ....