Pre-Cat Oxygen sensor?
 

The ones that are changed when something is amiss, which are they?

Try:

http://www.lambdasensor.com/main/bmw1.htm

Also knowing year and engine is useful...

Mine's a '08 3.0si. The webpage you posted doesn't list E70. Also it says front/rear but which is the pre-cat?

The diagram above is specific to my vehicle as it's from the realoem site, I put in all the info before going into detailed parts.

From the direction of the arrow in the diagram, I would guess that #1 and 2 are the pre-cat. The pre-cat sensor should be more in front and the post-cat sensors should be behind them. Have you had the codes read? They should tell you which "bank" and whether they are pre or post-cat.

With my engine light on, I checked and am getting some codes in my INPA tool for my 2008 E70 3.0Si:

2C3E A1 Lambda probe in front of catalytic converter 2, control failure or cable transmission failure?
2CA7 A1 Lambda probe heating in front of catalytic converter 2
2C9D A4 output heater O2-sensor before catalyst bank2

So, definitely looks to be pre-cat Lamdba. I'm a pretty good DIY'er, but haven't replaced a probe yet. I read that the pre-cat ones are easier. Any links to good pics/description of what's involved would be helpful if anyone has them. How can I tell which one is bank 2?

I can't tell from this diagram if it's number 1 or 2 that I need.

I found both parts (Bosch) on Amazon. Part 1 is a generic description, where Part 2 has in the description name "Oxygen Sender PRE-Cat Rear Manifold".

I would strongly suggest you find a WIRING DIAGRAM for your o2 sensor sand check EVERY fuse and connection....

When a car is started cold, the O2 sensors do not work- the car begins to warm up, AND the DME sends current to the O2 sensors (heater wihin the sensor) to get them up to temperature. If that circuit is damaged, you get an immediate "o2 heater circuit failure'. Each O2 sensor has 4 wires- one pair is hte acutal signal, the other pair is the heater circuit.

So check the connections first.

if you have 50k miles on them, you can go ahead and replace them- but if you just replace them and the error is there, you'll know what it is.

Also DO NOT wasted you money on OE BMW. Bosch OEM is perfect~$100.

Finally, the most important question: which bank is which? dunno. Sorry. Id replace both so it wouldnt matter to me.

Revising an old thread that I commented on. I let my engine light stay on for a while and finally took it in for other service to an indy and had him verify the codes. He found that the 2 "front" O2 sensors need replaced. His quote was $750 all in. Seems high, considering the parts are about $130-$150 each?

Based on the realoem diagram
RealOEM.com * BMW E70 X5 3.0si Lambda Probe Fixings

It looks like I need number 1 and number 2. But I'm still trying to find a good DIY with pics for a 2008 E70 3.0. Looking at my engine, it looks like there's a fair amount of stuff to remove first to get to both of them, but some guidance from anyone who's done it before would help.

What is the mileage of your X5?It is very rare both sensors to be bad,if not to say that it never happens.If,for example, there is a lean condition due to a vacuum leak,the ECU may throw a O2 sensor related code,but there is a difference between code pointing to the 02 sensor and bad 02 sensor.In the original BMW programs there are tests to be run to evaluate the condition of the sensors. If the Indy wants to replace both the technician has to show you the reason to be replaced or take responsibility if after spending $800 the problem persists.

almost 70,000 miles on it. I haven't picked the car back up yet. I agreed to some other work I needed done, so I'll ask him to elaborate more on how he determined that 2 needed replaced.

He told me both "front O2 sensors". I presume that to mean both "pre-cat" (though I'll double check this too), which if I understand right would be both on my left as I'm looking down at the engine. The one closest to the front I can see. I can't easily see the one further back towards the firewall, which makes me ask how much effort is involved moving things to get to it if I should do this myself?

+1

:iagree:

The sad truth is, however, that after he spends $750, and the problem comes back, then there will be ANOTHER issue, that "most likely is what caused the sensors to fail" for more $$$. Nobody EVER gives back cash for the poor diagnoses they perform (present company excluded. ;) )

(editorial comment: Nice....)

Anyway, how long is "a while"

I ask because it is rare to have 2 sensors fail at once..but you could have had one fail, turn the CEL on...and 20k miles later the other fails...

Sad true!!! There are no more people interested in daignosing a sick car,just ones that are interested in collecting $$$,as much as possible.I always go out of my way to make sure that the customer(or myself) doesnt buy parts that he doesnt need.That is not the best way to make living,but it is what it is.That is the reason i dont run a shop anymore.If you have $2500+ monthly expenses in rent and utilities and 1 GOOD WORKER(now that sounds really funny if it was not tragic) you cannot afford to let any customer to leave the shop with a bill smaller than $500 :rolleyes:
But back on track,I am ready to bet a substantial amount that with 70 k miles both pre-cat 02 sensors are in great health,except if something really bad happened,but I dont believe so.

The light came on about 11 months ago, or about 10000 miles of driving. I know, probably not smart. My gas milage didn't suffer though, if that's worth noting. I reset the service light a few times and it would come back on within 100 miles or less. Before the visit to the shop, I reset the service indicator again and it came on immediately after startup.

When you were doing these resets, did you pull any codes?

Pull codes when you can, post them. If you have a code reader that lets you look at short and long term fuel trims, post that too.

I only use the INPA and NCSExpert tools (and very limited at that).

Prior to my reseting of the service indicator the other day before going to the shop, the INPA codes were as follows:


00 JBBF OKAY 1 Error Stored
A6CF 28

12 DME/DDE OKAY 3 Error Stored
2C9D E4
2A99 81
2DEB 02
29 DSC OKAY 5 Error Stored
5F45 A0
6EC8 A0
6EBD A0
5F13 A0
6D9E A0
36 TEL OKAY 1 Error Stored
D691 20

55 ISPB OKAY 1 Error Stored
D351 20

5E GWS OKAY 1 Error Stored
A83A 22

60 KOMBI OKAY 1 Error Stored
A3B1 20
62 MOSTGW OKAY 1 Error Stored
E18F 20

6E BFS OKAY 1 Error Stored
9E84 21

These would be the ones that set a CEL, actually I think just the first two.

One is an O2 sensor HEATER code, which means the wire to the O2 is disconnected or the fuse is blown or the sensor massively failed.

Check all connections to the O2 sensors- pop them apart and reconnect them.

Second code i2a99 is an exhaust camshaft correlation. Im guessing a camshaft position sensor? The other issue can be a sluggish VANOS solenoid. Usually due to fouling of the solenoid due to BMWs horrific oil change intervals. Pop them out, flush/clean them, replace Orings.... at least on E39s.

Last one I dunno- seems like a battery issue. How old is you battery? Any charging/voltage issues?

Battery is at least 2 1/2 years old (when I bought the car with 30,000 miles on it). I don't see anything in the carFax indicating a battery change, which doesn't mean it wasn't done of course but I see a lot of other standard routine maintenance logged by dealerships where the prior owner took it.

In the cold, it does *slightly* stutter when starting the engine, but otherwise I've had no indications of a bad battery otherwise. If it is original, it may be in need of a replacement, which also means coding the new one if I'm not mistaken, right?

Almost surely original. No idea what ear or model engine you have....

Replace it with an idential battery and ALL you need to do is "register" it. And even that isnt essential. Youve got the tools to do it I think.

Thanks for all the feedback. Car is an 08 3.0 model with an N52 engine. Other than sometimes the stuttering to start when cold, or after sitting a week unused, I haven't seen any other signs of battery weakness.

These days the BMWs do odd stuff with voltage regulation and charging..I believe the voltage is allowed to drop too low after starting but during operation and this can throw off odd errors from some modules. just weird random modules with faults. You wont notice running issues but the stuff hanging on the bus will not be happy.

Just wag.

Absolutely!It is probably just a random code.
As a matter of fact the computer is monitoring the voltage of the battery and the current that is drawn and if the voltage drops too quickly it will throw a code and warning light.It may not come back for a long time.I have had some stored in my car's memory,but the car will start after being parked for 2 weeks.

Question:

Will it show the 'workshop service' warning? Like this:

http://img.photobucket.com/albums/v4...2/P1000993.jpg

but not a CEL??? (Which is the classic 'yellow engine symbol')

I am really not sure if accelerated battery discharge will show the "workshop service",but for sure it will not trigger CEL,except there are some major power supply issues.

I think it shows a battery in the gauge cluster but the lift in the NAV screen.

Updating the thread...I finally replaced the sensor. It was the pre-cat, bank 2 sensor. Nothing else. Engine light stayed off after the replacement, and none of the prior codes have come back.

But this is not an easy DIY for this model car (2008 E70). It's extremely difficult to get to the pre cat 2nd bank (rear) O2 sensor, and even more difficult to get the wire routed to the plug because it goes around the back of the engine. Looking down at the engine, the sensors are on the left down under the spark plugs. You can see the bank 1 pre-cat sensor fairly easily. The bank 2 sensor is under a shield that has to be removed. The wiring from the probes goes around the rear of the engine to the connectors on the rear right side (looking down at the engine and into the back with a flashlight).

I had the car in an indy shop for front left suspension work and provided the mechanic the probe to install for me. He did it in about an hour, and that was because he had a lift to jack the car up over his head so he could easier get to the wiring. But not after he had to remove most of the components on top of the engine and around the firewall to also get to the probe and connectors.

Probe was about $130. His labor was another $100'ish. Money well spent because I would have been cussing and swearing every second I was trying to do that myself.

PHL08 - sent you a pm on this. Where'd you get the oxygen sensor for $130 and do you have the part number? Thanks!!!

Replied privately, but for others needing this same part..

Bosch 11787558081

I got it from a dealer on eBay. But just googling that above term reveals lots of sellers (at higher prices, too).