p2096 & p2196

[Vanne]

Post catalyst fuel trim system too lean bank1

And

O2 sensor signal stuck rich bank1 sensor1

Any ideas guys?
Car runs great, no issues at all.

[StickMon]

Sounds kinda like this:
z4m engine stutter

[Vanne]

thanks stickmon, but my engine is completely smooth..

possibly a bung O2 sensor?

thought id add, no CEL oe SEL lights either.

[Finnegan]

Tough set of codes.

One of the two O2s is probably bad, and the ECU can't get the fuel trim into a plausible range.

For example, if the primary O2 going bad (or gone bad) it's stuck showing a rich mixture. The ECU tries to adapt but that results in the secondary O2 reading a too lean condition. Basically it's like the primary "lying" and the secondary calling BS on it. Or it could be the other way around--I never think these things are as straightforward as they seem.

I'd check the wiring first. I think the only way to know for sure is to test voltage output ranges on the sensors. But I'm no expert on testing using voltage etc. (Other possible test mode is too swap front or rear left to right. If the code moves--or doesn't--that would tell the story. But for the effort it's probably easier to replace both.)

Pushing the car too lean isn't good for a happy or long engine life.

Other possible but less likely causes:

Bad or stuck injector(s).
Exhaust leaks.

If there's a good shop they could diagnose. But for an hour's labor you could just buy a new primary sensor (most likely). I'm not sure how smart the ECU is in its test algorithms. If the signal shows always rich on the primary no matter what it does to the trim then it would be the primary no question.

[Vanne]

Mate, Finn, nice diagnosis... that will give me something to play with.. what brand o2 sensor do you recommend? Possible a dirty maf? Haven't cleaned that since I got the car?

Also you mention exhaust leak, we talking at the manifold? I do sometimes seem to think I may have a leak there? Could that be the cause?

I've cleared the codes a few times, and def the same lean bank code pops up.

[Finnegan]

Leak would be a crazy thing like a hole in the header or a section post O2 sensor prior to the cat or a very bad gasket between sections (as in unlikely).

MAF is also possible, but if the error is one bank only it's unlikely it's the MAF. Can't hurt to try, but I'm more concerned with running it with these mixture issues.

O2? I'd go with OEM. You could look up the part number and see where to source the cheapest. Realoem is a great resource for that. Just double check that you're using the Euro part number. (The pre-cat O2 sensor should be the same between US and Euro, I think, but I'd hate to be wrong. That's why I mentioned it.)

[jliuod]

The pre-cat O2 sensor usually is the one that goes bad. At least in other cars. I thought BMW recommends replacing the O2 sensors as maintenance items?

[Vanne]

Finn, question if I may?


, but, the code shows a stuck O2 sensor on bank 1, now that's okay, I get that, and thus the system is driving bank 1 lean.. (not so good I know)

now from my time in Cessna's (yup, the whole range, from 210's all the way up to 404's) and leaning mixtures for a bloody long time, shouldn't my engine be running rough? , thing is its smooth as silk...

I know from rich to lean of peak which is the best , but then going leaner should/must result in rough running, and then even leaner in detonation..

I have no rough running...

or am I over thinking this and should just bloody replace the bank 1 pre cat O2 sensor

also just checked realoem, no changes between euro and us for this part, also it only shows one part number 11787540167, for the lamba O2 sensor..

http://www.realoem.com/bmw/showparts.do?model=DU91&mospid=49422&btnr=18_0661& hg=18&fg=10

on the S54, is there no different part number for bank 1 and 2?
pre cat, as in the picture, can someone confirm this is the correct part number?

[Finnegan]

Vanne,

Good questions and I don't have an answer. My earlier post suggested testing the voltage from the sensor during operation to see if the reading changed. If not, stuck seems plausible. The other possibility is that the secondary is off reading too lean and mis-coding the error. Or, the system is able to adjust trim within parms by ignoring the primary. Again, not sure what the ECU is capable of or what the diagnostic modes and test cycles are.

I wish I had more to offer on a test plan other than swapping primaries. If the error moves then you'd know it's the primary, if it doesn't move you know it's probably the secondary.

[sabbanick]

could be the cat too

[Vanne]

when we put my car on the lift yesterday, i noticed the egt sensor, the very bottom one hanging out under the car, the wires were broken and the sensor looks pretty beat up. (not sure why its position is right under the car in the exhaust, right where it can be damaged, but this sensor is busted. could that be the issue to throw those codes?

[Finnegan]

Originally Posted by Vanne

when we put my car on the lift yesterday, i noticed the egt sensor, the very bottom one hanging out under the car, the wires were broken and the sensor looks pretty beat up. (not sure why its position is right under the car in the exhaust, right where it can be damaged, but this sensor is busted. could that be the issue to throw those codes?

Fix the EGT, clear the codes and see.

The EGT determines when the cold and hot O2 main function (sensor test) runs iirc. Since the car runs fine the EGT could be throwing a spanner in the works and causing and erroneous set of error codes (error codes in error, lol).

[jdotketamine]

did we figure this out? i have the exact same codes on my n55 135i. the shop said it's the fuel injectors but im not buying it.