[TangoAlpha]

Hi guys, I've been having catalytic converter/Nox/O2 sensor issues with my N43 E93 which I've been having a hard time getting a conclusive diagnosis for.

I bought the car about a year ago at 67k miles and I've had code P122F (Nitrogen Oxide Sensor Binary Oxygen Sensor Short Circuit) intermittently. I got code P114C (Post Catalyst Fuel Trim Via Oxygen Sensor System Too Rich Bank 2) shortly after buying the car, however this didn't come back after clearing the codes.

A few months after buying the car, I'd occasionally see a puff of smoke coming from under the bonnet after the engine warmed up. A leak in the valve cover gasket was causing oil to drip on the exhaust header. Replacing the gasket has fixed this, and while I don't think the engine was burning oil and I certainly didn't notice huge puffs of blue smoke out of the back, I don't know for sure that it wasn't - which I gather isn't good for the catalytic converters.

In addition to the recurring P122F, I now have codes P0420 and P0430 (Catalyst System Efficiency Below Threshold Bank 1/2). I also have code P114D (Post Catalyst Fuel Trim Via Oxygen Sensor System Too Lean Bank 2).

The freeze frame data from the last P122F code is as follows:
- ETC 60°C
- RPM 1769
- VSS 32km/h
- Spark adv 3°
- MAF 3.91g/s
- Runtime 844 seconds
I've omitted some of the other available values, let me know if any additional ones would be useful.

Worth noting is that the engine doesn't seem to run all that hot (by BMW standards!) and I'm not sure it ever goes above 95. I did have the water pump replaced about 6-7 months ago and prior to that the engine did run at 105 regularly. From my reading, if it's not running hot enough it'll burn rich, which can damage the cats. I haven't been keeping such a close eye on the temps lately because it's such a faff to unlock the 'secret' menu in the dash (the E93 has a MPG dial in the cluster instead of a temp gauge).

Fuel economy also seems a bit on the low side: about 27mpg in town, up to 32mpg on the motorway if I'm driving very conservatively. I'm starting to wonder if maybe the engine is never running in stratified charge mode? Performance generally seems ok though, no obvious rattling sounds and generally the engine seems to runs smooth, though maybe a little rough at idle from a cold start.

I was initially minded to replace the Nox sensor (or get a Noxem), but seeing as it's a £400 part + labour, I'd like to make sure it's the right thing the do, and every mechanic I've spoken to and thread I've read have suggested different causes/solutions:
- replace the Nox/O2 sensors
- run on premium fuel to warm up/clean out the cats (I've done this a few times and it doesn't seem to have had any effect)
- injector issues
- exhaust leak
- replace the cats/bang them with a mallet to see if they rattle (can't say that diagnostic process fills me with confidence!)
- Decat exhaust headers (I'm disinclined based on the hassle come MOT time and the effect on the resale value, although I do wish the car sounded a little more 'throaty')

I do a fair bit of long, fast motorway driving so the cats should be in good shape (the car currently has 74k miles on it). I gather they usually last 100k+, so I'm loathe to replace them if they're still good, but on the other hand the sensors look like they'd cost nearly as much - and I'd rather not replace both.

I'm also a bit unclear as to whether the car has a 3rd cat? I can see two under the engine on the tail end of the exhaust headers (which looks like a pain to get to/ditto the sensors), but I'm not clear whether the thing halfway down the exhaust pipe under the car is another cat, or a muffler?

Any advice on how to further diagnose the problem would be greatly appreciated and I'm happy to provide any further info if I can.

Thanks,
TA.

[therealdb1]

Is your car asking for a new thermostat?
Running hot is bad but running cool is not good either!

[TangoAlpha]

Originally Posted by therealdb1

Is your car asking for a new thermostat?
Running hot is bad but running cool is not good either!

No codes relating to the thermostat and it should be fine as it was replaced at the same time as the water pump about 6 months ago. I am wondering if the engine is running cold because it's never going into stratified mode especially in view of the fuel economy, but I'm not sure how I can check?

[therealdb1]

Nothing to do with stratified or turbulent if the engine is not up to temperature it is probably the thermostat stuck open.

Six-month old parts can fail and not every fault on a BMW will show a code.

Do the pfaff on the instrument panel and see what the temperature of the engine is after a run to confirm and if it is only 60 degrees when the ambient is what, 15 degrees at the moment, you almost certainly need a new thermostat.

Until you get the engine running at the right temperature there is no point in worrying about emissions and fuel consumption since it will be overfuelling because it hasn't warmed up yet.

Incidentally, my 335i does have a dashboard temperature gauge but it measures oil temperature and it takes about 48 hours to get up to proper temperature so it is next to useless anyway and you have to find alternative ways to check the water temperature.

Funny thing is my Porsche has oil and water temperature gauges and the oil one lags the water one by about half an hour. What is the point?

[TangoAlpha]

Thanks - I will keep a closer eye on it and report back, but I'm sure it's above 60. I plug my obd reader in after driving once in a while and it's usually 85+, so I think it's around 90-95 while driving most of the time. My understanding is that the norm for these engines is closer to 105 though, and it certainly was prior to having the water pump replaced.