2008 E90 325i N53 3.0 NOX Sensor Heating Problem
Discussion
I've got a 2008 325i with the N53B30 3.0 Engine. One of the last of the Pre-LCI Models. Runs and drives absolutely beautifully, but I've got a problem with a fault code that keeps appearing.
It doesn't throw up any warning lights normally (but does occasionally after a while), but the fault code can be cleared and then reappears immediately on start up. It's BMW Fault Code 2B05, which is NOX Sensor Heating. Now I've got a very sophisticated Diagnostics Machine, which can read live data etc, and all 4 NOX Sensors are working exactly as they should be in terms of voltage before and after cats, mixture looks ok. Cats are pretty clean etc, but as it says "heating", that means either there's a wiring issue or one of the sensors has a faulty heating element in it, but from the fault code, I don't think it tells me which one, unless anyone else knows otherwise.
Any ideas from an BMW experts as to what I should be looking at? I can't see anything untoward in any of the live data streams I can pull off the diagnostics, but don't think there's anything specifically for heating that I can see. Any ideas what to look for? As said, voltage and mixture readings all look ok to me.
Thanks in advance!
It doesn't throw up any warning lights normally (but does occasionally after a while), but the fault code can be cleared and then reappears immediately on start up. It's BMW Fault Code 2B05, which is NOX Sensor Heating. Now I've got a very sophisticated Diagnostics Machine, which can read live data etc, and all 4 NOX Sensors are working exactly as they should be in terms of voltage before and after cats, mixture looks ok. Cats are pretty clean etc, but as it says "heating", that means either there's a wiring issue or one of the sensors has a faulty heating element in it, but from the fault code, I don't think it tells me which one, unless anyone else knows otherwise.
Any ideas from an BMW experts as to what I should be looking at? I can't see anything untoward in any of the live data streams I can pull off the diagnostics, but don't think there's anything specifically for heating that I can see. Any ideas what to look for? As said, voltage and mixture readings all look ok to me.
Thanks in advance!
Slight update. I gave the car a service and found 2 spark plugs loose and the rearmost coil pack not clipped in properly. There's also a plug on the cover you have to remove to get to the rear spark plugs (where the pollen filter sits on top of), which I think is something to do with the heater/climate control and I assume nothing to do with NOX Sensor heating, was also not connected properly.
Anyway, for now, that code doesn't reappear when I start the car. Not sure if any of the above could have affected that. I've got the car up in the air at the moment to change the rear shocks, so won't be able to take it for a drive for a couple of days now due to other things going on, but will see if it reappears upon driving.
I will do a NOX Cat Regen as well. Sulphur Saturation is 409mg, so not too high really, but it won't hurt.
Anyway, for now, that code doesn't reappear when I start the car. Not sure if any of the above could have affected that. I've got the car up in the air at the moment to change the rear shocks, so won't be able to take it for a drive for a couple of days now due to other things going on, but will see if it reappears upon driving.
I will do a NOX Cat Regen as well. Sulphur Saturation is 409mg, so not too high really, but it won't hurt.
I thought there was only one NOx sensor on the N53 engined cars. Aren't the four sensors you're referring to the four O2 sensors? AIUI if the NOx sensor is not working correctly the ECU will disable the lean burning modes, but the engine will otherwise run normally in "homogeneous" mode, hence the readings from the O2 sensors being fine.
Bimmerprofs have a lot of information on the N53 engine which may help.
Bimmerprofs have a lot of information on the N53 engine which may help.
Indeed it is separate, and diagnostics did show nox sensor in a separate section showing as inactive in the data stream, looking back at the photos I took of the data. Well that helps massively and I was being stupid then!
It is odd at the moment that the code was coming up on start up, but then wasn’t, as I didn’t disturb anything where it looks like that sensor is back towards the secondary cats, but guess it may reappear when driving. If the data still shows it as inactive then I guess that answers the question!
Thanks very much!
It is odd at the moment that the code was coming up on start up, but then wasn’t, as I didn’t disturb anything where it looks like that sensor is back towards the secondary cats, but guess it may reappear when driving. If the data still shows it as inactive then I guess that answers the question!
Thanks very much!
It looks like a box with a lambda probe coming off it. If it is the heating element that’s gone on it, might it be repairable with one of the generic lambda probes you can buy, or is that too risky as the heating may also be controlled by something inside the box?
I guess if it is still faulty then I’ve got nothing to lose by cracking it open and having a look, as if not then it’ll need replacing regardless.
I guess if it is still faulty then I’ve got nothing to lose by cracking it open and having a look, as if not then it’ll need replacing regardless.
So, I've changed the NOX Sensor, and that appears to be working now, but since changing it, it now throws up a new error code 3104 - Stratfied Mode Running Rough/Uneven.
So, I assume it hasn't been running in stratifed mode for a while, but now it is. Lots of info on Bimmerprofs, but nothing conclusive as many things can cause this it seems.
There are no real misfires or anything. I've cleared adaptations. It does seem to have a very slight hesitation at times. This was noticeable pulling away in 3rd gear beforehand. I mean very slight. Since changing the NOX Sensor it has become slightly more prominent. By that, I mean no worse, but it's like you can feel it slightly under light acceleration from low revs in 6th gear too. I think there was also a bit of fuel smell since running in stratified mode too. All of this seemed to disappear after clearing the adaptations, but then came back, along with the code.
Could the NOX cat need regenerating? It reads 450mg Sulphur at the moment. It did read 409mg last time I read it at the end of last week.
Any other ideas?
So, I assume it hasn't been running in stratifed mode for a while, but now it is. Lots of info on Bimmerprofs, but nothing conclusive as many things can cause this it seems.
There are no real misfires or anything. I've cleared adaptations. It does seem to have a very slight hesitation at times. This was noticeable pulling away in 3rd gear beforehand. I mean very slight. Since changing the NOX Sensor it has become slightly more prominent. By that, I mean no worse, but it's like you can feel it slightly under light acceleration from low revs in 6th gear too. I think there was also a bit of fuel smell since running in stratified mode too. All of this seemed to disappear after clearing the adaptations, but then came back, along with the code.
Could the NOX cat need regenerating? It reads 450mg Sulphur at the moment. It did read 409mg last time I read it at the end of last week.
Any other ideas?
Try an Italian tune up and make sure the tank is over half full and drive it at 50mph for half and hour or something like that to regen the nox trap. Bimmerprofs site has more on that procedure iirc.
Keep in mind that stratified works completely differently to homogenous injection as it's injecting multiple times on the compression stroke, and puts much more demand on the infection and fuel system being tip top than not. So it may be showing up other issues... weak spark, wrong plugs (only use correct NGK, not Bosch), iffy coilpack, weak battery, or worse a iffy injector with a duff spray pattern..
Keep in mind that stratified works completely differently to homogenous injection as it's injecting multiple times on the compression stroke, and puts much more demand on the infection and fuel system being tip top than not. So it may be showing up other issues... weak spark, wrong plugs (only use correct NGK, not Bosch), iffy coilpack, weak battery, or worse a iffy injector with a duff spray pattern..
Was just coming on to update. I think (and hope!) The only issue is the new spark plugs. After reading through some of the vast info on Bimmerprofs, I saw about the NGK plugs and the reasons why. It's just had Bosch ones fitted (Supplied by GSF from the reg and obviously not suitable). The coughing issue only appeared as far as I can tell after the new plugs were fitted, and was more prominent once stratified mode was working again, so makes sense. NGK ones to the correct part number ordered for tomorrow morning.
See what that does. I was going to force regen the NOX cat after all this was done anyway, but hopefully that'll cure the main issues and code 3104.
See what that does. I was going to force regen the NOX cat after all this was done anyway, but hopefully that'll cure the main issues and code 3104.
mbwoy84 said:
Was just coming on to update. I think (and hope!) The only issue is the new spark plugs. After reading through some of the vast info on Bimmerprofs, I saw about the NGK plugs and the reasons why. It's just had Bosch ones fitted (Supplied by GSF from the reg and obviously not suitable). The coughing issue only appeared as far as I can tell after the new plugs were fitted, and was more prominent once stratified mode was working again, so makes sense. NGK ones to the correct part number ordered for tomorrow morning.
See what that does. I was going to force regen the NOX cat after all this was done anyway, but hopefully that'll cure the main issues and code 3104.
Yeah mine ran a bit off with the Bosch ones. IIRC they are longer than the NGK too See what that does. I was going to force regen the NOX cat after all this was done anyway, but hopefully that'll cure the main issues and code 3104.
Update is, changing the plugs has cured the slight cough it had developed and seems to be running fine, but code 3104 still reappears after a short drive. It possibly smells quite “fuelly” at times standing outside the car with it running is the only observation, as it seems to run and drive exceptionally well to me.
Another bit of info, I’ve found an option in the live data stream that says “display operating mode”. At idle and coasting it shows Homogenous, and under any load it says homogenous_stratified_charge
Don’t know if that’s normal and if the latter means it’s in stratified mode or somewhere between the two, as it still says homogenous before it!
Don’t know if that’s normal and if the latter means it’s in stratified mode or somewhere between the two, as it still says homogenous before it!
It's now come back up with fault code for NOX sensor heating, albeit a different code.
On the status of the NOX Sensor, it now say "Dew Point Detection Expected", whch according to Bimmerprofs points to a faulty NOX sensor, but this is new!
With the old sensor, it just read "No Activity" and with the new one until now "Readiness Temperature OK".
The fuel pump plausibility code is coming up all the time now,.
On the status of the NOX Sensor, it now say "Dew Point Detection Expected", whch according to Bimmerprofs points to a faulty NOX sensor, but this is new!
With the old sensor, it just read "No Activity" and with the new one until now "Readiness Temperature OK".
The fuel pump plausibility code is coming up all the time now,.
Did another test drive as I read that the 2AAF relates to the low pressure fuel pump/sensor, and that if the pressure shot up and flatlined then look at the sensor. If it went down then look at the pump. Well, it did neither, but still flagged that code up (and that code only this time).
It states it should read 5000 HPA. Well, it was consistent, but was just under that. Approx 4700ish at idle. Driving never took it quite to 5000 either, 4900 and something was peak. Now it's thrown up the code based on that, as there were no spikes either way. Does it need to be at 5000? And if so, does that suggest sensor or pump.
That was the only code that came up this time. NOX Sensor status read Readiness: Temperature OK, BUT it was stuck in homogenous mode this time, which all seems a bit odd!
It states it should read 5000 HPA. Well, it was consistent, but was just under that. Approx 4700ish at idle. Driving never took it quite to 5000 either, 4900 and something was peak. Now it's thrown up the code based on that, as there were no spikes either way. Does it need to be at 5000? And if so, does that suggest sensor or pump.
That was the only code that came up this time. NOX Sensor status read Readiness: Temperature OK, BUT it was stuck in homogenous mode this time, which all seems a bit odd!
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