O2 Sensor Heater Code N54

BadContrakt · 06-12-2019, 10:41 AM

2008 N54
Catless downpipes installed a few weeks ago
Tuned MHD stage 2

I reinstalled the front O2 sensors and all is well there
I did not reinstall the rear sensors, instead, I bunged them shut with the provided threaded bungs.

My coder tells me he coded out the rear O2 sensors. I drive it. CEL comes on. Hmmm. He checks the code and it's for both post-cat O2 sensor heaters.

The car is not throwing a code regarding emissions, it's throwing a code for faulty heaters. What's the right move here?

type-dRew · 06-12-2019, 10:46 AM

Install the sensors.

BadContrakt · 06-12-2019, 10:51 AM

Quote:

Originally Posted by type-dRew

Install the sensors.

I was sure thinking this would be an option but I'd rather not if I don't have to.

I'm hoping someone has a good coding answer lol.

BadContrakt · 06-12-2019, 10:52 AM

Quote:

Originally Posted by type-dRew

Install the sensors.

Maybe this sounds ridiculous or maybe it doesn't, idk, you tell me.

What if a guy just plugged the sensors in and zip tied them somewhere underneath? Do they get hot enough to light stuff on fire underneath the car?

nissubaru · 06-12-2019, 10:52 AM

Install the o2 sensors, what he coded out just prevents a different CEL from popping up because youre catless and the car will know. The CEL you're getting now is because you have no sensors.

type-dRew · 06-12-2019, 10:54 AM

The dme requires the rear o2 sensors for the fuel trims to be accurate. It's a checks and balances thing.

Installing them in fresh air would just fuck up your trims horribly.

BadContrakt · 06-12-2019, 11:06 AM

Quote:

Originally Posted by type-dRew

The dme requires the rear o2 sensors for the fuel trims to be accurate. It's a checks and balances thing.

Installing them in fresh air would just fuck up your trims horribly.

I wonder why they offer the bungs if the rear O2 sensors have anything to do with fuel trims. I thought in like... every car... The pre-cat sensors do all that. I thought post-cat sensors were only there because the government wants to make sure our cats are functioning.

type-dRew · 06-12-2019, 11:48 AM

Quote:

Originally Posted by BadContrakt

I wonder why they offer the bungs if the rear O2 sensors have anything to do with fuel trims. I thought in like... every car... The pre-cat sensors do all that. I thought post-cat sensors were only there because the government wants to make sure our cats are functioning.

My last two cars would fuck up fuel trims and run completely different if I removed the post cat o2 sensor. This is not unique to the n54.

They include the block offs to appease people and because people who make downpipes do not know the inner workings of the DME and dont care if removing them does or does not have an affect on how it runs.

BadContrakt · 06-12-2019, 11:49 AM

Quote:

Originally Posted by type-dRew

My last two cars would fuck up fuel trims and run completely different if I removed the post cat o2 sensor. This is not unique to the n54.

I don't believe the rear o2 sensors are too bad to install. I'll probably just throw them back under the car and be done with it.

dpaul · 06-13-2019, 06:01 AM

type-dRew is correct.

While some have reported no difficulties after removing post-cat sensors, other report significant, undesirable changes in fuel trims. Apparently, since the post-cat sensors are narrow band, they provide a very accurate reference voltage around the optimal stoichiometric ratio of fuel/air (aka lambda = 1.0). That is, the output voltage changes dramatically and in a very non-linear fashion above and below stoich. The pre-cat wide-band sensor output varies in a different fashion, allowing them to accurate report small changes in oxygen content but as a consequence are not as accurate at lambda = 1.0.

Thus, the post-cat sensors are used as a reference by the DME to calibrate the pre-cat sensors to lambda 1.0. At least that is the explanation I was given on another forum.

When your "coder" said he "coded" out the rears, perhaps he meant he disabled the cat efficiency monitors, which is what most tuners do. That would not protect against a CEL if the sensors were completely removed, although it is possible to disable enough monitors that the CEL could be eliminated. In any case, there's a checkbox in MHD to disable cat efficiency monitors so it doesn't require a tuner or coder

dpaul · 06-13-2019, 06:09 AM

Quote:

Originally Posted by BadContrakt

I wonder why they offer the bungs if the rear O2 sensors have anything to do with fuel trims. I thought in like... every car... The pre-cat sensors do all that. I thought post-cat sensors were only there because the government wants to make sure our cats are functioning.

I thought that too. But it is apparently not the case

But I have to admit I am still confused about why post-cat removal causes trim issues for some but not others.

type-dRew · 06-13-2019, 06:34 AM

Quote:

Originally Posted by dpaul

I thought that too. But it is apparently not the case

But I have to admit I am still confused about why post-cat removal causes trim issues for some but not others.

I'd imagine the people who say it doesn't affect them simply aren't watching the trims. The car doesn't throw codes and makes full boost so its 'fine'

dpaul · 06-13-2019, 06:44 AM

I'd buy that explanation except that one of the posters reporting no issues is someone who really knows quite a bit about tuning, software and electronics.

However, in my searches, there were certainly more with trim issues than not. So perhaps the simplest explanation is that the calibration hypothesis is real.

type-dRew · 06-13-2019, 07:51 AM

Was the one reporting no issues perhaps one with an older 'dumber' DME version?

BadContrakt · 06-13-2019, 08:24 AM

Quote:

Originally Posted by dpaul

When your "coder" said he "coded" out the rears, perhaps he meant he disabled the cat efficiency monitors, which is what most tuners do. That would not protect against a CEL if the sensors were completely removed, although it is possible to disable enough monitors that the CEL could be eliminated. In any case, there's a checkbox in MHD to disable cat efficiency monitors so it doesn't require a tuner or coder

Correct. My car doesn't throw any cat codes. Just heater codes. So his coding worked. And when I tuned MHD I saw nothing in the check boxes for cat codes. I don't believe that's true. I think they USED to do it but they do no longer.

type-dRew · 06-13-2019, 08:35 AM

Quote:

Originally Posted by BadContrakt

Correct. My car doesn't throw any cat codes. Just heater codes. So his coding worked. And when I tuned MHD I saw nothing in the check boxes for cat codes. I don't believe that's true. I think they USED to do it but they do no longer.

No its still there, you just select 'stock downpipes/cats' option and the cat codes wont be turned off. If you dont select that every OTS MHD map has the cat efficiency codes disabled.

dpaul · 06-13-2019, 08:40 AM

Quote:

Originally Posted by type-dRew

Was the one reporting no issues perhaps one with an older 'dumber' DME version?

Good thought - don't know the answer, will try to find out.

dpaul · 06-13-2019, 08:42 AM

Quote:

Originally Posted by BadContrakt

Correct. My car doesn't throw any cat codes. Just heater codes. So his coding worked. And when I tuned MHD I saw nothing in the check boxes for cat codes. I don't believe that's true. I think they USED to do it but they do no longer.

As type-dRew reports, MHD still has it - it's the JB4 system than no longer provides this functionality.

BadContrakt · 06-13-2019, 09:24 AM

Quote:

Originally Posted by type-dRew

No its still there, you just select 'stock downpipes/cats' option and the cat codes wont be turned off. If you dont select that every OTS MHD map has the cat efficiency codes disabled.

Quote:

Originally Posted by dpaul

As type-dRew reports, MHD still has it - it's the JB4 system than no longer provides this functionality.

Hmmm good to know for future reference. I don't need it anymore but now I know right?

Brandxnvv · 08-28-2019, 01:49 PM

Installed me front 02 sensors & left my rear ones out. Have a jb4 in my vehicle and it goes into safety mode (map4) automatically. It was doing it before I put the catless downpipes in as well but I thought installing downpipes would fix it. It was a front 02 code. If I get a pre cat 02 sensor would the jb4 stop going into safety mode?

BadContrakt · 09-16-2019, 09:46 AM

Quote:

Originally Posted by Brandxnvv

Installed me front 02 sensors & left my rear ones out. Have a jb4 in my vehicle and it goes into safety mode (map4) automatically. It was doing it before I put the catless downpipes in as well but I thought installing downpipes would fix it. It was a front 02 code. If I get a pre cat 02 sensor would the jb4 stop going into safety mode?

Hmmm totally depends on what the code is. I don't know much about JB4 either as I don't run one. Maybe someone else can pitch an idea. You should tell us what code exactly it is.

type-dRew · 09-16-2019, 10:41 AM

Quote:

Originally Posted by Brandxnvv

Installed me front 02 sensors & left my rear ones out. Have a jb4 in my vehicle and it goes into safety mode (map4) automatically. It was doing it before I put the catless downpipes in as well but I thought installing downpipes would fix it. It was a front 02 code. If I get a pre cat 02 sensor would the jb4 stop going into safety mode?

Uh, did you install new front sensors when you did downpipes?

If not, why did you think downpipes would fix the issue but new sensors wouldn't?

You need new front sensors and to re install your rear sensors.

06-12-2019, 10:41 AM	#1
BadContrakt Private First Class 73 Rep 135 Posts Drives: 2008 E90 335XI Join Date: Oct 2018 Location: Florida iTrader: (0)	O2 Sensor Heater Code N54 2008 N54 Catless downpipes installed a few weeks ago Tuned MHD stage 2 I reinstalled the front O2 sensors and all is well there I did not reinstall the rear sensors, instead, I bunged them shut with the provided threaded bungs. My coder tells me he coded out the rear O2 sensors. I drive it. CEL comes on. Hmmm. He checks the code and it's for both post-cat O2 sensor heaters. The car is not throwing a code regarding emissions, it's throwing a code for faulty heaters. What's the right move here?
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06-12-2019, 10:46 AM	#2
type-dRew Major 641 Rep 1,245 Posts Drives: 2009 335i xDrive Join Date: Feb 2019 Location: Newport MI iTrader: (0)	Install the sensors. __________________ 2009 335i xDrive AT / 177k+ miles PSP 750ic / Fuel-It! Stage 1 / BMS CP / Sutphin Tuning / RFP E50 11.61 @ 117.5 New setup; Covid 19Ts on RFP 93 + ARM inlets, dp, VTT cp and PSP outlets
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06-12-2019, 10:52 AM	#5
nissubaru Lieutenant 233 Rep 564 Posts Drives: 09 335i MSport + 1990 300ZX TT Join Date: Jan 2017 Location: Philadelphia iTrader: (0)	Install the o2 sensors, what he coded out just prevents a different CEL from popping up because youre catless and the car will know. The CEL you're getting now is because you have no sensors.
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06-12-2019, 10:54 AM	#6
type-dRew Major 641 Rep 1,245 Posts Drives: 2009 335i xDrive Join Date: Feb 2019 Location: Newport MI iTrader: (0)	The dme requires the rear o2 sensors for the fuel trims to be accurate. It's a checks and balances thing. Installing them in fresh air would just fuck up your trims horribly. __________________ 2009 335i xDrive AT / 177k+ miles PSP 750ic / Fuel-It! Stage 1 / BMS CP / Sutphin Tuning / RFP E50 11.61 @ 117.5 New setup; Covid 19Ts on RFP 93 + ARM inlets, dp, VTT cp and PSP outlets
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06-13-2019, 06:01 AM	#10
dpaul Lieutenant Colonel 654 Rep 1,893 Posts Drives: 2009 E90 335xi, 2011 E93 M3 Join Date: Dec 2012 Location: Boston iTrader: (3)	type-dRew is correct. While some have reported no difficulties after removing post-cat sensors, other report significant, undesirable changes in fuel trims. Apparently, since the post-cat sensors are narrow band, they provide a very accurate reference voltage around the optimal stoichiometric ratio of fuel/air (aka lambda = 1.0). That is, the output voltage changes dramatically and in a very non-linear fashion above and below stoich. The pre-cat wide-band sensor output varies in a different fashion, allowing them to accurate report small changes in oxygen content but as a consequence are not as accurate at lambda = 1.0. Thus, the post-cat sensors are used as a reference by the DME to calibrate the pre-cat sensors to lambda 1.0. At least that is the explanation I was given on another forum. When your "coder" said he "coded" out the rears, perhaps he meant he disabled the cat efficiency monitors, which is what most tuners do. That would not protect against a CEL if the sensors were completely removed, although it is possible to disable enough monitors that the CEL could be eliminated. In any case, there's a checkbox in MHD to disable cat efficiency monitors so it doesn't require a tuner or coder Last edited by dpaul; 06-13-2019 at 06:08 AM..
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06-13-2019, 06:44 AM	#13
dpaul Lieutenant Colonel 654 Rep 1,893 Posts Drives: 2009 E90 335xi, 2011 E93 M3 Join Date: Dec 2012 Location: Boston iTrader: (3)	I'd buy that explanation except that one of the posters reporting no issues is someone who really knows quite a bit about tuning, software and electronics. However, in my searches, there were certainly more with trim issues than not. So perhaps the simplest explanation is that the calibration hypothesis is real.
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06-13-2019, 07:51 AM	#14
type-dRew Major 641 Rep 1,245 Posts Drives: 2009 335i xDrive Join Date: Feb 2019 Location: Newport MI iTrader: (0)	Was the one reporting no issues perhaps one with an older 'dumber' DME version? __________________ 2009 335i xDrive AT / 177k+ miles PSP 750ic / Fuel-It! Stage 1 / BMS CP / Sutphin Tuning / RFP E50 11.61 @ 117.5 New setup; Covid 19Ts on RFP 93 + ARM inlets, dp, VTT cp and PSP outlets
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08-28-2019, 01:49 PM	#20
Brandxnvv New Member 0 Rep 6 Posts Drives: 2008 bmw 335xi n54 Join Date: May 2019 Location: New York iTrader: (0)	Installed me front 02 sensors & left my rear ones out. Have a jb4 in my vehicle and it goes into safety mode (map4) automatically. It was doing it before I put the catless downpipes in as well but I thought installing downpipes would fix it. It was a front 02 code. If I get a pre cat 02 sensor would the jb4 stop going into safety mode?
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