Fault codes, need help!

[ExoticM3]

2740: Lambda sensor heating control diagnostic VKAT bank 1

274E: Lambda sensor error Nemst cable VKAT bank 1

Test pipes are on my car with tune. Cleared CEL and still comes back after a few days. Some days it won’t come on and the car feels night and day. Having troubles figuring out if I should replace my o2 senors or it could be something else.

[amrazM]

you should really replace all 4 sensors at the same time, they are not that expensive.

[DrFerry]

When you remove the primary cats - by installing test pipes or an X Pipe - the CEL has to be turned off by coding it out with a tune.

[ExoticM3]

DrFerry as stated in the description, I coded the CEL out with a tune by alpinemss.

[ExoticM3]

amrazM will most likely have to do this, just don’t want to replace them again if this happens again.

[dpaul]

Originally Posted by ExoticM3

2740: Lambda sensor heating control diagnostic VKAT bank 1

274E: Lambda sensor error Nemst cable VKAT bank 1

Test pipes are on my car with tune. Cleared CEL and still comes back after a few days. Some days it won’t come on and the car feels night and day. Having troubles figuring out if I should replace my o2 senors or it could be something else.

It could be the bank 1 pre-cat sensor or a cable/connector problem. If this problem occurred shortly after the test pipe installation, very possible whoever did it damaged the sensor or overtwisted the wires. No reason to replace all four sensors or even the two bank 1 sensors. Just the pre-cat sensor.

[ExoticM3]

dpaul yeah I had a feeling the person may have messed it up. No issue occurred for a 100 miles or so after it was installed and tuned. Thanks for the feedback

[RocketyMan]

Originally Posted by amrazM

you should really replace all 4 sensors at the same time, they are not that expensive.

There is absolutely no point to this. The post-cat O2s are used only to tell compliance of the primary cats...nothing else.

[HeavyArmZ]

I would switch sides for the primary sensors and see if the codes follows. That should verify your issue.

[amrazM]

Originally Posted by RocketyMan

There is absolutely no point to this. The post-cat O2s are used only to tell compliance of the primary cats...nothing else.

the post-cat sensors are narrow-band and thus exhibit a very sharp transition in voltage output around lambda =1 the voltage changes rapidly just above or just below. Meaning they don't accurate report small changes in AFR but very accurately report lambda =1 ("stoichiometric" regardless of fuel type). The pre-cat sensors, are wide-band which makes them useful for reporting minor difference in AFR around stoichiometric which is what you want for fine tuning the AFR. But as a necessary consequence, the pre-cat sensors exhibit relatively small voltage changes around lambda = 1. Meaning, they accurately report small changes in AFR but don't accurately report lambda = 1. So the DME uses the post-cat sensors as a standard to accurately calibrate the output of pre-cat sensors at lambda =1. If you remove the post-cat sensors, things eventually drift out of calibration and you have problems.

regardless tunes don't delete the rear o2's, they simply remove the ability for the DME to complete the cat monitor readiness which eliminates the CEL.

[DrFerry]

So there could also be something wrong with the tune then…

[RocketyMan]

Originally Posted by amrazM

the post-cat sensors are narrow-band and thus exhibit a very sharp transition in voltage output around lambda =1 the voltage changes rapidly just above or just below. Meaning they don't accurate report small changes in AFR but very accurately report lambda =1 ("stoichiometric" regardless of fuel type). The pre-cat sensors, are wide-band which makes them useful for reporting minor difference in AFR around stoichiometric which is what you want for fine tuning the AFR. But as a necessary consequence, the pre-cat sensors exhibit relatively small voltage changes around lambda = 1. Meaning, they accurately report small changes in AFR but don't accurately report lambda = 1. So the DME uses the post-cat sensors as a standard to accurately calibrate the output of pre-cat sensors at lambda =1. If you remove the post-cat sensors, things eventually drift out of calibration and you have problems.

regardless tunes don't delete the rear o2's, they simply remove the ability for the DME to complete the cat monitor readiness which eliminates the CEL.

This makes absolutely no sense.

These engines are speed density based, therefore the DME refers to a VE table. Primary O2 sensors are used as a "CLOSED LOOP" feedback for the targeted lambda (or AFR) tables. Post O2 sensors are not used for this.

The main purpose of the post O2 sensors are to determine COMPLIANCE of emissions. You do realize that any mixture post cat is supposed to be consumed by the reaction, right? In other words, the catalytic converter is an OXYGEN storage device, therefore, any mixture that runs through it(with a set of correct conditions) gets converted (or reaction to completion) through a properly operating catalytic converter. ScannerDanner talks a little bit about this. Review here:

Back to the OP, he clearly stated that "test pipes" are installed on his vehicle, thus, NO primary catalytic converters are on his vehicle making the post-cat O2 sensors non-functional for their purpose. Hence, the "tune" thus disabling the CEL for that logic monitor. His fault codes are not dealing with post-cat O2s--they are for primary O2s; the heating circuit and sensing for bank 1.

[amrazM]

Originally Posted by RocketyMan

This makes absolutely no sense.

These engines are speed density based, therefore the DME refers to a VE table. Primary O2 sensors are used as a "CLOSED LOOP" feedback for the targeted lambda (or AFR) tables. Post O2 sensors are not used for this.

The main purpose of the post O2 sensors are to determine COMPLIANCE of emissions. You do realize that any mixture post cat is supposed to be consumed by the reaction, right? In other words, the catalytic converter is an OXYGEN storage device, therefore, any mixture that runs through it(with a set of correct conditions) gets converted (or reaction to completion) through a properly operating catalytic converter. ScannerDanner talks a little bit about this. Review here:

nobody cares about scanner dave, im telling you from my own experience with this brand that a bad POST cat sensor causes issues in this car with long term fuel trims.

the whole point of my post is that a single O2 sensor code on this car thats already 10 years old would call for replacement of all 4 o2 sensors. they were installed at the same time.

[dpaul]

Originally Posted by RocketyMan

This makes absolutely no sense.

These engines are speed density based, therefore the DME refers to a VE table. Primary O2 sensors are used as a "CLOSED LOOP" feedback for the targeted lambda (or AFR) tables. Post O2 sensors are not used for this.

The main purpose of the post O2 sensors are to determine COMPLIANCE of emissions. You do realize that any mixture post cat is supposed to be consumed by the reaction, right? In other words, the catalytic converter is an OXYGEN storage device, therefore, any mixture that runs through it(with a set of correct conditions) gets converted (or reaction to completion) through a properly operating catalytic converter. ScannerDanner talks a little bit about this.

Back to the OP, he clearly stated that "test pipes" are installed on his vehicle, thus, NO primary catalytic converters are on his vehicle making the post-cat O2 sensors non-functional for their purpose. Hence, the "tune" thus disabling the CEL for that logic monitor. His fault codes are not dealing with post-cat O2s--they are for primary O2s; the heating circuit and sensing for bank 1.

amrazM may be correct about the importance of post-cat sensor input. I can confirm that his analysis is 100% correct in the case of the N54 engine with MSD81 DME i.e. input from post-cat sensors is used for calibrating pre-cat sensor range. It is reasonable to assume that BMW would employ a similar strategy in all product lines (but of course that's just a guess for me). Regardless. the post-cat sensors are not 'disabled' by most tunes; only OBDII test logic is disabled.