CEL with the following codes

Sparch · 01-29-2024, 07:39 PM

Need some experienced guidance

- DME active codes -
180001 - Catalytic converter: Efficiency too low.
21B28A - Info SGR48: Voltage at KL40: Undervoltage.

I installed the AA Catted DP back in beginning of December. I saw the above code (180001) but never got any CEL till today.

Now first time seeing the 21B28A undervoltage code today and CEL popped up.

Does anyone know what this new code is?

The only other mod I installed was MButtons from IAW and am wondering if that might be a factor? That was installed just before Christmas, so it has been in the car for a full month.

Trying to figure out also if I should remove both before taking the car to the dealership if I need them for resolution?

jasondff · 04-20-2026, 01:46 AM

Did the M1 M2 buttons cause this?

bimmabum · 04-21-2026, 06:58 PM

AA catted dp should not produce any cel, they have a no cel guarantee or free lifetime replacement if im not mistaken, maybe contact AA to replace that downpipe

tylers1027 · 04-21-2026, 07:06 PM

Same here - I have a AA downpipe and maybe about once a month or so I get the CEL for the same code. I just clear the code with the JB4. They said they'd replace it under warranty if I wanted; but I didn't want to pay for another install so I just clear the code for now.

01-29-2024, 07:39 PM	#1
Sparch Private 44 Rep 75 Posts Drives: M340i, 430i GC Join Date: Mar 2022 Location: Sunshine State iTrader: (0)	CEL with the following codes Need some experienced guidance - DME active codes - 180001 - Catalytic converter: Efficiency too low. 21B28A - Info SGR48: Voltage at KL40: Undervoltage. I installed the AA Catted DP back in beginning of December. I saw the above code (180001) but never got any CEL till today. Now first time seeing the 21B28A undervoltage code today and CEL popped up. Does anyone know what this new code is? The only other mod I installed was MButtons from IAW and am wondering if that might be a factor? That was installed just before Christmas, so it has been in the car for a full month. Trying to figure out also if I should remove both before taking the car to the dealership if I need them for resolution? Attached Images
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04-20-2026, 01:46 AM	#2
jasondff Registered 0 Rep 1 Posts Drives: 2023 BMW M340i XDrive Join Date: Apr 2026 Location: New York iTrader: (0)	Did the M1 M2 buttons cause this?
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04-21-2026, 06:58 PM	#3
bimmabum Soldier 161 Rep 575 Posts Drives: M340i 2023 Join Date: Dec 2023 Location: canada iTrader: (0)	AA catted dp should not produce any cel, they have a no cel guarantee or free lifetime replacement if im not mistaken, maybe contact AA to replace that downpipe
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04-21-2026, 07:06 PM	#4
tylers1027 First Lieutenant 236 Rep 324 Posts Drives: 2022 330I Join Date: Jan 2022 Location: Willoughby, Ohio iTrader: (1)	Same here - I have a AA downpipe and maybe about once a month or so I get the CEL for the same code. I just clear the code with the JB4. They said they'd replace it under warranty if I wanted; but I didn't want to pay for another install so I just clear the code for now.
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