Bad NOX Post-Catalytic Converter Sensor

Xerix · 03-16-2023, 03:03 PM

Hey Everyone,

Im getting a bunch of codes for my post catalytic converter NOX sensor... The $1,000 one :-(

ISTA says that the computer has blocked it from the system and I have codes
4744: DDE: Nitrogen oxide sensor down stream of SCR catalytic converter, line disconnection short circuit to B+
4749: DDE: Nitrogen oxide sensor down stream of SCR catalytic converter, line disconnection short circuit to ground

So I tried the troubleshooting through ISTA, and it was showing a PPM count of -50, blocked. The upstream sensor was working fine ranging from about 90ppm up to 400+ while driving. The Post Cat NOX sensor never reports anything at all even after a code reset.

I also see other non-active codes present via "Car Scanner" mobile app for:
P229E: NOX Sensor 2, Bank 1 circuit malfunction
P229F: NOX Sensor 2, Bank 1 circuit range/performance

Im 99% sure the NOX sensor Post Cat is dead. Would anyone else venture an idea for me to double check something before I spend $1000 on the sensor? I called a couple scrap yards, and they dont have any BMW diesels available, so thats not an option unfortunately.

Thanks for any help.

Xerix · 03-16-2023, 09:55 PM

In addition to my original post, I have performed the tests described at https://bimmerprofs.com/electric-con...x-sensor-2eae/

All of which seems to pass their requirements for a working harness and sensor. BUT, Fault Code 4744 I don't think can be tested with those procedures as it describes a load drop fault. Trying to read up on how test that out now

Sensor Pins
Pin 3 - 4 = 120.8 ohms
Pin 2 - 3 = 14.73 K ohms
Pin 2 - 4 = 14.73 K ohms
Pin 1 - 2 = 136 K ohms

Wire Harness Pins With Ignition On
Pin 1 - 2 = Test Light works (!2V)
Pin 2 - GND Exhaust = 2.5 ohms

Wire Harness Pins with Battery Disconnected
Pin 3 - 4 = 118 ohms
Pin 3 - Exhaust Bung = 7.14 K ohms
Pin 4 - Exhaust Bung = 7.16 K ohms

Xerix · 03-16-2023, 10:09 PM

I found this thread on the exact issue: https://www.e90post.com/forums/showt...1#post29942971

I will post my replacement results once done tomorrow.

Xerix · 03-17-2023, 01:05 PM

Replaced sensor with a new one. All is good now.

03-16-2023, 03:03 PM	#1
Xerix Private First Class 30 Rep 119 Posts Drives: 2010 335d Join Date: Jun 2014 Location: Toronto iTrader: (0)	Bad NOX Post-Catalytic Converter Sensor Hey Everyone, Im getting a bunch of codes for my post catalytic converter NOX sensor... The $1,000 one :-( ISTA says that the computer has blocked it from the system and I have codes 4744: DDE: Nitrogen oxide sensor down stream of SCR catalytic converter, line disconnection short circuit to B+ 4749: DDE: Nitrogen oxide sensor down stream of SCR catalytic converter, line disconnection short circuit to ground So I tried the troubleshooting through ISTA, and it was showing a PPM count of -50, blocked. The upstream sensor was working fine ranging from about 90ppm up to 400+ while driving. The Post Cat NOX sensor never reports anything at all even after a code reset. I also see other non-active codes present via "Car Scanner" mobile app for: P229E: NOX Sensor 2, Bank 1 circuit malfunction P229F: NOX Sensor 2, Bank 1 circuit range/performance Im 99% sure the NOX sensor Post Cat is dead. Would anyone else venture an idea for me to double check something before I spend $1000 on the sensor? I called a couple scrap yards, and they dont have any BMW diesels available, so thats not an option unfortunately. Thanks for any help.
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03-16-2023, 09:55 PM	#2
Xerix Private First Class 30 Rep 119 Posts Drives: 2010 335d Join Date: Jun 2014 Location: Toronto iTrader: (0)	In addition to my original post, I have performed the tests described at https://bimmerprofs.com/electric-con...x-sensor-2eae/ All of which seems to pass their requirements for a working harness and sensor. BUT, Fault Code 4744 I don't think can be tested with those procedures as it describes a load drop fault. Trying to read up on how test that out now Sensor Pins Pin 3 - 4 = 120.8 ohms Pin 2 - 3 = 14.73 K ohms Pin 2 - 4 = 14.73 K ohms Pin 1 - 2 = 136 K ohms Wire Harness Pins With Ignition On Pin 1 - 2 = Test Light works (!2V) Pin 2 - GND Exhaust = 2.5 ohms Wire Harness Pins with Battery Disconnected Pin 3 - 4 = 118 ohms Pin 3 - Exhaust Bung = 7.14 K ohms Pin 4 - Exhaust Bung = 7.16 K ohms
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03-16-2023, 10:09 PM	#3
Xerix Private First Class 30 Rep 119 Posts Drives: 2010 335d Join Date: Jun 2014 Location: Toronto iTrader: (0)	I found this thread on the exact issue: https://www.e90post.com/forums/showt...1#post29942971 I will post my replacement results once done tomorrow.
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03-17-2023, 01:05 PM	#4
Xerix Private First Class 30 Rep 119 Posts Drives: 2010 335d Join Date: Jun 2014 Location: Toronto iTrader: (0)	Replaced sensor with a new one. All is good now.
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