Condemning a BMW SCR catalyst?

Brandon Technician Medina, Minnesota Posted   Latest   Edited  
Question
Emissions
Driveability
2011 BMW X5 xDrive35d 3.0L (M57T2D30) 6-spd (GA6HP26Z)—5UXZW0C57BL660002
4D16 - Scr System Efficiency

We sold a 2011 X5 35d with the M57 to a customer that lives a few hours from us. It had a 4D16 - SCR system efficiency code found at her local Euro shop, they directed her to the dealership. She brought it back to us, that code is nowhere to be found, but I had an SCR active tank heater code instead. I verified the tank heater element was faulty and sent it to BMW to get replaced under the extended warranty, put some miles on it and confirmed the SCR monitor passed. I did another system test with ISTA before we delivered it back to the customer and it now has the 4D16 stored, but not current (nor historic). I dig into it, inspect the DEF metering valve and mixer per SI B18 02 17 and run the SCR efficiency test plan in ISTA, no DEF build up in the system, dispenses DEF within the 25-35g spec, NOx sensors are clean. I ran the entire test plan and the SCR catalyst passed, NOx sensors passed, EGT passed. I do not want to give back the vehicle until it's fixed.

BEFORE:

diag​.​net/file/f6bxzsqw2…

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1. The NOx sensors are the older versions that are prone to magnesium poisoning. I do not have any NOx codes whatsoever. Am I reading SI B01 10 17 correctly in that they will replace them under the extended warranty because they are the old P/N, but not setting NOx codes?

2. Guys that have replaced the SCR cat or run the test plan - what known good numbers should I be seeing after the test is run? I attached the results.

UPDATE: We sent the vehicle off to BMW with the hope they would replace the NOx sensors under extended warranty with just the 4D16 code present, which they did. I re-ran the SCR efficiency test plan, we jumped from about 74% to 86% NOx conversion and the sensors are reading much more consistent. I also did a forced regen before sending it on ISTA's recommendation with no appreciable change. The regen prior to the forced one was approx. 250km prior.

AFTER

diag​.​net/file/f7ena734a… diag​.​net/file/f3915qnmt…

diag​.​net/file/f5uxawuaa…

diag​.​net/file/f6k20tv2v…

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diag​.​net/file/f7dzy5bif…

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Matthew Mobile Technician
Bartlett, Illinois
Matthew
 

I have never worked on BMW, but there is an easy way I test NOx sensors. Disable the DEF doser and drive the vehicle looking at data. After the exhaust is warmed up and DEF consumed from SCR your NOx sensors should match pretty close to each other.

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Brandon Technician
Medina, Minnesota
Brandon
 

The ISTA test plan accomplishes that on the lift, the entire test takes about 50 minutes to run autonomously. They did match each other during the catalyst prep part of the test.

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Matthew Mobile Technician
Bartlett, Illinois
Matthew
 

Okay, Cummins does something similar in their SCR test.

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Stuart Owner/Technician
Prestonpans, United Kingdom
Stuart
 

Can you tell me what the acronym DEF is? Diesel Emission Fluid ?

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Matthew Mobile Technician
Bartlett, Illinois
Matthew
 

Diesel Exhaust Fluid

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Stuart Owner/Technician
Prestonpans, United Kingdom
Stuart
 

Thanks was just wanting to make sure we were on The same wavelength 👍

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Brandon Technician
Medina, Minnesota
Brandon
 

Diesel Exhaust Fluid, Diesel Emissions Fluid, AdBlue, Urea Mixture, it's all the same.

0 Ð Bounty Awarded
Stuart Owner/Technician
Prestonpans, United Kingdom
Stuart
 

Thanks was just wanting to make sure we were on The same wavelength 👍

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Nelson Manager
Huntington Beach, California
Nelson
   

Maybe i'm reading the graph wrong (it is late) but your 2nd graph shows the AFTER SCR NOx sensor reading higher than your BEFORE SCR NOx sensor. This should never happen. Usually a faulty dosing valve leaking raw urea into the exhaust system will do this (doubt it in this situation) or faulty NOx sensors. I wouldn't give that vehicle back to the customer without at least replacing BOTH NOx…

+2 Ð Bounty Awarded
Brandon Technician
Medina, Minnesota
Brandon
 

I had the same thought until I looked closer, the lowest wavy green line is the pre-cat NOx, the top red flat line is the post-cat NOx. The blue line is the NOx ratio of before and after like a math channel. I agree with not giving the vehicle back until it has at least 2 new NOx sensors, the big question is will BMW's extended warranty cover them IF there aren't any NOx fault codes, just SCR…

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Brandon Technician
Medina, Minnesota
Brandon
 

I updated the original post with new information.

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Nelson Manager
Huntington Beach, California
Nelson
 

Your readings look a lot better. Your long term adaptation factor is basically on the money. What is your particulate filter back pressure reading at idle and with the engine loaded up with the brakes applied? I have a feeling you fixed this vehicle. Knock on wood.

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Brandon Technician
Medina, Minnesota
Brandon
 

Yes, everything looks much better than before. I'm fairly confident they reset long term adaptation factor at BMW as part of the NOx sensor replacement, it's still at 1.00 in the DDE and I expect it to adjust at some point. Backpressure at idle fluctuates between -5.0 and -8.0mBar. Loaded is 12.0mBar. I did see in the DDE a regen was requested even though the engine has only been run 41…

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Nelson Manager
Huntington Beach, California
Nelson
 

Hey, Sorry for the late response. Not sure why they did, that DPF back pressure is fine.

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