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Old 06-08-2016, 06:24 PM   #1
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Got a CEL (check engine light) indicating a NOX sensor issue. Trip to MB dealer today found this; Per the technician, MB allows the technician to replace the SCR (selective catalytic reduction) part along with the two NOX sensors. According to the technician, MB has belief that in years '11, '12 and '13 the SCR isn't functioning according to design specs, due to buildup of particulate at a much greater rate than anticipated.That, in turn, triggers a NOX sensor failure. Meaning the designed life of the SCR, somewhere around 300K miles, isn't even coming close to that, resulting in pre-mature failure (filling up with particulate). The SCR, or in simple terms, catalytic converter, is not able to digest the particulate within design spec. That causes NOX sensor(s) to trigger the CEL. Also, the technician said MB is seeing this anomaly primarily in Sprinters 3500's, used by the RV and ambulance industry. MBs fix was to change to a different SCR manufacturer, to address these increased failures showing up in RV and ambulenceses. My discussion with the tech talked about the heavy loads beyond the average 3500s in use (non RV Ambulance units), and the fuel put through under load might be a cause. He more or less thought MB thought the same thing, because the increased failure occurance, beyond other 3500s not carrying the huge loads.

I'll have more on this when I pick it up.

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Old 06-09-2016, 06:22 PM   #2
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Update; Parts replaced NOX Sensor upstream of SCR catalytic converter, NOX sensor downstream of SCR, replace SCR, replace DEF injection nozzle. All replaced under technician recommendation, based on verbage on invoice "short test perform".
Interesting that all parts were in stock. Well the good is, CEL gone. Just hope MB engineered it better second time around.
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