Mercedes CDI Diesel and Sprinter SCR Problems
I recently observed a factory Mercedes webinar for the complex problem of diagnosing and repairing Mercedes SCR systems for diesel cars and trucks and Mercedes Sprinter vans. We put this knowledge to use today for repairing a 2010 Sprinter van with an SCR problem.
SCR stands for Selective Catalytic Reduction and the vehicles that have it are usually labeled or badged ”BlueTec” It is the environmentally-friendly diesel technology from Mercedes Benz used to reduce emission levels. BlueTec uses Urea or diesel emissions fluid injection into exhaust gas stream in specially designed chambers in the exhaust to reduce emissions, especially NOx (oxides of Nitrogen).
The factory scan tool can be misleading and it is common for technicians to misdiagnose the system and change expensive parts needlessly. This fairly new technology uses the Mercedes SD connect to connect directly to the high-speed chassis CAN network of the vehicle. This allows monitoring of the raw sensor data and non-calculated information for precise diagnosis. The factory Xentry scanner cannot display and process this information the way this specially designed package can. On this vehicle we discovered a slight difference in the NOx sensor readings between the front and rear sensor and this led to diagnosing a faulty front NOx sensor. These sensors are around $600 at the time of this article but this is still way cheaper than if it was misdiagnosed as an SCR failure (currently $3700).