The search for clean Diesel began for Daimler in Model Year 2006 when Bluetec was introduced into Mercedes-Benz best selling sedan the E-Class. Bluetec was designed to scrub the exhaust of harmful NOX emissions created by the lean air fuel ratios of the new Mercedes-Benz diesel engines.

Some Background

The following article:
Controlling Diesel Emissions
explains the details of diesel emission control with specific information about the urea injection technique used in MB vehicles to reduce nitrogen oxides in the exhaust. Urea solution, also known as Diesel Exhaust Fluid or DEF, is stored in a separate heated tank in the vehicle. (This is also referred to as the AdBlue® tank.) DEF injection into the exhaust stream is controlled by the ECM, which monitors various engine operation parameters and the exhaust mixture. Use of the urea system allows the diesel engine to run closer to optimum fuel mixture.

By 2010 the first Sprinter with Bluetec was released. Along with a cascade of problematic components and repair procedures that plagued the automotive repair industry. While Bluetec passenger vehicles often experience similar no-start characteristics, commercial vehicles such as Sprinter and Frieghtliner with Bluetec Diesels are most commonly used as work vehicles or Luxury Van’s.

Servicing these vehicles became more frequent as many of them came out of manufacturer warranty due to higher mileage versus passenger vehicles such as E-Class and GL-Class. Many of the repairs fell on the independent aftermarket once vehicles fell out of warranty. Without a proper understanding of the Bluetec system, often times vehicle fault codes were misguided and improperly diagnosed, with several unnecessary components replaced.  Several new software updates were released by the manufacturer with little to no detail on what improvements would occur. Vehicle owners that neglected to continue to service and top off the Adblue (Diesel Exhaust Fluid) (DEF) would find themselves with Zero Starts remaining once the Adblue tank ran dry, causing a cascade of problems such as crystallization of the injection valve (Metering valve) as well as other DEF related failures.


“On March 9, 2021, a settlement was approved between Daimler AG and Mercedes-Benz USA, LLC (“MBUSA”) and the United States Department of Justice (DOJ), the Environmental Protection Agency (EPA), the California Air Resources Board (CARB), and the California Attorney General’s Office (CA AG), regarding the emission control system in these vehicle. As part of this settlement, they are offering a modification to your emission control system. The emission modification for Mercedes-Benz vehicles has been approved by the EPA and CARB, and is now ready for installation. An authorized Mercedes-Benz dealer will install the modification at no cost to the vehicle owner.” An “Approved Emission Modification” or “AEM” is an emission control system modification approved by the U.S. Environmental Protection Agency and the California Air Resources Board that must be installed in Subject Vehicles.

If you or your customer owns a diesel Mercedes model dating from 2009 to 2020, a letter will be received from MB USA which starts with the paragraph above.

The letter continues at length, explaining the modifications and “updates” that Mercedes is forced to make based on the settlement with US and state authorities: The engine control module (ECM) and its software, NOx sensors, oxygen sensors are removed (some models), and the selective catalytic reduction (SCR) catalyst. The repairs to be made under this settlement will take approximately 2.5 – 6 hours and are free of charge to the vehicle owner. The Mercedes diesel owner is assured that there will be no adverse effect due to these modifications to the efficiency or drivability of the vehicle and no impact on the “vehicle’s ability to comply with … inspection and maintenance.” Once the Emission Modification is performed, certain components will have an extended warranty for the greater of 4 years/48,000 miles from the date of installation of the Emission Modification or 10 years/120,000 miles from the initial sale date of the vehicle. Verification of these modifications can be identified by an approved emissions modification label under the hood near the hood latch.

Part of the settlement cost is to be borne by Bosch, the supplier of electronic components to the auto manufacturer.

As a result of this settlement, if you are an independent MB repair shop owner, you need to inform vehicle owners of recent diesel models (from 2009 to 2020) to check the settlement web site: Or call 1-833-841-9363.

The owner needs to provide the vehicle VIN to see if the terms of this settlement apply to them. The settlement includes nearly all Sprinter and Freightliner diesel Bluetec models, as well as E-Class, ML, GL, GLK and all Bluetec diesel vehicles.

The malfunctions that have plagued these MB diesel models range widely, so it is difficult to pinpoint exactly what defect you should expect to see when diagnosing a vehicle. One example iSCAN customers dealt with was NOx sensor failure. Requiring not only component replacement, but also advanced Software Calibration Number (SCN) performed using an iSCAN diagnostic tool.

What the letter from MB USA does not explain is the reason that these modifications and component replacements are now required. Investigation by researchers uncovered a pattern  that Bosch and Mercedes built into the electronics in diesel vehicles. The research was started because many diesel owners began to complain of similar malfunctions in their vehicles. Eventually, these owners banded together to form a class-action suit vs. Mercedes and eventually that led to the CARB-EPA-DOJ action and settlement.

In particular, Bosch and MB apparently programmed the ECM to register and report differently while being tested (as in state-mandated emissions testing) vs during normal operation. This is considered a violation of the EPA certification of conformity to US law.

Here are some DTC that are related to catalyst and DEF system failures:

P15B700 – One or more signals sent from control unit SCR via CAN bus is implausible.

P300662 – The AdBlue® system has a malfunction.

P300660 – The AdBlue® fill level is low. The fluid level is too low.
P16CF00 – AdBlue Warning Message “Stage 2” The number of possible engine starts is limited due to malfunction in the AdBlue system.
P19DE00– The emission limit for NOx concentration has been exceeded (exhaust gas recirculation was shut off)

P13DF00 – The AdBlue® system has a malfunction.

P300A62 – The NOx sensor  1(cylinder bank 1) has a malfunction.

P204B08 – The AdBlue® pressure sensor has a malfunction. There is a signal fault or the message is faulty.
P204B87 – The AdBlue® pressure sensor has a malfunction. The message is missing.
P208A00 – The output for the AdBlue® delivery pump has an electrical fault or an open circuit. _
P20EA9A – The output for relay ”AdBlue® supply” has a malfunction (shutoff too early). The operating conditions for the component or the system are not satisfied.
U0401E5 – Implausible data were received from control unit ”combustion engine”.
U05A308 – Communication with the component ”A103/1 (AdBlue® tank module)” has a malfunction. There is a signal fault or the message is faulty.
U05A387 – Communication with the component ”A103/1 (AdBlue® tank module)” has a malfunction. The message is missing.

The Mercedes letter to owners, mentioned earlier, makes the following point with regard to the “improved” modified diesel vehicles: “The emission modification may change the frequency with which you need to refill your DEF (also known as AdBlue®) tank.” This is caused by the fact that under the previous emission protocols, the ECM did not call for much urea injection – not enough to actually reduce oxides of nitrogen as much as they were saying they could. As a result of the new software, your DEF consumption may increase.

While the independent aftermarket repair has already begun to deal with these bluetec vehicles, we at iSCAN would encourage repair facilities to research their own customers vehicles to ensure any repair requests are performed by an authorized dealer for repairs that are covered under this extended warranty period.

You can find more information on how to file a claim here >