Mercedes EGR Valve Test

The EGR valve on this Mercedes MBE 900 diesel engine was under suspicion so we hooked up the software and went into the test mode. The valve can be moved to any desired position using the software which indicates if the EGR is faulty or not. In the video the valve moves correctly when manipulated by us.

It's controlled by an electric motor that I have seen fail on occasion. Usually an EGR valve code will come up once the valve moves in the wrong direction. If you are unfamiliar what this valve does I will explain it's purpose. EGR cooled exhaust was one of the first designs in the engineering department by factory engineers to combat the levels of Nitrogen Oxide or NOx.

By cooling the exhaust before it enters the intake system the NOx is reduced with lower exhaust temperatures and less oxygen levels. The disadvantage of this process is soot levels are increased with cooler exhaust levels in the combustion chamber. The DPF filter takes care of this down the line as long as the engine is worked hard and there are no mechanical issues like extra fuel or oil getting into the combustion chamber.

The onboard computer controls the open and close routine of the EGR Valve. Up to 50% of the exhaust is routed into the engine intake according to the performance setting in the software. Different loads and speeds dictate the EGR settings. When the computer commands the valve to open to a certain percentage and it does not an engine code pops up. Poor engine performance will be the first sign there is a problem.

Without the engine software your hopes are slim to none figuring out the problem. Codes are explained very well and most times it will lead you down the right path. That's it, emissions are here to stay and EGR valves are essential to control NOx.