Mercedes A Klasse Hybrid EGR Valve Issue

I encountered a similar predicament with my Mercedes C Klasse, although it's not a hybrid. The symptoms you describe reduced power, check engine light, rough running certainly point toward a potential EGR valve issue. The hissing sound you mentioned could indicate a significant vacuum leak in the EGR system itself, possibly at a gasket or hose connection. Before condemning the valve outright, I suggest a thorough inspection of all vacuum lines associated with the EGR system. A cracked or disconnected hose can mimic the symptoms of a faulty valve. Furthermore, consider the possibility of carbon buildup within the EGR valve or its passages. Excessive carbon deposits can impede the valve's proper function, leading to similar symptoms. Has the vehicle had its emissions system checked recently?

You mentioned checking for carbon buildup. Is there a recommended procedure for inspecting and cleaning the EGR valve on this particular hybrid engine? I am hesitant to disassemble components without proper guidance, particularly given the intricate nature of the hybrid system. Also, regarding the vacuum lines, are there specific areas prone to failure that I should prioritize during my inspection? I want to ensure I'm addressing the most likely points of failure before considering a full automotive repair.

While a DIY cleaning attempt might seem appealing, given the electronic complexity of modern EGR valves and the potential for damaging sensitive components, I would recommend against attempting a cleaning without the proper tools and diagnostic equipment. The vacuum lines on these models are fairly robust, but pay close attention to any connections near the exhaust manifold, as heat cycling can accelerate degradation. The hissing sound truly suggests a leak, and pinpointing its source is crucial. Given the symptoms, the potential impact on vehicle emissions, and the potential for further complications, I strongly suggest consulting with a qualified automotive repair technician who specializes in Mercedes vehicles and, ideally, has experience with hybrid systems. A proper diagnostic procedure will be more cost-effective than replacing components based on speculation.

I appreciate your expertise. I've taken your advice and scheduled an appointment with a trusted mechanic specializing in Mercedes vehicles. Indeed, the diagnosis confirmed a defective EGR valve. The total repair cost, including parts and labor, came to 355€. Replacing the valve resolved all the issues – the engine now runs smoothly, the check engine light is off, and the hissing sound is gone. Thank you again for your invaluable guidance; it saved me considerable time and potential misdiagnoses.