Despite its robust design, the OM646 has several well-documented weaknesses. A workshop manual is invaluable here, providing the diagnostic trees, torque specifications, and step-by-step procedures to correctly identify and rectify these issues.
Turbocharged with Intercooler (VNT/VTG technology). 2. Essential Torque Specifications Mercedes Workshop Manual Om646 Engine
The OM646 uses swirl flaps inside the intake manifold. Over time, oil blow-by mixed with EGR soot creates a thick sludge that jams these flaps, stripping the plastic linkage rod or burning out the servo motor. Remediation requires replacing or thoroughly cleaning the intake manifold assembly. Despite its robust design, the OM646 has several