EGR clogging and soot buildup
Often reportedIn the OM656 engine, soot buildup can occur in the EGR system and intake passages, especially with city or short-distance driving; this can lead to power loss and rough idle.
Engine Bay
The most frequently mentioned issue when buying a used Mercedes-Benz GLC 400d 4MATIC 9G-TRONIC 2020: EGR clogging and soot buildup. Additionally, high oil consumption is also commonly reported.
Be cautious
Most reported issue: EGR clogging and soot buildup. Service history and a test drive matter.
Listed from most frequently reported, each with its source.
In the OM656 engine, soot buildup can occur in the EGR system and intake passages, especially with city or short-distance driving; this can lead to power loss and rough idle.
Engine Bay
Numerous technical reports and user accounts indicate above-average oil consumption cases in the OM656 engine, which may require more frequent oil top-ups. If excessive oil consumption is not monitored, it can lead to lubrication issues and damage to the turbocharger or other mechanical components.
Engine Internal
In some OM656 variants, the Camtronic variable valve timing system may fail due to wear in actuators/solenoids or control components; this can lead to timing errors, rough idle, and reduced performance.
Engine Internal
The OM656 engine uses an advanced common rail system with a CP4 high-pressure pump and piezo injectors. The system is sensitive to fuel quality: water, contaminants, or poor-quality diesel can cause premature wear.
Fuel System
The turbocharger in the OM656 engine has been reported to fail due to insufficient lubrication, oil contamination, or thermal stress.
Turbo
Same trim, different year
We only publish claims we can verify. Cards come from European fault records and owner reports matched to this vehicle on brand, fuel, engine and generation.