Mercedes-Benz B200 CDI W246

The Getrag 7G-DCT (724.0) dual-clutch gearbox is the most common complaint across all W246 diesel models. The OM651's 300 Nm of torque puts significant stress on the dry clutch packs. Symptoms include jerking at low speeds, vibrations between 20-40 km/h, hesitation when pulling away, and clutch slippage when hot. Problems typically appear between 70,000-120,000 km, especially on cars used predominantly in city traffic. Over 70% of faulty gearboxes reportedly never had an oil change in the first 100,000 km. Mercedes considers the gearbox oil a lifetime fill, but specialists strongly recommend changing it every 60,000 km with MB 236.21 specification fluid. A clutch pack replacement costs approximately 900-1,400 with aftermarket parts, 1,500-2,000 with OEM. Mechatronics repair or replacement runs 1,200-3,000. A TCU software adaptation reset (100-200) can improve shift quality in early-stage symptoms. Manual gearbox variants are entirely unaffected.

The DPF on the OM651 requires the engine to reach full operating temperature and sustain approximately 2,000 rpm at 60+ km/h for regeneration. Cars used primarily for short urban trips accumulate soot beyond the point where passive regeneration is possible. Symptoms include the DPF warning light, reduced power, limp mode, and increased fuel consumption during failed regeneration attempts. A forced regeneration at a workshop costs 100-200. Professional off-car cleaning costs 300-500. Complete DPF replacement costs 1,200-2,000 including the catalytic converter section. The differential pressure sensor can also fail, preventing regeneration even on highway-driven cars (sensor replacement: 150-250). Regular motorway driving of at least 30 minutes per week significantly reduces the risk. Check the engine oil level before buying: if it is significantly above the maximum mark, diesel has been contaminating the oil from failed regenerations.

The OM651 uses a single-row (simplex) timing chain rather than a more durable duplex chain. This was acknowledged by Mercedes when the successor OM654 switched to a duplex design. The chain is located at the rear of the engine, making replacement labor-intensive. Symptoms begin as a distinctive metallic rattle for 1-5 seconds on cold start as the tensioner loses hydraulic pressure overnight. This typically starts between 120,000-180,000 km with proper oil changes, but can occur earlier with neglected maintenance. Mercedes has revised the tensioner multiple times. Parts for the full chain kit cost 200-400, but labor is substantial as the engine may need to be partially lifted. Total replacement cost is 1,000-1,800 at an independent specialist, 1,800-2,500 at a Mercedes dealer. Ignoring the rattle risks chain skip and catastrophic valve damage. Regular oil changes at 10,000-15,000 km intervals (rather than the factory 25,000 km) significantly extend chain life.

Like most modern diesels, the OM651 accumulates carbon deposits in the EGR valve and intake manifold over time. Symptoms include rough idling, hesitation under acceleration, black smoke, and increased fuel consumption. The EGR valve can stick open or closed. Cleaning the EGR valve and intake manifold costs 200-400 at a specialist. Full EGR valve replacement runs 350-900 including the part (150-400) and labor. The EGR cooler can also develop internal leaks, allowing coolant into the intake tract and causing white smoke on cold starts. EGR cooler replacement costs 400-800. Regular highway driving and quality diesel fuel help reduce buildup. Cleaning interval recommendation is every 80,000-120,000 km.

The OM651 fuel filter housing has coolant passages running through it and bolts to both the cylinder head and inlet manifold. Under boost pressure, the inlet manifold flexes, stressing the housing seals. This causes a slow coolant leak that can be difficult to pinpoint as it often drips internally rather than pooling visibly. Symptoms include gradually dropping coolant level with no obvious external leak, and sometimes a sweet smell from the engine bay. Mercedes released an updated housing design (part A6512003900). The replacement part costs 80-150, but the repair requires removing the EGR cooler and replacing its gasket as well, bringing total repair to 250-500 at an independent shop.

Early OM651 engines (2012-2013 production) used Delphi piezo injectors that proved sensitive to fuel quality. Symptoms include rough idle, misfiring, increased fuel consumption, and white/gray exhaust smoke. Mercedes issued a service campaign to replace these with updated solenoid-type injectors. Cars from mid-2013 onwards should already have been updated. A single remanufactured injector costs 200-350 with programming via Star diagnostic required. Replacing all four injectors costs 800-1,500 depending on whether remanufactured or new units are used. Check whether the injector service campaign was completed before purchasing.

Several W246 owners report the electronic parking brake becoming stuck or displaying a malfunction warning on the dashboard. The issue can be caused by a faulty actuator motor, corroded cables, or a software glitch in the control module. In some cases, holding the parking brake switch for 10+ seconds and restarting the engine resolves the problem. Lubricating the parking brake mechanisms with penetrating lubricant can also help. When the actuator itself needs replacement, costs run 300-700 including parts and labor. The issue is more common on cars that have had little use or have been stored for extended periods.