The W210 E300 Turbodiesel with OM606 engine is mechanically robust but plagued by automatic transmission issues and biodiesel-related fuel system failures. The engine itself is nearly bulletproof when maintained, but ancillary systems and Mercedes-typical electrical gremlins require attention.
722.6 Automatic Transmission Failure (Conductor Plate & Valve Body)
Common · high severityTypical onset: 120,000-180,000 mi
Symptoms: Harsh or delayed shifts, especially 2-3 and 3-4, Limp mode activation, stuck in second gear, Erratic shifting when cold, improves when warm, Check engine light with transmission-related codes (P0715, P0735)
Fix: Replace conductor plate (13-pin connector inside transmission) and often valve body while transmission is dropped. Requires pan removal, fluid flush, and adaptation reset. 8-12 hours labor depending on whether valve body needs replacement or rebuild.
Estimated cost: $1,800-3,500
Biodiesel Fuel System Destruction (Injectors, Lift Pump, IP Seals)
Common · high severitySymptoms: Hard starting or extended cranking, especially cold, Black smoke, rough idle, loss of power under load, Fuel in oil (dilution from leaking injector seals), Air in fuel system, repeated need to bleed lines
Fix: Biodiesel and low-sulfur diesel dissolve old rubber seals in Bosch mechanical injection pump and injectors. Complete injector replacement with upgraded seals, injection pump reseal kit, and new lift pump. Injectors alone are 6-8 hours; full IP overhaul adds another 8-12 hours if done on-car. Many owners switch to Monark or rebuilt injectors with Viton seals.
Estimated cost: $2,500-5,000
Transmission Oil Cooler Line & Radiator Leaks
Common · medium severityTypical onset: 100,000-150,000 mi
Symptoms: Transmission fluid puddles under engine bay, often passenger side, Low transmission fluid warnings, slipping when hot, Pink/red fluid mixing with coolant in overflow tank (internal cooler failure)
Fix: Steel cooler lines rust through where they route near subframe. External line replacement is 3-4 hours. If internal radiator cooler fails, requires radiator replacement plus complete transmission fluid flush to remove coolant contamination (catastrophic if not caught early). 6-8 hours total with flush.
Estimated cost: $800-2,200
Front Suspension球头 & Thrust Arm Bushings
Common · medium severityTypical onset: 80,000-120,000 mi
Symptoms: Clunking over bumps, especially during turns, Wandering steering, poor highway tracking, Uneven inner tire wear, Vibration felt through steering wheel at 40-60 mph
Fix: W210 thrust arms (lower control arms) use hydraulic bushings that fail and cause geometry issues. Ball joints separate or develop play. Recommend replacing thrust arms as assemblies with Lemforder or Meyle HD parts. 4-6 hours for full front end refresh including alignment.
Estimated cost: $1,200-1,800
Engine Wiring Harness Biodegradation
Occasional · high severityTypical onset: 150,000+ mi or 15+ years age
Symptoms: Multiple intermittent electrical faults (MAF, coolant temp, glow plugs), Check engine light with implausible sensor codes, Rodent damage accelerates failure, brittle insulation crumbles to touch, Engine runs rough or won't start despite good mechanical condition
Fix: Mercedes used soy-based insulation pre-2005 that biodegrades. Requires complete engine harness replacement. 12-16 hours labor for proper installation with loom routing and connector sealing. Aftermarket harnesses available but quality varies; OE Mercedes harness is $800-1,200 in parts alone.
Estimated cost: $2,000-3,200
Vacuum System Leaks (EGR, Brake Booster, Turbo Actuator)
Common · low severityTypical onset: 100,000-140,000 mi
Symptoms: Hard brake pedal, reduced power assist, Turbo underboost or overboost codes, limp mode, Hissing noise near firewall or intake manifold, Rough idle, EGR system faults
Fix: Vacuum pump driven off camshaft; lines and check valves fail over time. Most common culprits are brake booster line at firewall (2 hours), turbo wastegate actuator diaphragm (3 hours), and EGR valve vacuum solenoid (1.5 hours). Smoke test to find leaks recommended.
Estimated cost: $400-1,200
Buy if you wrench yourself and the transmission shifts perfectly — the OM606 is legendary, but the 722.6 auto and biodiesel fuel issues will bankrupt you at a dealer.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.