Mercedes Workshop Manual Om646 Engine ~upd~ -

Injector & common-rail service

Precise Torque Specifications: The OM646 uses aluminum cylinder heads and "torque-to-yield" (stretch) head bolts. Over-tightening strips threads; under-tightening blows head gaskets. The manual lists exact Nm values and tightening sequences (often multi-stage angles, e.g., 40 Nm + 90° + 90°).
Timing Chain Procedures: The OM646 uses a duplex timing chain located at the rear of the engine. Replacing it requires special locking tools (e.g., pin 602 589 00 63 00) and precise crank/cam alignment. The manual provides the step-by-step ritual.
Injector Learn-In (Coding): If you replace a fuel injector, you cannot just "plug and play." The ECM needs the new injector’s individual 6-digit code (QR code). The manual explains how to use SDS (Star Diagnosis System) to perform this critical learn-in procedure.
Oil Change Realities: The OM646 is sensitive to oil specification. It requires MB 229.31 or 229.51 (low-ash, low-SAPS) to protect the DPF (Diesel Particulate Filter). The workshop manual lists approved viscosities (usually 5W-30 or 5W-40) and exact capacities (e.g., 6.5 liters for the oil pan with filter).