TorqFix

W906 - OM646 (646.984)/985/986/989 engine - ancillary drive belt — MERCEDES-BENZ

W906 - OM646 (646.984)/985/986/989 engine - ancillary drive belt on Mercedes-Benz: 28 steps, engines 646.984, 646.985, 646.986, 646.989.

Workshop procedure for MERCEDES-BENZ — the exact step sequence and torque figures, straight from real workshop data.

28 steps 4 engine codes

🧭 Before you start

Fits: platform codes 209, CDI, |, 211, 213, 215, 309, 311, -4MATIC, 313, 315, 411, 413, 415, 511, 515

  • Timing position: the crankshaft or camshaft is set and locked during this job
  • Special tools named: locking pin

🔧 Engine codes this applies to

646.984646.985646.986646.989

📋 Procedure

Preparation and removal

  1. Turn the tensioner anti-clockwise
  2. Remove the tensioner locking pin
  3. Loosen the tensioner pulley bolt
  4. Move the tensioner to the slack position
  5. Remove the air-conditioning belt
646.984? Steps differ between engine variants — check this job against your exact car before you commit to it. Check my car — free →
  1. Remove the ancillary drive belt

Installation and checks

  1. Refit the ancillary drive belt
  2. Vehicles with additional air conditioning:
  3. All vehicles:
  4. Move the tensioner to the slack position
  5. Tighten the tensioner pulley bolt
  6. Lock the tensioner; use a locking pin
  7. All vehicles:
  8. Lower the vehicle
  9. Start the engine
  10. Check for correct operation

Other MERCEDES-BENZ procedures

Who makes these pages, and how

TorqFix was built by a mechanic — after a 2,700 km drive with five roadside repairs that no diagnostic tool could explain.

The figures on this page come from manufacturer workshop documentation and are shown as they are. The page is assembled automatically from that data — it is not written by an AI. The AI works in the chat, where it answers for your specific car. It writes nothing here.

Variants of the same model differ. Cross-check torque against the factory manual for your engine before final tightening.

Seen a figure that does not match your manual? Write to us — we correct it and note when. support@torqfix.com

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Workshop data on this page last updated 20 Sep 2026.