Document about lack of power in A4, 2.5 TDI (Solution)

Audi A4, model years 1998 to 2001.
All models with the specified engine.


AFB/AKN V6 TDI engine.

Symptoms:
Lack of power, loud knocking noise after cold start or under partial load, engine running roughly, automatic transmission in emergency mode.

Causes:
Timing belt tensioner for the camshaft timing belt: difficult to turn, seized, or tensioner element defective. The timing belt will no longer be tensioned during operation.
This can cause the injection timing to shift. In extreme cases, as a result of this, an error code 0550 (start of injection, control difference) may be recorded in the engine control unit's fault memory. In vehicles with automatic transmissions, the transmission control unit then enters a limp-home mode.

Solution:
Remove the timing belt tensioner and check its smooth operation on the mounting bolt. Replace if necessary.
Note: The tensioning element is oil-damped and can only be adjusted slowly and with even force.
It needs to be compressed and should automatically extend again. A washer must be installed between the cylinder block and the tensioner.