Mercedes-Benz W203 CDI: revs limited to about 3000 rpm
Mercedes-Benz W203 CDI: why does it not rev past 3000 rpm and the warning light is on?
Revs limited to about 3000 is the engine's limp mode: the control unit limits power when some measurement or the boost pressure does not match. The fault often clears by switching the car off and on, but the cause must be found. It is located from the fault codes and sensor readings.
Mercedes-Benz W203 CDI: which sensors and parts cause the rev limit?
The most common is the mass air flow sensor (it measures the amount of air the engine draws in), whose fault can show only when warm and not always in a fault test. Others are the particulate filter differential pressure sensor and its hoses, and the EGR valve (exhaust gas recirculation) and its vacuum hose.
Mercedes-Benz W203 CDI: can a charge hose or intercooler limit the revs?
Yes. A crack in the charge pipe, a detached charge hose, a hole or a torn end tank in the intercooler, and a chafed vacuum hose cause a boost pressure leak and loss of power. The leak does not necessarily show at idle, so the hoses and the intercooler are worth checking.
Mercedes-Benz W203 CDI: how do you find the cause of the rev limit?
You need the fault codes and the mass air flow and boost pressure readings: an ordinary OBD reader does not show everything, so a Star-type diagnostic tool helps. Without one, first inspect the hoses and connections visually and then look for the fault one part at a time.