Mercedes-Benz W203 CDI: boost pressure too low and turbocharger faults
Mercedes-Benz W203 CDI goes into limp mode and the fault code says boost pressure is too low. What causes it?
The car limits power when boost pressure deviates from the permitted range. The cause is usually the boost pressure sensor, the turbocharger actuator or its linkage, the vacuum lines or a leaking charge pipe. The code alone does not name the part, so the fault is located by measuring.
Mercedes-Benz W203 CDI: what should be checked first on the turbocharger and its control?
Check the mobility of the turbocharger vanes and the actuator lever, the condition of the vacuum lines and, on an electrically controlled turbocharger, the wiring and the actuator motor. Also check the boost pressure sensor hose and the charge hoses and intercooler for leaks. The sensor type matters: there are several different sensors for the 200 CDI.
Mercedes-Benz W203 CDI: what causes a hissing noise on acceleration?
Usually air escapes from a cracked charge pipe or hose or from a detached connection. A leaking intercooler also causes a hissing noise and weak boost. Pipes age and crack, so check the whole charge path from the turbo to the intercooler.
Mercedes-Benz W203: is it normal for the MAP sensor to show about 1 bar at idle?
Yes. The sensor measures absolute pressure, so at idle the reading is close to atmospheric pressure. Boost pressure is added on top of it, so the reading rises only as boost builds.