Mercedes-Benz W211 CDI rail pressure too low
What causes low rail pressure on a W211 CDI?
The most common causes are the quantity control valve next to the high-pressure pump and injector leak-back. The rail pressure sensor or an injector that lets pressure through can also cause the fault. The cause depends on the car and is told apart with a diagnostic tool.
What do fault codes P2047 and P2017 mean?
They relate to too low rail pressure. A common cause is the quantity control valve, whose replacement has fixed the fault. A valve replaced at the end of the rail did not fix it. The fault light can also point to the pressure sensor.
How do you tell the quantity control valve and injector leak-back apart?
With the Star diagnostic tool at a Mercedes-Benz specialist. If the pressure fluctuates by more than 20 bar at least three times during the test period, the quantity control valve must be replaced. Clearly larger fluctuation points to injector leak-back. The test results for the quantity control valve and the pressure regulator can also get mixed up, so it is worth checking both.
What else is checked for a rail pressure fault?
The output and pressure of the fuel transfer pump should be measured. An injector leak can prevent a cold start and cause smoke. Sometimes after repairing the injectors the injector support also has to be replaced.