Starting authorization and fuel diagnosis
First separate no-crank from crank/no-start. No-crank requires testing the 12-volt system, start authorization, starter control and relevant interlocks. Crank/no-start requires checking engine speed input, fuel pressure, spark or injection command, and immobilizer status. Compare requested and measured fuel-rail pressure during the failure rather than guessing at the pump. Hot-soak and cold-start failures may follow different diagnostic paths.
Repair decisions and verification
Verify repeatable starts under the conditions that originally produced the fault and check for stored or pending faults.
Vehicle context: C 250, 2013. Chassis: C-Class W204 Sedan. The same warning may require a different diagnostic path on another engine or year.
Symptoms and customer complaints
MIL with P0191; technician could not locate the fuel-rail pressure sensor because available images did not match the engine.
MIL and lack of power on hard acceleration with P0002-77.
Information request for the high-pressure-fuel-pump replacement procedure; no vehicle fault stated.
MIL-only fuel-rail-pressure-sensor range/performance concern.
Recorded trouble codes: P0191, P0002-77. A stored code points to a monitored condition, not automatically to a failed component.
Diagnostic approach
The researched cases used checks including Monitor fuel-rail-pressure PID; Hard-acceleration verification after HPFP replacement. A technician must interpret the results in the context of the actual vehicle.
The recorded case findings included Exactly 75 psi; Engine has plenty of power; problem resolved. These findings are examples, not assumptions to apply to every Mercedes-Benz.
Documented causes in the source cases included Failed high-pressure fuel pump. Similar symptoms can result from other faults, so testing is needed before repair.
Reported successful case repairs included Replace high-pressure fuel pump. These are external research outcomes, not work claimed by our shop.
If you are experiencing similar symptoms, call Mich’s Foreign Cars in Hickory at 828-324-6012 with the vehicle year, engine, warning message and the conditions under which the problem occurs.