Failure mode - Mercedes-Benz 2.1L Twin-Turbo Diesel (Sprinter 2014-2018)

Fuel system: high-pressure pump and piezo injectors

Reliability tier: aggregated - verify before ordering, see /disclosure/

Symptoms

hard start / long crank, worse cold
rail-pressure DTCs, cylinder-balance complaints
power loss under load

Compare with the other causes of the same sign on this engine: hard start, long crank or no-start · loss of power, limp mode or derate (4 causes)

Root cause

Bosch common-rail with piezo injectors and a two-part high-pressure pump on the bi-turbo OM651. No single defect is documented in the pulled complaints (engine attribution mixed) - this stays a diagnosis-branch record; the hardware is card-backed so buyers can price the outcomes.

Diagnosis

log rail pressure during cranking - supply vs high-pressure control
cylinder balance / return-flow test where supported
filters and water separator first on fleet units

Fixes

diagnosis-driven repair: filters, injectors or high-pressure pump per findings ()

fuel-filter - more than one option: OM651 Fuel Filter (651-090-31-52), OM651 Fuel Water Separator (651-090-29-52)
injector - more than one option: OM651 Piezo Injector (651-070-30-87), OM651 Piezo Injector, exchange (651-070-29-87-64)
injection-pump - more than one option: OM651 High-Pressure Pump (651-070-26-01, current), OM651 High-Pressure Pump, second chain (651-070-28-01-64, current)

Prevalence

occasional