Common Mercedes OM646 Injector Failure Symptoms
OM646 injectors fail in four field-recognisable patterns. The first is a no-start or extended-crank condition on a fully-warm engine — almost always a worn pintle or seized armature on a single cylinder. The second is heavy black smoke under acceleration combined with a measurable loss of pull above 2,500 rpm — symptomatic of over-fuelling on one or more cylinders. The third is rough idle with a perceptible knock that smooths out above 1,500 rpm, often misdiagnosed as turbo or top-end mechanical play. The fourth is excessive leak-back into the rail return system, surfacing as repeat hard-starts on a cold morning after the rail has bled down overnight.
Live-data diagnosis on Mercedes-spec scan tools (Star Diagnosis / XENTRY) is the fastest route to the failed unit. Read individual cylinder fuel-trim corrections, rail-pressure deviation at idle and during cranking, and run a cylinder-by-cylinder leak-off test before tear-down. A single injector returning more than the workshop manual permits at the rail-return port is the unit to replace.
Vehicles and Engine Codes Using the OM646 Injector
The 0445115069 / 0445115068 family is fitted across the W639 Sprinter (NCV3) 2.2 CDI 209/211/213/215/216/218 (OM646.984/985/986/990, 2006-2009), W639 Vito and Viano 2.2 CDI 109/111/115 (OM646.980/982, 2003-2010), W211 E-Class E200 / E220 CDI (OM646.821/961/984, 2002-2009), W203 C-Class C200 / C220 CDI (OM646.962/963, 2003-2008) and C209 CLK220 CDI (OM646.963, 2005-2009). The OM646.701 industrial sub-code is also covered by this Bosch CRIN family.
All variants share the same Bosch CRIN body, calibration class and copper sealing washer specification — meaning a 0445115069 unit will physically fit any of the above OM646 applications. What changes between vehicles is the ECU calibration map and the cylinder-position correction values, both of which live in the engine ECU rather than the injector itself.
Leak-Back, Hard Starting and Rough Idle
The single most accurate diagnostic for a failing OM646 injector is the leak-off (return-line) test. Disconnect the four return spigots, fit calibrated test bottles to each, crank the engine for 30-60 seconds and measure the volume returned per cylinder. Any injector returning materially more than its three siblings is the failed unit — even if the engine appears to be running smoothly under load.
Hard-start episodes that resolve after several seconds of cranking are almost always traceable to internal leak-back drying out the rail overnight. Rough idle that improves above 1,200 rpm is typically a single-cylinder over-fuelling event caused by a stuck-open injector — readable as a negative fuel-trim correction on that cylinder in live data.
Calibration and Injector Class Coding
Every Mercedes OM646 injector carries a factory calibration class (typically a single-letter or numeric code laser-marked on the body) which the ECU uses to compensate for unit-to-unit flow tolerance. After fitting a remanufactured 0445115069 / 0445115068 unit, the new calibration value MUST be programmed into the engine ECU against the correct cylinder index. On Sprinter, Vito, Viano, E-Class, C-Class and CLK applications this is done via Mercedes Star Diagnosis / XENTRY or a compatible aftermarket tool that supports CDI3 / CDI4 injector coding.
Skipping the calibration step is the most common cause of a freshly-fitted OM646 injector throwing immediate cylinder-balance, rail-pressure and EGR-flow fault codes. Every unit we ship is delivered with its individual calibration class clearly marked on the packaging and on the injector body itself.
Remanufacture and Bench-Calibration Specification
Each OM646 unit is fully stripped, ultrasonically cleaned, fitted with new Bosch genuine internal components (nozzle, pintle, armature, control valve), reassembled to OEM torque spec and bench-tested on Bosch CR918 / EPS 200 calibration equipment across idle, mid-range and full-load delivery profiles. Every unit ships with a printed test certificate showing actual flow values against the OEM tolerance window.
Each remanufactured injector includes the correct copper sealing washer, is supplied with a 12-month warranty, and qualifies for free UK delivery. A £20 refundable core surcharge applies — the surcharge is returned in full once your old core is received.
