Here’s a detailed description of the fuel injector used in the D40 Navara with the YD25 engine, including key specs, part numbers, function, and installation/compatibility notes.

1. What it is & how it works

The YD25 2.5 L diesel (in the Navara D40) uses common rail direct injection technology. 

• The injector is a high-pressure unit that injects diesel fuel directly into the combustion chamber (or pre-chamber depending on version) at the correct time and in the correct quantity.
• It’s electronically controlled: a solenoid or piezo actuator operates a nozzle that sprays fuel in a fine spray pattern for optimal combustion.
• Because it’s common rail, the fuel rail supplies very high pressure independently of engine speed, and the injectors fire when commanded by the engine control module (ECU).
• The injector must match calibration/sample-code for each cylinder so the ECU knows the precise characteristics of each injector. This is critical for clean combustion, emissions, performance and reliability.  

2. Key part numbers & fitment

Important injector part numbers for the YD25 in the D40 frame include:

• OEM part number: 16600-5X00A (and variants) for earlier/common versions.  
• Another part listed: Denso part number 295050-0300 for Spain-built D40 (from about April 2010 onward) for YD25.  
• Remanufactured injector numbers: 095000-6250 (for instance) listed for YD25.  

Fitment notes:

• Vehicle: Nissan Navara D40 (2.5 L YD25 diesel) and also the Pathfinder R51 with the same engine family.  
• Built dates matter: Spain-built vs Thai-built differ. For example one listing says Spain built D40 (from 04/2010) uses part 295050-0300.  
• Always check your VIN and original injector stamping/part number before ordering replacement.

3. What happens when the injector fails or is out-of-spec

An injector on this engine could show problems like:

• Rough idle, mis-fire in a cylinder.
• Excessive smoke (black or white) during acceleration or load.
• Loss of power, poor fuel economy.
• Check engine light / fault codes (e.g., injector circuit fault, mis-fire, emissions fault).
• Hard to start, especially when cold or under load.
  Because the injector timing/quantity is critical and they are matched to ECU calibration, a mismatched or faulty injector can lead to uneven cylinder pressures, bad combustion, and high emissions.

4. Replacement / coding / installation considerations

When replacing injectors in the D40 YD25 engine, you should consider:

• The new or remanufactured injector must match the specification and part number for your build year/region.
• After fitment, coding or calibration may be required: one source states ''The supplied common rail injectors **require coding to each cylinder by an authorised workshop that hosts the correct diagnostic equipment.''''  
• Use correct seals, washers, and follow torque specs for injector hold-down bolts or clamp.
• Ensure the fuel rail, high-pressure pump, and related system are in good condition (dirty rail, degraded pump, or poor fuel quality accelerate injector wear).
• If you fit a used or reman unit, ensure it has been properly tested and has correct injection quantity/setting matched to your engine. Some aftermarket listings emphasize ''remanufactured to OEM standards''.  
• On the YD25, because it’s common rail and many versions exist (Euro IV, Euro V etc.), ensure the correct injector for your emissions/rate engine (for example the high-power vs mid-power variants).  

5. Compatibility & fitment pitfalls

• Some users ask if D40 YD25 injectors will fit a D22 YD25. There are differences in engine build/rail/ECU, so compatibility is not guaranteed.  
• Always verify your VIN, engine stamp, build date and original part numbers.
• If the injector is coded and the ECU expects a particular code, installing a non-coded or wrong coded injector may lead to ECU errors or poor performance.
• Ensure return lines, O-rings, washers are in good shape. Diesel injection systems run at very high pressures, and any leak or poor seal will affect performance.

6. Summary of injector specs (typical)

Here is a summary of typical characteristics for the injectors used in YD25/D40: