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∙ In MAN EDC diagnostics the fault text “NBF-Signal” (flash / blink / DTC code 1A) refers to the signal of the Nadel-Bewegungs-Fühler (NBF) – English: needle-lift / needle-movement sensor that is built into one fuel injector (the “pilot” or “master” injector, usually cylinder 4 on the 4-cyl. D08 engine).
∙ Loss, implausibility or complete absence of this feedback signal makes the ECU enter limp-home mode: the EDC warning lamp lights and engine speed is limited to ≈ 1 800 rpm.
∙ The fault is most often caused by an open/shorted sensor coil inside the injector or damaged wiring/connector, less frequently by an ECU input failure.
Key points
• NBF ≠ CAN bus fault – it is an injector feedback sensor fault.
• Measure injector-internal coil (≈ 80…120 Ω) and harness continuity first.
• Replace the complete injector if the coil is out of spec; repair wiring if damaged; only consider ECU after those two are ruled out.
Function of the NBF
• Bosch/MS5 EDC uses one “intelligent” injector containing a piezo-magnetic needle-lift sensor.
• ECU compares commanded SOI (start of injection) with the physical needle-lift signal to keep timing closed-loop and to learn pump delays.
• If the feedback is missing the ECU can no longer guarantee correct timing → switches to fixed, retarded map and torque/rpm limitation.
Failure modes that raise “NBF-Signal”
a. Electrical open circuit in sensor coil (most frequent).
b. Coil short to ground or between leads.
c. Harness damage / water ingress in connector.
d. Corrosion or pushed-back terminals.
e. Rare: ECU input stage defect.
Symptoms that match the user report
• EDC lamp permanently ON after start.
• Maximum engine speed ≈ 1 800 rpm, power reduced.
• Fault memory: “1A ‑ NBF Signal”, sometimes accompanied by “43 – engine speed limited”.
Why the CAN-bus interpretation is unlikely
• MAN service literature (MS5 / EDC 7 fault tables) explicitly labels 1A as “NBF-Signal (Injector 1 coil)” – see MAN bulletin 24.522/10.
• CAN faults are reported as “CAN KOM” or “BUS AUSFALL” with codes 31/32 etc.
• Therefore the “network bus fault” explanation conflicts with factory documentation.
• Modern MAN common-rail engines have replaced the NBF injector with crank-based timing strategies and rail pressure sensors; however older rotary-pump MS5 systems (1998-2006) still rely on NBF.
• Replacement injectors are available as OE MAN or Bosch exchange units; several remanufacturers now supply them with new coils.
• Trend: predictive maintenance—monitoring coil resistance drift during service to replace injectors before hard failures.
Electrical specs (typical Bosch MS5-equipped D0834/D0836 engines):
• Coil resistance (20 °C) …… 90 Ω ± 20 Ω
• Operating voltage ………… 5 V square wave from ECU, 10–40 mA signal amplitude
• Connector …………………… 2-pin, shielded twisted pair
Example scope trace:
• Rising edge when needle lifts ≈ 0.2 ms after pump delivery.
• Amplitude 4.5 V to 5 V; loss of pulse = NBF fault.
Analogy: Think of the NBF as the crank sensor for the injector—without confirming that the “valve” really opened, the ECU plays safe.
• Always depressurise fuel system and follow MAN service manual—common-rail pressures exceed 1 000 bar and can cause fluid-injection injuries.
• Use CE-approved test instruments; environmental regulations require proper disposal of diesel-contaminated parts.
Step-by-step troubleshooting (no oscilloscope needed at first):
Best practices
• Replace sealing washers when removing injectors.
• After injector replacement, bleed system and perform ECU adaptation if available in diagnostic tool.
• Store freeze-frame data before clearing codes for warranty documentation.
Potential challenges
• Seized injectors—use puller to avoid head damage.
• Misidentification of cylinders—follow firing order 1-3-4-2 on D0834.
• Resistance values may vary slightly by injector part number—always cross-check with MAN spare-parts catalogue using VIN.
• A single intermittent NBF dropout may not light EDC; persistent loss (> 1 s) triggers limp mode.
• Aftermarket “emulators” that bypass NBF are illegal in EU road vehicles and void type approval.
• Investigate predictive diagnostics—monitor NBF signal quality vs. operating hours.
• Examine piezo vs. inductive needle-lift technologies for future retrofit.
• Review MAN service bulletin “A-24-30/2023” on upgraded wiring looms with silicone insulation.
Recommended resources
• MAN EDC MS5 Instruction Manual (Chapter 5: error code list).
• Bosch Diesel System Training CD “Needle sensor injectors”.
• MAN-cats III diagnostic software user guide.
“NBF-Signal” on your MAN LE 8.140 does not indicate a CAN-bus problem; it flags a missing/implausible signal from the needle-lift sensor inside the dedicated NBF injector. The ECU therefore protects the engine by illuminating the EDC lamp and capping speed at ~1 800 rpm. Check injector coil resistance, wiring continuity and connector condition; in the vast majority of cases replacing the faulty injector rectifies the problem and clears the fault.
