SPN 3661 FMI 13: Meaning and Fix
SPN 3661 FMI 13 indicates the Engine Fuel 1 Injector Cylinder 3 Actuator 2 (second valve actuator) has fallen out of calibration range. This fault commonly appears after a forced DPF regeneration or ECM replacement, where the actuator’s learned zero-position is lost. The ECM detects a deviation between commanded and actual actuator position, triggering a derate. Technicians frequently encounter this after swapping injector harnesses without recalibrating.
Common Symptoms
- Rough Idle: Cylinder 3 misfire at idle due to incorrect injection timing from uncalibrated actuator 2.
- Power Loss: Engine torque derate up to 30% as ECM limits fuel to protect actuator integrity.
- MIL Illuminated: Red stop lamp and amber warning lamp activate; J1939 broadcast active fault.
- Hard Starting: Extended cranking time because ECM fails to synchronize cylinder 3 fuel delivery.
Probable Causes
- ECM Calibration Loss: Recent ECM flash or battery disconnect erases learned actuator zero-point for cylinder 3.
- Actuator Wear: Mechanical wear on actuator 2 plunger alters stroke length beyond calibration window.
- Harness Resistance: Increased resistance in injector harness (pin A/B) shifts actuator feedback voltage.
- Oil Contamination: Fuel dilution in engine oil degrades actuator solenoid performance, skewing calibration.
Advanced Technical Analysis
The ECM monitors actuator 2 position via a Hall-effect sensor returning a 0.5–4.5 V signal. During key-on, the actuator performs a self-learn stroke to define min and max positions. If the learned travel deviates more than ±5% from factory limits stored in EEPROM, FMI 13 sets. On MAN D26 engines, this threshold is ±3% per factory spec.
Electrical analysis shows the actuator coil resistance should measure 1.2–1.8 Ω at 20°C. The ECM applies a 12 V PWM signal at 200 Hz and reads back position. A debouncing timer of 1.2 seconds prevents false triggers. If the actuator fails to reach commanded position within 10 cycles, the fault latches permanently until a successful calibration cycle completes.
Upon detecting the out-of-calibration condition, the ECM deactivates actuator 2 and switches cylinder 3 to a fixed injection timing map. This causes a 20–30% torque derate and forces the engine into limp-home mode. On Deutz TCD 7.8 engines, the ECM also inhibits diesel exhaust fluid dosing to prevent aftertreatment damage from unburned fuel.
Long-term prevention requires performing an injector calibration routine using a factory diagnostic tool (e.g., Bosch ESI[tronic] or MAN CATS). A real-world example: after replacing the ECM on a Mercedes-Benz OM471, technicians must run the ‘Actuator Learn’ procedure three times consecutively. Skipping this step results in recurring SPN 3661 FMI 13 within 50 engine hours.
Step-by-Step Troubleshooting Guide
- Verify Fault Status: Connect diagnostic tool; confirm SPN 3661 FMI 13 is active and not historical. Record freeze frame data.
- Inspect Harness: Measure resistance between ECM pin 45 and actuator 2; must be below 0.5 Ω. Check for chafing.
- Perform Calibration: Use manufacturer software to execute ‘Injector Cylinder 3 Actuator 2 Learn’ routine. Cycle ignition.
- Test Actuator: Apply 12 V DC to actuator pins; listen for audible click. Replace if no response or intermittent.