SPN 3661 FMI 9: Meaning and Fix
This fault indicates the ECM has not received a valid CAN message from the injector actuator 2 on cylinder 3 within the expected update rate. In practice, this code often appears after replacing the ECM or injector harness without performing a correct parameter reset, causing the actuator to drop off the bus.
Common Symptoms
- Misfire Cylinder 3: Cylinder 3 fuel delivery is intermittent or absent, causing a noticeable misfire at idle and under load.
- Reduced Engine Power: ECM activates torque derate to protect the aftertreatment system, limiting engine output to around 50%.
- Rough Idle: Engine idles unevenly with increased vibration, especially at low RPM, due to inconsistent injection.
- Check Engine Lamp On: Amber warning lamp illuminates immediately, and the fault is logged as active or inactive in the ECM memory.
Probable Causes
- CAN Bus Wiring Fault: Open or short circuit in the CAN H or CAN L wires between the ECM and the injector actuator.
- Injector Actuator Failure: Internal electronic failure of the actuator 2 on cylinder 3, often due to thermal stress or vibration.
- ECM Software Mismatch: Incorrect or outdated ECM calibration file that does not match the injector actuator firmware version.
- Connector Corrosion: Moisture ingress at the actuator or ECM connector causing intermittent contact and message loss.
Advanced Technical Analysis
The ECM monitors the periodic CAN message from injector actuator 2 on cylinder 3. If the message is not received within a predefined time window (typically 50-100 ms), the ECM sets SPN 3661 FMI 9. This is a bus-level fault, not a physical injection failure. Real-world examples include actuator replacement without reflashing the ECM, causing a baud rate mismatch.
Electrical analysis focuses on the CAN bus termination and signal integrity. A missing or incorrect termination resistor (120 ohms) at the actuator can cause reflections, leading to corrupted messages. Technicians should measure resistance between CAN H and CAN L at the actuator connector; values outside 50-70 ohms indicate a wiring issue. This fault often follows a DPF regeneration event where thermal cycling stresses the harness.
When the fault is active, the ECM enters a safety fallback strategy: it cuts fuel to cylinder 3 completely and derates torque by up to 30%. The aftertreatment system may also be disabled to prevent damage from unburned fuel. In some MAN engines, the ECM forces a stationary regeneration after clearing the fault to ensure the DPF is not loaded with soot from the misfire.
Long-term prevention requires verifying that all injector actuators have matching firmware versions during ECM reprogramming. In Deutz TCD 2015 engines, this fault is common after a forced DPF regeneration when the actuator overheats. Technicians should always inspect the actuator O-ring and connector seal for heat damage. Replacing the actuator and performing a ‘Injector Actuator Learn’ procedure is mandatory.
Step-by-Step Troubleshooting Guide
- Scan for Active Codes: Use a J1939 diagnostic tool to read all active and inactive faults. Note any related bus or power supply codes.
- Inspect CAN Harness: Check continuity of CAN H and CAN L wires between ECM and cylinder 3 actuator. Look for chafing or corrosion.
- Measure Actuator Resistance: Disconnect actuator and measure resistance between pin 1 and 2. Expected value is 3-5 ohms; open indicates failure.
- Perform Actuator Relearn: After repair, use the diagnostic tool to run the injector actuator learn procedure to synchronize the ECM and actuator.