SPN 1705 FMI 2: Meaning and Fix
SPN 1705 FMI 2 indicates the Forward View Imager System is sending erratic, intermittent, or incorrect data to the ECM via the J1939 CAN bus. This fault commonly appears after a camera replacement if the module is not properly calibrated or if there is a loose connector at the imager unit. Technicians also see this code after windshield replacements when the camera mounting bracket is misaligned, causing signal instability.
Common Symptoms
- Lane Departure False Alarms: Erratic imager data triggers frequent false lane departure warnings during normal straight-line driving.
- Adaptive Cruise Disabled: The system deactivates adaptive cruise control due to unreliable forward object distance measurements.
- Collision Warning Malfunction: Intermittent or missing forward collision alerts, reducing driver confidence in the safety system.
- Instrument Cluster Warning: Amber warning light for the forward imager system illuminates on the dash with a logged J1939 fault.
Probable Causes
- Loose Imager Connector: Vibration causes intermittent contact at the 6-pin camera connector, corrupting video data frames.
- CAN Bus Termination Error: Improper termination resistance on the imager’s CAN branch leads to signal reflection and data corruption.
- Moisture Ingress: Water intrusion into the camera housing disrupts internal electronics, causing intermittent output signals.
- ECM Software Mismatch: Outdated ECM calibration incompatible with the imager firmware, leading to data interpretation errors.
Advanced Technical Analysis
The ECM monitors the Forward View Imager’s CAN message rate and checksum integrity. When the imager sends frames with invalid cyclic redundancy check (CRC) or inconsistent sequence counters, the ECM sets FMI 2. This indicates data is present but corrupted. The ECM debounces the fault over 3 consecutive seconds before activating the diagnostic trouble code.
Electrical analysis focuses on the imager’s power supply (12V/24V) and ground stability. A voltage drop below 10.5V during engine cranking can cause the imager’s internal processor to reset, producing erratic data. Oscilloscope testing at the imager’s CAN_H and CAN_L lines should show a clean differential signal between 1.5V and 3.5V without glitches.
Upon detecting erratic imager data, the ECM enters a safety fallback mode. It disables adaptive cruise control and forward collision warning, but retains basic engine operation. No torque derate is applied because the fault is perception-based, not engine-critical. The system will automatically recover if the imager sends valid data for 10 consecutive seconds.
Long-term prevention requires verifying the imager’s mounting torque (typically 2.5 Nm) and using dielectric grease on the connector. Real-world example: A fleet of delivery trucks repeatedly experienced SPN 1705 FMI 2 after automatic car washes. Investigation revealed that high-pressure water forced past the camera seal, causing intermittent shorts. Replacing the seal and applying conformal coating to the PCB resolved the issue permanently.
Step-by-Step Troubleshooting Guide
- Inspect Connector: Remove and reseat the imager connector. Check for bent pins, corrosion, or moisture. Apply dielectric grease.
- Verify CAN Bus: Measure termination resistance between CAN_H and CAN_L at the imager connector. Must be 60 ohms.
- Check Power Supply: Measure voltage at the imager’s power pin during key-on and engine crank. Must stay above 10.5V.
- Update Calibration: Flash the ECM with the latest factory calibration to ensure compatibility with the imager firmware version.