What is SPN 523548 FMI 2 & How to Solve It?

What is SPN 523548 FMI 2:

SPN 523548 is a proprietary or OEM-specific code, and FMI 2 means data is erratic, intermittent, or incorrect.

This code is commonly seen on modern CAT and Cummins equipment and often relates to module communication, speed signals, or load control inputs.

‍

Why This Happens

• Faulty speed sensor or input sensor.
• Wiring short or intermittent connection.
• Module receiving unstable signal data.
• Software bug or signal filtering issue.
• Internal sensor degradation under load.

‍

How to Fix It

1. Use OEM software to identify the module or system triggering the code.
2. Check the relevant sensor and wiring for damage or disconnection.
3. Perform continuity and signal stability testing.
4. Replace sensor if readings are erratic even when engine is stable.
5. Clear the code and verify stable signal input during operation.

‍

How to Avoid It Before It Happens

1. Replace signal sensors during scheduled overhauls.
2. Test sensor readings under load, not just at idle.
3. Maintain clean and sealed connectors across data lines.
4. Log fluctuating sensor data before faults appear.

‍