If your truck is showing SPN 84 FMI 3, it means the accelerator pedal position voltage is higher than expected. This can cause reduced throttle response, poor acceleration, or even engine derate depending on the severity.
What Does SPN 84 FMI 3 Mean?
- SPN 84 = Accelerator Pedal Position
- FMI 3 = Voltage Above Normal
This means the ECM is receiving a signal that is higher than expected from the accelerator pedal sensor.
Common Symptoms
- Reduced throttle response
- Engine derate
- Poor acceleration
- Check engine light
- Intermittent throttle operation
- Truck stuck at idle
Common Causes
- Bad accelerator pedal sensor
- Damaged wiring harness
- Loose connector
- Short to voltage
- Water intrusion
- ECM fault (rare)
How to Diagnose SPN 84 FMI 3
- Connect diesel diagnostic laptop
- Check live accelerator pedal data
- Inspect pedal wiring harness
- Check connectors for corrosion
- Test voltage using multimeter
- Replace faulty accelerator pedal sensor
Trucks Commonly Affected
- Freightliner
- International
- Kenworth
- Peterbilt
- Volvo
- Mack
Why You Need a Diesel Diagnostic Laptop
A diesel diagnostic laptop allows you to monitor live pedal data, confirm voltage readings, and quickly identify the cause without replacing unnecessary parts.
Need a Diesel Diagnostic Laptop?
Our dealer-level diesel diagnostic laptops help diagnose SPN 84 FMI 3 and thousands of other truck fault codes.