What is SPN 788 FMI 7:
SPN 788 FMI 7 is a diagnostic trouble code (DTC) indicating a fault with the Air Compressor Discharge Pressure Sensor - Out of Range, High. This means the engine control module (ECM) has detected that the air compressor discharge pressure sensor is reporting a pressure value higher than the expected limit, which can affect the air brake system and overall vehicle safety.
Why This Happens
Common causes of SPN 788 FMI 7 include:
- Faulty or damaged air compressor discharge pressure sensor.
- Blockages or restrictions in the air compressor or related lines.
- Wiring issues such as open circuits, shorts, or damaged connectors.
- Faulty ECM or sensor calibration problems.
- Air leaks or malfunctions in the compressor system.
How to Fix It
To resolve SPN 788 FMI 7:
- Inspect the air compressor discharge pressure sensor for damage or contamination.
- Check air lines and fittings for blockages, leaks, or restrictions.
- Examine wiring and connectors for corrosion, breaks, or loose connections.
- Test the sensor for proper voltage and resistance values.
- Replace the sensor if faulty.
- Repair or replace any damaged wiring or connectors.
- Clear the fault code and verify air pressure readings and system operation.
How to Avoid It Before It Happens
To prevent SPN 788 FMI 7:
- Perform regular maintenance on the air compressor system.
- Keep air lines and fittings clean and free of obstructions.
- Inspect sensor wiring and connectors routinely.
- Use OEM-quality replacement parts and maintain proper system calibration.
- Use Clue’s Preventive Maintenance to schedule regular checks of the air compressor system, ensuring all components are functioning within their specified ranges and minimizing potential faults.
