John Deere Engines SPN108FMI2 Fault Code: Barometric Pressure Signal Invalid
Also called Barometric Air Pressure Signal Invalid
Barometric Pressure Signal Invalid · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 108 FMI 2 means the ECU's internal barometric air pressure sensor is sending a reading that doesn't match the estimated barometric pressure the ECU calculates. This is a Warning-level code, the engine keeps running using a backup value, but it should still be looked at soon.
Low severity. This code is listed at Warning alarm level. The ECU automatically substitutes a working value so the engine keeps running, but an invalid internal sensor reading should be diagnosed to rule out a failing ECU.
What does John Deere Engines error code SPN108FMI2 mean?
SPN 108 FMI 2 is set when the ECU compares the reading from its internal barometric air pressure sensor against an estimated barometric pressure value and finds the two don't agree, meaning the signal is considered invalid.
The barometric air pressure sensor referenced here is built into the ECU itself, not a separate external sensor. It cannot be repaired or replaced on its own; if it's bad, the ECU itself is the problem.
When this code sets, the ECU doesn't shut the engine down. Instead it substitutes intake manifold air pressure as the barometric pressure value. If that manifold reading is also invalid, the ECU falls back further to a default fixed value of 101 kPa (1 bar, 14.6 psi) so the engine can keep running.
Common causes of SPN108FMI2
- Debris or dirt blocking the small air vent located on the side of the ECU housing
- Outdated ECU software
- A bad ECU (the internal barometric sensor itself has failed and cannot be repaired separately)
How to troubleshoot John Deere Engines SPN108FMI2: first checks
- Inspect the air vent on the side of the ECU housing for dirt, debris, or blockage and clean it if restricted.
- Check with your dealer or service tool whether the ECU software is current and update it if an outdated version is found.
- If the vent is clear and software is current, plan on ECU diagnosis or replacement, since the internal sensor cannot be serviced separately.
- Confirm the engine is running normally on the backup pressure value (manifold air pressure or the 101 kPa / 14.6 psi default) while you troubleshoot, since performance may be slightly affected by the substituted value.
How the code clears
No separate clearing step is listed. Address the underlying cause (clean the ECU air vent, update ECU software, or replace the ECU if it's bad) and the code should clear once the ECU receives a valid barometric pressure reading again.
Frequently asked questions
What does SPN 108 FMI 2 mean on a John Deere engine?
It means the ECU's internal barometric air pressure sensor reading doesn't match the ECU's own estimated barometric pressure, so the signal is flagged as invalid.
Can I keep running the machine with this code active?
The code is a Warning level alarm, not a shutdown. The ECU automatically substitutes intake manifold air pressure, or a default of 101 kPa (14.6 psi) if that's also invalid, so the engine keeps running while you diagnose the cause.
Can the barometric air pressure sensor be replaced by itself?
No. The barometric air pressure sensor is built into the ECU and cannot be repaired or replaced separately. A confirmed bad sensor means the ECU itself needs attention.
What's the most common fix for this code?
Start by checking the small air vent on the side of the ECU for dirt or blockage and clean it. Outdated ECU software is another listed cause, so a software update is worth checking before assuming the ECU itself is bad.
Will this code affect engine performance?
It shouldn't cause a major performance change since the ECU substitutes a working pressure value, but relying on a default or estimated value instead of a real sensor reading isn't ideal for long-term operation, so it should be diagnosed rather than ignored.
Is there a specific reset procedure for this code?
No reset procedure is listed for this code. Clearing it depends on fixing the underlying cause, such as clearing a blocked ECU air vent, updating software, or addressing a bad ECU.