What does Caterpillar fault code SPN 108 FMI 4 mean?

Q: What does Caterpillar fault code SPN 108 FMI 4 mean?

SPN 108 FMI 4 indicates: Engine is "lazy"; Poor fuel economy; Struggles at high altitude. Fix: Barometric Pressure Voltage Low. LOGIC: Signal < 0.5V (Short to Ground). The ECM thinks the machine is at 15,000+ ft and cuts fuel to prevent smoke. ACTION: 1. Unplug sensor; check if code changes to FMI 3. 2. Check for 5V supply and ground. 3. Ensure the sensor atmospheric vent isn't plugged with mud. FIX: Replace Baro Sensor or repair signal wire shorted to frame.

Caterpillar Fault Code

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SPN 108 FMI 4

Engine is "lazy"; Poor fuel economy; Struggles at high altitude.

System

Not specified

Symptom

Engine is "lazy"; Poor fuel economy; Struggles at high altitude.

Diagnosis & fix steps

Barometric Pressure Voltage Low. LOGIC: Signal < 0.5V (Short to Ground). The ECM thinks the machine is at 15,000+ ft and cuts fuel to prevent smoke. ACTION: 1. Unplug sensor; check if code changes to FMI 3. 2. Check for 5V supply and ground. 3. Ensure the sensor atmospheric vent isn't plugged with mud. FIX: Replace Baro Sensor or repair signal wire shorted to frame.

Red Seal field insights

These sensors have a small "breather" hole. If you pressure wash the engine and force water into that hole, it will short the sensor internally.

Same code keeps coming back?

That's a program problem, not a part problem. Book a 30-minute uptime review with Grant, a Red Seal Heavy Duty Technician.

Book an uptime review

Read before you touch anything

This is general reference information, not a repair manual. It is for trained, qualified technicians.
Fault codes, meanings and procedures vary by model, serial number and software version. Confirm the code and the procedure against the manufacturer's service manual before acting.
Follow the OEM service manual, torque specs and your site's safety procedures: lockout/tagout, block raised equipment, relieve hydraulic, fuel and air pressure, and let hot systems cool.
You use this information at your own risk. Adventure Mechanical and AM Fleet Integrity accept no liability for damage, injury, downtime or loss arising from its use.
Not affiliated with or endorsed by any manufacturer. Brand names are used only to identify the equipment a code applies to.

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