If your diesel truck is showing SPN 111 FMI 3, you’re dealing with a battery voltage too high fault — one of the most common electrical issues across Cummins, Detroit, Paccar, Volvo, and Freightliner trucks.

This guide will show you exactly what it means, what causes it, and how to diagnose and repair it using a truck scanner.

🔍 What SPN 111 FMI 3 Means

• SPN 111 → System Voltage

• FMI 3 → Voltage above normal or overvoltage

This means your truck’s ECM is seeing voltage too high, usually above 16V. If ignored, it can damage the ECM, sensors, and aftertreatment components.

⚠️ Common Symptoms

Drivers often report:

• Dash lights flickering

• Blowing fuses

• Intermittent shutdowns

• Battery light ON

• Alternator running hot

• Random “ghost” codes

• Poor or failed regens

Electrical faults can trigger aftertreatment codes, so this one must be fixed ASAP.

🔧 Common Causes of SPN 111 FMI 3

Here are the most likely causes, in order:

✔️ Failing alternator (overcharging)
✔️ Bad voltage regulator
✔️ Loose or corroded grounds
✔️ Damaged battery wiring
✔️ Incorrect alternator installed
✔️ Faulty battery isolator (common on fleet trucks)
✔️ Jump-start voltage spikes

This code almost always points to an alternator/regulator issue.

🛠️ How to Diagnose SPN 111 FMI 3 Using a Truck Scanner

You’ll need a truck scanner such as:

• DieselScanners Laptop Kit

• Insite, DDDL, Texa, JPRO

• RP1210 adapter (USB-Link 2)

Step 1 — Scan and Confirm the Code

Look for these additional clues:

• SPN 168 FMI 3/4 (battery voltage abnormal)

• SPN 523 FMI 3 (ECM voltage high)

• SPN 636 FMI 3 (sensor reference voltage high)

These confirm electrical overvoltage.

Step 2 — Check Live Voltage in the ECM

Using your truck scanner, check:

• Charging voltage

• Battery voltage

• Alternator output

Normal running voltage should be 13.5–14.7V.

If you see 15.5V+, it’s overcharging.

Step 3 — Inspect Alternator and Regulator

Look for:

• Loose alternator cables

• Bad or corroded grounds

• Alternator overheating

• Wrong part number on replaced alternator

Many “new” alternators come with faulty regulators.

Step 4 — Load Test the Batteries

Weak or sulfated batteries can cause voltage spikes.

Replace if needed.

Step 5 — Clear the Code and Recheck

After repairs:

• Clear SPN 111 FMI 3

• Check charging voltage while idling and revving

• Look for any new electrical codes

If the voltage stays stable, the issue is fixed.

⭐ Pro Tip:

If your truck recently had a dead battery and someone jump-started it with a high-amp setting, that alone can trigger SPN 111 FMI 3.

Always ask the driver what happened before the fault appeared.

📘 Tools You’ll Need

• Truck scanner laptop

• RP1210 adapter (Nexiq USB-Link 2 recommended)

• Digital multimeter

• Replacement alternator or voltage regulator (if needed)

✅ Final Summary

SPN 111 FMI 3 means overvoltage, usually caused by a bad alternator or regulator. Using a truck scanner, you can:

✔️ Confirm voltage values
✔️ Diagnose related electrical faults
✔️ Verify repairs
✔️ Safely clear the code

Fixing this early prevents ECM damage, failed regens, and expensive electrical failures.