Cummins Generator SPN 94 FMI 4 Error Code Explained: Meaning, Causes & Fixes

What Does SPN 94 FMI 4 Mean on a Cummins Generator?

If your Cummins generator is displaying the SPN 94 FMI 4 error code, it means there's a problem with low battery voltage detected by the engine control module. SPN stands for Suspect Parameter Number (which is the location of the issue), 94 is the code for the battery voltage, and FMI 4 refers to a voltage below the normal operating range. This is a warning—it generally means your generator’s battery isn't getting or holding a proper charge, or there is an electrical connection issue.

Immediate Actions to Take for SPN 94 FMI 4 Error

When you see this error, start by turning off your generator if it’s safe to do so. Safety always comes first. You want to prevent additional electrical stress or damage to the generator's sensitive components.

Steps to Fix the SPN 94 FMI 4 Error

• Check the Battery Voltage Directly
  Use a basic multimeter (a tool that measures electrical voltage) to check the voltage across the battery terminals. For most Cummins generators, a healthy battery should show about 12.6 to 12.8 volts when the engine is off. If it’s much lower (especially below 12 volts), the battery is likely discharged or faulty.
• Inspect Battery Terminals and Connections
  Look at the battery terminals—these are where the generator’s wires connect to the battery. Check that the terminals are tightly connected and clean, without corrosion (white or greenish build-up). If you see corrosion, disconnect the battery (always remove the negative/black cable first), then clean the terminals and cable ends using a wire brush or battery terminal cleaner.
• Examine Battery Cables and Wires
  Inspect all cables running from battery to the generator. Make sure there are no loose, frayed, or damaged wires. Pay special attention to the cable crimp connections and that all bolts are snug. A single loose connection can cause this fault.
• Test Battery Health
  If the battery voltage is low, try to charge it with a battery charger. After charging, disconnect the charger and let the battery sit for about half an hour, then measure again. If it drops quickly back below 12 volts, the battery may need to be replaced. Replacement is usually straightforward, but be sure to get the correct Cold Cranking Amps (CCA) and voltage for your Cummins generator.
• Inspect the Alternator and Charging System
  When the generator is running, the alternator is responsible for recharging the battery. Use your multimeter to measure voltage at the battery with the generator running—expect 13.5-14.5 volts. If you’re not seeing a voltage increase, there may be a charging system problem, such as a bad alternator, faulty voltage regulator, or wiring issue.
• Check for Parasitic Drains
  Sometimes, things like faulty relays or control boards may be draining the battery even when the generator is off. With the generator off, disconnect the negative battery cable, and use a multimeter in “amps” mode between the cable and the battery post. If you see a steady drain, you’ll need to trace and isolate the culprit, possibly with the help of a technician.
• Review Recent Service or Changes
  If you’ve recently had work done on your generator, double-check that all battery and alternator connections were properly reattached. Something may have been left loose.

When to Call a Professional Technician

If these checks don't resolve the warning, or you aren’t comfortable with electrical work, it's time to contact a professional who understands Cummins generators. In both St Louis and Nashville, it's important to choose a service team that understands your specific generator brand and can safely handle electrical diagnostics. An expert technician will have advanced equipment to check the generator control modules for stored fault codes and use factory-approved tests.

They can also spot less common issues, like hidden wiring faults, charging circuit failures, or software glitches in the control system that could also result in SPN 94 FMI 4. Reliable companies in St Louis and Nashville should be familiar with both commercial and residential generator systems.

Tips to Prevent SPN 94 FMI 4 in the Future

• Keep battery terminals clean and free from corrosion.
• Test your generator battery at least once a year to ensure it holds a charge.
• Ensure generator exercise cycles (automatic weekly run) are enabled; they help keep the battery charged.
• Check the generator's charging system as part of regular service.
• Replace worn-out batteries promptly—don’t wait for them to completely fail.

By following this process, most SPN 94 FMI 4 errors can be tracked down to either a simple battery issue or an obvious wiring connection. If your generator powers critical loads at your home or business in St Louis or Nashville, fast resolution is important. Never ignore this error, as low battery voltage can lead to more serious generator problems down the line.