Truck Fault Codes

FMI 5 Explained

FMI 5 generally means the current is lower than expected, often suggesting an open circuit or weak connection. The final interpretation depends on the SPN, source address, OEM calibration, active status, and related codes.

Review status: source-backed medium Last reviewed: 2026-04-14

What This FMI Means

FMI 5 indicates the current flowing in the monitored circuit is low of the expected range. Unlike voltage FMIs (3 and 4) which monitor sensor input circuits, current FMIs appear on output circuits where the module drives a load — solenoids, injectors, relay coils, and actuators.

The module measures how much current its output driver is supplying to the connected load. A low current reading means the load is not drawing the expected current — which points to open circuits, broken wires, a failed actuator coil, or a disconnected load.

How It Appears With SPN Codes

FMI 5 most commonly appears on solenoid-driven SPNs: fuel injectors (SPN 651–658 for cylinders 1–6), EGR valve actuators, VGT turbocharger actuators, transmission shift solenoids, and retarder control solenoids. These are high-current output circuits where the module actively monitors current draw.

On Cummins ISX and ISB engines, FMI 5 on an injector SPN (651–658) is a classic open injector circuit. On Allison Transmission controllers, FMI 6 on shift solenoid SPNs indicates a shorted solenoid coil. OEM service information specifies the resistance range and expected current draw for each circuit.

How to Approach Diagnosis

Measure the component's resistance with a digital multimeter before removing anything. The actuator or solenoid coil has a specified resistance range in the OEM service manual. an open circuit (infinite resistance) confirms the component is failed or the harness is broken.

If the coil measures within specification, inspect the harness for broken wires, corroded terminals, or a pin that has backed out of the connector body. Resistance measurements at both the component end and the module connector identify where in the circuit the fault exists.

What Drivers Should Record

Record the full SPN/FMI along with all related codes active at the same time. Current faults on injector circuits may accompany rough-running or cylinder-misfire symptoms; current faults on solenoid circuits may accompany shift quality complaints, actuator hesitation, or warning lamps for the affected system.

Note whether the fault appeared after recent maintenance — reconnected injector harnesses with damaged pins, swapped solenoids with incorrect resistance specifications, or connector repairs are common triggers for FMI 5 and FMI 6 codes. This context tells the technician where to look first.

Related Pages

Related Fault Code Pages

Sources

  • SAE J1939 Standards Collection SAE International · official · accessed 2026-05-05 · confidence medium

    Source: SAE International, SAE J1939 Standards Collection. This page paraphrases factual fields only and is not a substitute for the original document.

    Open source
  • NHTSA Manufacturer Communications Search National Highway Traffic Safety Administration · government · accessed 2026-05-05 · confidence high

    Source: National Highway Traffic Safety Administration, NHTSA Manufacturer Communications Search. This page paraphrases factual fields only and is not a substitute for the original document.

    Open source

FAQ

What does FMI 5 (current low) tell me about what might be wrong?

FMI 5 indicates the current measured in that circuit is low of the expected range. This FMI typically appears on output circuits — solenoids, injectors, actuators — where the module is measuring how much current the connected load draws. A current low reading most often points to an open circuit, a broken wire, a failed actuator coil, or a loose connector.

Can FMI 5 appear on a sensor, or only on actuators and solenoids?

Current monitoring (FMI 5 and 6) is most commonly seen on output circuits where the module drives a load — injectors, solenoids, relays, actuators. Sensors are more typically monitored by voltage (FMI 3, 4). If FMI 5 appears on a sensor SPN, the specific circuit design for that sensor includes current monitoring, which is less common but possible on some module designs.

If FMI 5 appears after replacing a solenoid or actuator, what should be checked?

After replacing a component on an FMI 5 circuit, confirm the connector is fully seated and the pins are not bent or corroded. Also verify that the replacement part has the correct resistance specification — an actuator with the wrong coil resistance will produce a current low reading even if it is otherwise functional. Measuring the coil resistance with a multimeter before reinstalling confirms the part is correct.