John Deere Engines SPN105FMI4 Fault Code: Manifold Air Temperature Signal Out of Range Low
Also called Intake Manifold Air Temperature Signal Out of Range Low, Manifold Air Pressure Signal out of Range Low, Manifold Air Temperature Input Voltage Low
Manifold Air Temperature Signal Out of Range Low · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 105 FMI 4 means the ECU is reading a manifold air temperature (MAT) input voltage that has dropped below the sensor's low voltage specification, a level lower than physically possible intake air temperature. The engine falls back to a default MAT value of 60°C (140°F) or 50°C (122°F) depending on the application, and the ECU's high MAT engine protection feature is disabled. This is often shown as DTC 105.04 on some platforms.
Medium severity. The engine will keep running using a substituted MAT default value, but the ECU's high manifold air temperature protection is disabled while this code is active. That protection loss means the engine could run hotter intake charge conditions without the safeguard it normally has, so this should be diagnosed the same shift rather than ignored.
What does John Deere Engines error code SPN105FMI4 mean?
The manifold air temperature (MAT) sensor is a thermistor mounted in the intake manifold that measures the temperature of intake air. As a thermistor, its resistance changes with temperature, and that resistance change causes the input voltage the ECU sees to vary. Higher intake air temperatures produce lower MAT input voltages, while lower temperatures produce higher voltages. The ECU uses this input, together with the manifold air pressure (MAP) sensor, to calculate engine airflow.
SPN 105 FMI 4 sets when the MAT input voltage drops below the sensor's low voltage specification, a voltage so low it corresponds to a temperature that is not physically possible for manifold air. This points the ECU toward an electrical fault rather than an actual air temperature reading, most likely a short to ground or low resistance somewhere in the sensor circuit.
When this code sets, the ECU substitutes a default 'limp-home' MAT value, either 60°C (140°F) or 50°C (122°F) depending on the specific engine application, so the engine keeps running. At the same time, the ECU's high manifold air temperature engine protection feature is disabled, and a blinking warning light is set on applicable panels.
What triggers a John Deere Engines SPN105FMI4 code?
The manifold air temperature input voltage drops below the sensor's low voltage specification. For OEM applications this threshold is listed as 0.3 volts in one version and 0.1 volts in others, depending on engine application. On some platforms this is described as the input circuit seeing a voltage drop consistent with low resistance to ground (a grounded input circuit), since the circuit is designed to see voltage fall as resistance to ground decreases.
Common causes of SPN105FMI4
- Dirty, damaged, or poorly positioned terminals or connector at the ECU (including the ECU's 60-way or 30-way connector depending on application)
- Dirty, damaged, or poorly positioned terminals or connector at the manifold air temperature sensor itself
- An open or short in the wiring harness or circuits running to the manifold air temperature sensor, including a short to ground in the MAT input circuit
- A faulty manifold air temperature sensor
- A faulty ECU
How to troubleshoot John Deere Engines SPN105FMI4: first checks
- Without disconnecting connectors, visually inspect the ECU connector and the manifold air temperature sensor connector for contamination, damage, corrosion, or terminals that are pushed back or poorly seated.
- Inspect the wiring harness between the ECU and the MAT sensor for chafing, pinched sections, or damage that could cause a short to ground.
- When probing connectors for voltage checks, use a proper connector adapter test kit rather than forcing probes into the terminals, since forcing probes can damage the terminals and create a new fault.
- Check for corrosion or moisture intrusion at connector splices between the ECU and the sensor, since a short to ground in this circuit is a common way the input voltage collapses below spec.
- Test or swap the MAT sensor if wiring and connectors check out clean, since a failed sensor thermistor is a listed possible cause.
How the code clears
No separate clearing step is listed beyond repairing the underlying wiring, connector, sensor, or ECU fault. Once the MAT input voltage is restored to a normal operating range, the code should stop being active; if a stored code needs to be cleared with a diagnostic tool after the repair, follow the tool's standard procedure since no distinct reset procedure is given here.
Frequently asked questions
What does SPN 105 FMI 4 mean on a John Deere engine?
It means the manifold air temperature (MAT) sensor's input voltage to the ECU has dropped below the sensor's low voltage specification, to a level that corresponds to a temperature that isn't physically possible for intake air. The ECU treats this as a sensor circuit fault rather than a real high temperature reading.
Can I keep running the equipment with this code active?
The engine will typically keep running because the ECU substitutes a default MAT value (60°C/140°F or 50°C/122°F depending on application) to keep calculating airflow. However, the ECU's high manifold air temperature engine protection feature is disabled while the code is active, so it's best to get it diagnosed rather than run on it long-term.
What voltage triggers SPN 105 FMI 4?
On OEM applications the low voltage specification is listed as 0.3 volts in some documentation and 0.1 volts in others, depending on the specific engine application. Other applications may have their own specification listed separately in that engine's application specifications.
What is the most likely cause of this fault?
A short to ground or low resistance in the MAT sensor input circuit is called out as the probable cause on some platforms, since the circuit is designed to see voltage drop as resistance to ground decreases. Bad connectors or terminals at the ECU or sensor, an open or shorted harness, a bad MAT sensor, or a bad ECU are all listed possible causes.
Will a blinking warning light come on for this code?
Yes, on applicable platforms the ECU sets a blinking warning light when SPN 105 FMI 4 is active.
Is it safe to probe the connectors myself to check voltage?
Be careful. Forcing test probes directly into connector terminals can damage them and create a new fault. A proper connector adapter test kit is recommended for making measurements without damaging the terminals.
Does this code affect engine performance?
The ECU keeps the engine running using a default MAT value, so there may not be an obvious performance change, but the loss of the high manifold air temperature engine protection feature means a real high-temperature condition could go unprotected until the fault is fixed.