John Deere Engines SPN105FMI15 Fault Code: Manifold Air Temperature Signal Slightly High
Also called Intake Manifold Air Temperature Signal Slightly High
Manifold Air Temperature Signal Slightly High · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN105FMI15 means the ECU sees the manifold air temperature (MAT) signal running slightly higher than expected for the current operating conditions, while the engine is running. It sets as a Warning level code, and the ECU tries to maintain proper operating conditions rather than derating the engine. The engine must run for a minimum of 3 minutes before this code can go active.
Medium severity. This is a Warning level code, not a derate. The ECU responds by trying to hold proper operating conditions rather than cutting power. Still, a high intake air temperature signal points to real airflow, cooling, or sensor problems that can get worse or lead to bigger issues like turbo or EGR damage if ignored.
What does John Deere Engines error code SPN105FMI15 mean?
SPN 105 is the manifold air temperature (MAT) sensor, which tells the ECU how hot the air entering the intake manifold is after it passes through the turbocharger and charge air cooler. The ECU uses this reading to manage fueling, boost, and emissions systems like EGR.
FMI 15 means the signal is valid but reads slightly higher than the ECU expects for the current conditions. This is different from FMI 0, which on this same SPN indicates the ECU sensed a manifold air temperature of 120° C (248° F). FMI 15 is a lesser, earlier warning: the reading is elevated but not yet at that hard threshold.
Because this code is a Warning, the ECU keeps running and simply tries to maintain proper operating conditions. It does not by itself force a derate on this specific fault mode, but repeated overheated intake air can strain the turbocharger, charge air cooler, and EGR system over time.
What triggers a John Deere Engines SPN105FMI15 code?
The manifold air temperature signal reads slightly higher than expected for the operating conditions that set the code. The engine must be running for a minimum of 3 minutes before the DTC can become active.
Common causes of SPN105FMI15
- Plugged air filter restricting intake airflow
- Charge air cooler plugged externally or internally, reducing its ability to cool compressed air
- Loose fan belt reducing cooling fan speed
- Exhaust leak
- Boost leaks in the charge air system
- Damaged fan shroud reducing airflow across the cooler
- EGR flow sensor venturi bracket loose or broken
- Bad connector or terminals at the MAT sensor
- Open or short in the wiring harness
- Bad MAT sensor
- Bad ECU software
- Internal charge air cooler plugging
- VGT (variable geometry turbocharger) vanes sticking
- Plugged EGR circuit or EGR system leak
- EGR flow sensor reading low
- Air throttle restriction
- Exhaust restriction
- Damaged turbocharger
- VGT vane position sensor giving an inaccurate reading
How to troubleshoot John Deere Engines SPN105FMI15: first checks
- Inspect and if needed replace the air filter for plugging or restriction
- Check the charge air cooler (front and rear of the core) for external debris, mud, or damage blocking airflow
- Check the fan belt for looseness and the fan shroud for cracks or damage that would reduce cooling airflow
- Inspect intake and exhaust piping for leaks, loose clamps, or boost leaks that would let hot air bypass proper cooling
- Check the MAT sensor connector and terminals for corrosion, looseness, or damage
- Inspect the wiring harness between the MAT sensor and ECU for opens or shorts
- If the engine has an EGR temperature sensor and related EGR temperature codes are also set, test the EGR valve for correct opening and closing and replace it if it does not operate correctly
- Check the EGR flow sensor venturi bracket for looseness or damage
- Look for exhaust restrictions and inspect the turbocharger and VGT vanes for sticking or damage
How the code clears
No separate clearing step is listed for this code beyond running the diagnostic procedure and confirming the fault condition is no longer present. Once the root cause is repaired, the code should stop being active on its own as the manifold air temperature signal returns to a normal, expected range for the operating conditions. No reset procedure is listed for this code.
Frequently asked questions
What does SPN 105 FMI 15 mean on a John Deere engine?
It means the ECU's manifold air temperature (MAT) sensor signal is reading slightly higher than expected for the current operating conditions, while the engine is running. It is a Warning level code, not an active derate.
Will SPN105FMI15 cause a derate?
For this specific fault mode, the ECU response listed is that it tries to maintain proper operating conditions, not that it derates the engine. A separate related code, SPN 105 FMI 0, is tied to a specific manifold air temperature threshold of 120° C (248° F) and has its own control unit response.
How long does the engine need to run before this code can set?
The engine must be running for a minimum of 3 minutes before this DTC can become active.
What are the most common causes of a high manifold air temperature signal?
Common causes include a plugged air filter, a charge air cooler that is plugged externally or internally, a loose fan belt, a damaged fan shroud, exhaust or boost leaks, and a bad MAT sensor, connector, or wiring harness.
Could this code be related to the EGR system?
Yes. Listed causes include a plugged EGR circuit, an EGR system leak, a low-reading EGR flow sensor, and a loose or broken EGR flow sensor venturi bracket. If the engine also has EGR temperature codes set, the EGR valve should be tested for correct operation.
Is it safe to keep operating the machine with this code active?
Since this is a Warning level code without a forced derate listed, the engine will typically keep running, but a persistently high intake air temperature signal should not be ignored. It can point to cooling, airflow, or turbocharger problems that get worse over time.
What should a technician check first for this code?
Start with the basics: air filter condition, charge air cooler cleanliness and airflow, fan belt tension, fan shroud condition, and any visible exhaust or boost leaks, then move to checking the MAT sensor connector, wiring, and sensor itself.