Code Details
| Display code | SPN 105 FMI 0 |
|---|---|
| SPN | 105 |
| FMI | 0 |
| OEM code | None listed |
| Manufacturer | Cummins |
| System | Engine �?charge air cooling |
| Component | Charge air cooler (CAC) / intercooler / intake manifold temperature sensor |
| Source address | Unknown or not applicable |
| Severity | medium |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-11 |
Plain-English Meaning
The charge air cooler cools the air compressed by the turbocharger before it enters the engine. Cooler air is denser, providing more oxygen per volume for combustion. When intake temperature rises above the normal range, it indicates the charge air cooler is not cooling the air adequately. This reduces power and efficiency and increases the thermal load on the engine.
SPN 105 is Engine Intake Manifold Temperature in J1939. FMI 0 indicates the measured temperature is above the normal operating range. On Cummins CM2350, the intake manifold temperature sensor provides feedback used for combustion optimization and as a secondary indicator of charge air cooler performance. High intake temperature can be caused by a blocked CAC, a CAC internal leak (combustion gases bypassing into the air side), or the sensor measuring ambient temperature after a cold soak (less common). Insite displays the live intake air temperature and boost pressure simultaneously to correlate charge air condition.
Common Symptoms
- Reduced power under load
- Possible increase in NOx-related aftertreatment faults over time
- Engine runs warmer generally if charge air cooling is significantly compromised
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Charge air cooler (CAC) fins plugged with road debris reducing airflow
- CAC internal leak allowing hot exhaust gases from a failed EGR-air mixing fault to enter
- Intake air temperature sensor fault reading artificially high
- Ambient temperature is very high and the truck is under maximum load (occasional condition, not a component fault)
First Checks
- Inspect the external CAC fins for debris blockage and clean if necessary
- Check for a CAC internal leak by pressurizing the charge air system and inspecting the CAC for internal combustion gas contamination
- Connect Cummins Insite and monitor intake manifold temperature alongside charge air cooler inlet temperature to quantify the delta
- Verify the intake air temperature sensor reading against actual ambient temperature when the engine is cold
Can I Keep Driving?
The engine will reduce fueling to protect combustion quality with elevated intake temperatures, resulting in reduced power. Cleaning the CAC or addressing the internal leak restores normal performance.
Related Codes
Related Lookup Pages
Sources
- Cummins INSITE Service Tool — Public Reference Documentation Cummins Inc. · oem · accessed 2026-06-11 · confidence medium
Source: Cummins Inc., Cummins INSITE Service Tool — Public Reference Documentation. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - QuickServe Online Cummins Inc. · oem · accessed 2026-05-05 · confidence medium
Source: Cummins Inc., QuickServe Online. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - 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
FAQ
How do I clean the charge air cooler fins on a truck without removing it?
For external debris on the CAC fins, a careful wash with a low-pressure water stream from the front of the truck �?or an air blower directed from the engine side outward �?can dislodge most road debris and insects. Avoid high-pressure washing directly on the fins, which can flatten the delicate aluminum fins and reduce airflow capacity.
Can a failed CAC cause SPN 105 FMI 0 and also affect fuel economy on the Cummins ISX15?
Yes. A severely plugged or leaking CAC reduces both charge air density and combustion efficiency. The driver may notice reduced power and slightly higher fuel consumption as the engine's fuel management system tries to compensate for the degraded air charge quality.
Is the charge air cooler on the ISX15 part of the engine or the truck chassis?
The charge air cooler (intercooler) is a chassis component provided by the truck OEM, not the engine manufacturer. It is typically mounted in the radiator stack at the front of the truck. Replacement typically involves the truck OEM part number rather than a Cummins part number, and the specific location varies between cab and chassis types.