Code Details
| Display code | SPN 102 FMI 1 |
|---|---|
| SPN | 102 |
| FMI | 1 |
| OEM code | None listed |
| Manufacturer | Cummins |
| System | Engine �?turbocharger / charge air |
| Component | Turbocharger / charge air cooler / boost pressure 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 ISX15 and X15 rely on turbocharger boost to efficiently combust fuel at high power levels. The turbocharger's variable geometry vanes are controlled to build the required pressure for each operating condition. When actual boost falls below the target, the ECM limits fuel delivery to prevent overfueling, resulting in reduced power and efficiency.
SPN 102 is Engine Intake Manifold 1 Pressure (boost pressure). FMI 1 indicates the measured value is below the normal operating range for the current conditions. On Cummins CM2350 ISX15/X15 engines, the turbocharger VGT system commands a vane position to achieve a target boost. If actual boost is consistently below target despite maximum VGT vane closure effort, the VGT mechanism, turbocharger wheel condition, or charge air cooler leak are the primary suspects. Insite provides both commanded and actual boost pressure values.
Common Symptoms
- Reduced power under load
- Sluggish response to throttle
- Possible black smoke from overfueling relative to available air
- Increased turbocharger response time
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- VGT actuator fault preventing vanes from closing to build boost
- Turbocharger compressor wheel damage or bearing wear
- Charge air cooler or intercooler boost leak
- Intake air leak between the turbocharger outlet and engine intake
- Boost pressure sensor drift reading low
- Air filter severely restricted reducing turbocharger inlet flow
First Checks
- Connect Cummins Insite and compare commanded vs. actual boost pressure at various load points
- Inspect the charge air cooler hoses and clamps for loose connections or cracks
- Check air filter restriction indicator �?a severely clogged filter reduces turbocharger inlet flow and limits achievable boost
- Use Insite to check VGT actuator position vs. commanded position (companion code SPN 641 FMI 7 would indicate a VGT mechanical fault)
- If the sensor reading seems incorrect, verify boost pressure with a portable gauge in the intake manifold test port
Can I Keep Driving?
Reduced power and responsiveness, especially under load. The engine is still operable but at reduced performance. Identify and repair the cause before extended heavy-load operation.
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
What is the typical idle and full-load boost pressure for a Cummins ISX15 or X15?
At idle, a healthy ISX15 or X15 produces minimal boost �?typically less than 5 psi. At full load and rated speed, peak boost can reach 45 to 55 psi depending on the engine rating and VGT calibration. Cummins Insite provides the commanded boost target for every operating condition, allowing direct comparison to the actual sensor reading.
Can a boost leak between the turbocharger and the intake manifold cause SPN 102 FMI 1?
Yes. A significant boost leak �?from a cracked charge air cooler, loose hose clamp, or damaged intercooler pipe �?will reduce the pressure that reaches the intake manifold sensor. The sensor will read accurately, but the measured pressure will be lower than the target because air is escaping before it reaches the sensor. A smoke test or boost pressure leak test can locate this type of leak.
Does a worn turbocharger compressor wheel always cause SPN 102 FMI 1 on the ISX15?
Not always. Minor compressor wheel damage or bearing wear may reduce maximum boost slightly but may not produce a fault code under light load conditions. SPN 102 FMI 1 typically sets when the actual pressure is measurably below the target across multiple operating conditions, indicating a significant boost deficit rather than a minor efficiency loss.