Code Details
| Display code | SPN 102 FMI 1 |
|---|---|
| SPN | 102 |
| FMI | 1 |
| OEM code | None listed |
| Manufacturer | PACCAR |
| 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 | 2026-06-12 |
Plain-English Meaning
The PACCAR MX-13 uses a variable geometry turbocharger to maintain boost pressure matched to the current load. When actual boost falls below the target for sustained periods, the ECM limits fueling to prevent overfueling, reducing power and efficiency. Drivers notice sluggish acceleration and reduced pulling capability. Finding and fixing the boost deficit — whether it is an actuator, a boost leak, or a sensor issue — restores full engine performance.
SPN 102 is Engine Intake Manifold 1 Pressure (boost pressure) in J1939. FMI 1 indicates the measured value is below the normal operating range for the current conditions. On PACCAR MX-13 engines, the EMS commands a VGT vane position to achieve a target boost pressure. If actual boost consistently falls below the target despite full VGT closure effort, the VGT mechanism, turbocharger condition, or a boost leak in the charge air path are the primary suspects. PACCAR ESA provides both commanded and actual boost pressure values, along with VGT actuator position data.
Common Symptoms
- Reduced power under load — particularly on grades and during high-demand acceleration
- Sluggish throttle response compared to normal MX-13 performance
- Possible black or dark exhaust smoke from fuel delivery outpacing available air
- VGT actuator fault code SPN 641 FMI 7 may accompany low boost if the VGT is stuck
- Poor fuel economy from reduced combustion efficiency
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- VGT actuator stuck or not achieving commanded position (carbon buildup or actuator failure)
- Charge air cooler or intercooler boost leak from a cracked hose, clamp, or cooler core
- Boost pressure sensor drift reading below actual pressure
- Turbocharger compressor wheel or bearing wear reducing maximum boost output
- Air filter severely restricted reducing turbocharger inlet flow
First Checks
- Connect PACCAR ESA and compare commanded versus actual boost pressure at various load conditions
- Check all charge air cooler hoses, clamps, and connections for signs of a boost leak
- Inspect the air filter element for restriction — a clogged filter reduces turbocharger inlet flow significantly
- Use ESA to compare VGT actuator commanded and measured position to determine if SPN 641 FMI 7 is a companion fault
- If the sensor seems to be reading low, verify boost pressure with a portable gauge in the intake manifold test port
Can I Keep Driving?
The MX-13 with SPN 102 FMI 1 active will show noticeably reduced power under load. The engine is still operable but at reduced capacity. Identify and correct the boost deficit before extended heavy-haul service.
Related Codes
Related Lookup Pages
Sources
- PACCAR / Kenworth / Peterbilt Service Support — MX Engine Resources PACCAR Inc. · oem · accessed 2026-06-11 · confidence medium
Source: PACCAR Inc., PACCAR / Kenworth / Peterbilt Service Support — MX Engine Resources. 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
Can a charge air cooler boost leak cause SPN 102 FMI 1 on the PACCAR MX-13?
Yes. A boost leak downstream of the turbocharger compressor — from a cracked charge air cooler core, a loose hose clamp, or a deteriorated rubber elbow — reduces the pressure that reaches the intake manifold and the boost sensor. The sensor accurately reads the lower pressure, and the ECM logs the fault because the actual boost is below the target. A boost pressure leak test using compressed air or smoke can locate the source.
Does low boost on the MX-13 damage the turbocharger if the truck continues to operate?
Operating with low boost means the turbocharger is working against an elevated backpressure or delivering less than designed airflow. In the case of a stuck VGT, sustained high exhaust temperatures can accelerate bearing wear. In the case of a boost leak, the turbocharger may operate at higher speeds to compensate, which can also increase wear over time. Identifying and repairing the cause promptly is the best approach.
Does SPN 102 FMI 1 on the MX-13 indicate the VGT actuator has failed?
No. While a stuck VGT is a common cause of low boost, it is not the only cause. Boost leaks, turbocharger wear, sensor issues, and restricted air intake are all capable of producing SPN 102 FMI 1 on the MX-13. PACCAR ESA actuator tests can confirm whether the VGT is contributing, and a visual inspection of the charge air system can rule out boost leaks before committing to turbocharger diagnosis.