Code Details
| Display code | SPN 100 FMI 1 |
|---|---|
| SPN | 100 |
| FMI | 1 |
| OEM code | None listed |
| Manufacturer | GM |
| System | Engine �?lubrication |
| Component | Engine oil pressure / oil pump |
| Source address | Unknown or not applicable |
| Severity | stop safely |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-11 |
Plain-English Meaning
The Duramax L5P's engine bearings, turbocharger, and internal components all depend on adequate oil pressure for lubrication and cooling. When pressure falls below the minimum threshold, critical damage can occur within minutes of continued operation. This fault requires immediate engine shutdown and investigation. On GM Sierra 4500/5500 and Express 4500 trucks with the 6.6L L5P, the oil pressure sensor is at the engine block and feeds the PCM. GDS2 monitors oil pressure sensor data in real time. The L5P uses variable displacement oil pump technology on some model year applications, which means the oil pressure at idle varies with engine temperature and load in a different pattern than a fixed-displacement pump. GDS2 service data includes the expected pressure range at idle and various RPM points for the specific model year, making it the authoritative reference for sensor plausibility checks.
SPN 100 FMI 1 is Engine Oil Pressure below normal. On the GM Duramax L5P ECM, oil pressure is monitored from the main gallery sensor. A reading below the minimum threshold at the current engine speed and temperature triggers the engine protection strategy. GM scan tools (GDS2, Tech 2) or an advanced OBD2 reader can confirm the actual oil pressure reading and compare it against spec.
Common Symptoms
- Reduced Engine Power or oil pressure warning message on the gauge cluster
- Oil pressure gauge reading low or in the warning zone
- Possible unusual engine noise if oil starvation has progressed
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Low oil level from an oil leak or extended oil consumption
- Oil pump failure
- Oil pressure relief valve stuck open
- Wrong oil viscosity
- Severe internal bearing wear
- Oil pressure sensor fault reading low
First Checks
- Stop the engine and check oil level immediately
- Inspect for visible external oil leaks under the truck
- After confirming oil level is correct, use a GM scan tool to monitor live oil pressure at idle and at 1500 RPM
- Compare scan tool reading to a mechanical gauge for sensor accuracy verification if the reading seems questionable
- Connect GDS2 and compare oil pressure reading at idle and operating RPM to the specified range for the model year
- Verify the oil level is at full mark on the dipstick before any further diagnosis
Can I Keep Driving?
Stop the engine immediately. Continued operation with confirmed low oil pressure risks irreversible engine damage.
Related Codes
Related Lookup Pages
Sources
- GM Trucks Service Support — Duramax Diesel Resources General Motors LLC · oem · accessed 2026-06-11 · confidence medium
Source: General Motors LLC, GM Trucks Service Support — Duramax Diesel 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
What oil specification does the GM Duramax L5P require?
The Duramax L5P requires engine oil meeting the dexos D specification (a diesel-specific formulation). The recommended viscosity is typically SAE 0W-20 or SAE 5W-30 depending on the model year and ambient temperature. Using the correct dexos D oil is important for DPF regen compatibility and proper oil pressure maintenance. Check the owner's manual or the oil cap for the specific requirement.
Is the oil pump on the GM Duramax L5P known to fail at a particular mileage?
The L5P oil pump is not commonly cited as a specific high-failure-rate component at predictable mileages. Oil pump failures are generally associated with insufficient maintenance �?extended oil change intervals, using incorrect oil viscosity, or running with chronic low oil level. Normal maintenance intervals and using the correct oil specification support long pump service life.
Can the Duramax L5P oil life monitoring system account for oil viscosity degradation that causes low pressure?
The GM Oil Life Monitor (OLM) calculates oil change intervals based on engine operating conditions �?temperature, load, and cycles. It does not directly measure oil pressure or viscosity. If the oil is severely degraded due to fuel dilution from DPF regen cycles or extended change intervals, actual oil pressure can drop before the OLM recommends a change. Monitoring oil pressure alongside the OLM is worthwhile in high-demand applications.