SPN 100: oil pressure has dropped - shut the engine off
Updated: 2026-11-10
In short. With FMI 1 and 18 the oil pressure really is below normal and the engine must be shut off at once: without oil the crankshaft and bearings wear out within minutes. FMI 3 and 4 concern the sensor, but until the pressure is checked with a mechanical gauge, treat it as real.
FMI breakdown
SPN 100 in the J1939 standard is Engine oil pressure.
| FMI | Meaning | What to do |
|---|---|---|
| 1 | Pressure below normal, most severe level (Cummins ISB 6.7: FC 415) | Shut off the engine |
| 18 | Pressure below normal, medium urgency (Cummins ISB 6.7: FC 143) | Do not drive, find the cause |
| 3 | Sensor circuit voltage above normal or short to positive (Cummins FC 135) | Check connector and wiring |
| 4 | Sensor circuit voltage below normal or short to ground (Cummins FC 141) | Check connector and wiring |
FMI 1 and 18 speak of the pressure itself, FMI 3 and 4 of the sensor's electrical circuit.
Can you drive
No. With FMI 1 and 18 shut the engine off at once and do not push on "to the nearest place": oil starvation destroys the crankshaft and bearings within minutes. With FMI 3 and 4 first check whether the sensor is lying by fitting a mechanical gauge.
What the driver does
- Stop and shut off the engine.
- Wait a few minutes and check the oil level on the dipstick on level ground.
- Inspect the engine for oil leaks.
- Level is fine: screw a mechanical gauge in place of the sensor and compare with the dashboard.
- Gauge shows normal: the sensor or wiring is at fault, so inspect the connector and wires. No pressure: do not start the engine, call a tow truck.
When to see a workshop
- pressure is really low with a normal oil level: a clogged pickup screen, a worn oil pump or bearings, fuel or coolant in the oil are possible;
- FMI 3 or 4 repeats after the connector and wiring were checked: sensor and sensor supply line diagnostics are needed.
Questions and answers
Can I drive with SPN 100 FMI 1?
No. Shut the engine off at once: without oil pressure the crankshaft and bearings wear out within minutes.
How is FMI 18 different from FMI 1?
Both mean pressure below normal. FMI 1 is the most severe level, FMI 18 medium urgency; in both cases you must not drive and must find the cause.
What do FMI 3 and 4 mean for SPN 100?
A fault in the sensor circuit (voltage above normal or short to positive, below normal or short to ground), not proof that the oil is low.
How do I confirm the pressure is really low?
Screw a mechanical gauge in place of the sensor and compare the reading with the dashboard.
Code pages on the site
- SPN 100 - oil pressure, all makes
- SPN 110 - coolant temperature
- SPN 97 - water in fuel
Checked against manufacturer manuals and tables; the same facts as in our videos and articles. The decision to drive remains with the driver.
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