CAT Engine E100 Fault Code: Low Engine Oil Pressure Warning

What does CAT Engine error code E100 mean?

E100 is CAT's low engine oil pressure warning code, used across the C12, C15, C16, and C27 engines. The ECM watches oil pressure through a dedicated sensor and compares it against pressure maps programmed into the ECM. These setpoints cannot be changed by the customer.

When pressure falls into the low-pressure region for the required time, the ECM logs the event, lights the warning lamp in the cab, and pushes the code to the display and to any connected diagnostic scan tool. On the J1939 data link the same event shows up as SPN 100 FMI 01, and on the Cat Data Link it appears as EID 100.

This code is strictly about pressure being too low. It is separate from 100-03 (oil pressure circuit open or shorted to battery) and 100-04 (oil pressure circuit shorted to ground), both of which must be inactive for E100 to set. That distinction matters because it tells you the ECM believes the sensor circuit itself is electrically healthy and the pressure reading is real.

What triggers a CAT Engine E100 code?

The ECM sets E100 when several conditions are true together: the engine has been running for at least 10 seconds, with that delay starting once engine speed is within 50 rpm of low idle to allow oil pressure to build after startup. Oil pressure must then sit inside the low-pressure region for at least 5 seconds (some versions reference a trip point held for 2 seconds). At the same time, 100-03 (open or short to battery) and 100-04 (short to ground) must not be active. One version simply requires engine speed above 0 rpm for 10 seconds before the ECM evaluates the warning at all. The ECM resets the warning once pressure rises back above the low-pressure trip point, with one version specifying that pressure must climb 21 kPa (3 psi) above the trip point and stay there for 20 seconds before the warning clears.

Common causes of E100

• Low engine oil level, which reduces the pump's ability to maintain pressure
• Air leakage into the lubrication system, which can cause pressure to fluctuate or drop
• A damaged or worn engine oil pump that can no longer generate adequate pressure
• A general problem with the engine lubrication system beyond the pump, such as blocked passages or excessive bearing clearance
• A faulty engine oil pressure sensor sending a false low reading even though actual pressure is fine

How to troubleshoot CAT Engine E100: first checks

1. 1Stop and shut down the engine as soon as it's safe to do so. Running with confirmed low oil pressure risks serious internal damage.
2. 2Check the engine oil level on the dipstick once the machine is on level ground and the engine has been off long enough for oil to settle. Top off if low.
3. 3Inspect for visible oil leaks around the pan, filter, cooler lines, and fittings that could point to air getting pulled into the system or oil loss.
4. 4Check the oil pressure sensor's wiring and connector for corrosion, looseness, or damage, since a sensor or circuit fault can mimic a real pressure problem.
5. 5Confirm the code is a true low pressure warning and not 100-03 or 100-04, since those point to a wiring problem on the sensor circuit rather than actual oil pressure.
6. 6If the level and wiring check out, have the oil pump and lubrication system inspected by a qualified technician before returning the machine to service.

How the code clears

The ECM resets the warning automatically once oil pressure rises back above the low-pressure trip point. One version specifies this recovery requires pressure to climb 21 kPa (3 psi) above the trip point and hold there for 20 seconds before the warning clears. No separate manual reset procedure is listed for this code; fixing the underlying cause is what allows the warning to clear on its own.

Affected models and serial ranges

E100 appears in our records across 4 CAT Engine models. Match your machine by model and serial number.