CAT Engine 157 Fault Code: Low Engine Oil Pressure - Warning
Low Engine Oil Pressure - Warning · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 157, SPN 100 FMI 17, means the ECM has detected engine oil pressure in the Level 1 low-pressure range for eight seconds after the engine has run at least ten seconds. It triggers a flashing warning lamp and a 46 flash code, but at this level engine operation is not affected. Related, more severe stages (Level 2, Level 3) bring on power derate or engine shutdown.
Medium severity. At the 360-1 level, engine operation is not affected and this is a warning only. But low oil pressure is a serious mechanical concern, and if pressure drops further the ECM will escalate to derate (360-2) or shutdown (360-3). Treat this as diagnose-now, not ignore-it.
What does CAT Engine error code 157 mean?
CAT fault code 157, SPN 100 FMI 17, is the ECM's low engine oil pressure warning. Engine oil pressure keeps a film of lubrication between moving parts like bearings, camshaft, and crankshaft journals. When pressure drops into a low range the ECM flags it before real damage can occur.
This code corresponds to the 360-1 stage of a three-level oil pressure monitoring system. At 360-1 the engine keeps running normally, the warning lamp flashes, and a 46 flash code plus an E360-1 event code are logged. On the J1939 data link this shows up as SPN 100 FMI 17, which may also display on other connected devices.
If oil pressure continues to fall, the system escalates: Level 2 (SPN 100 FMI 18) triggers a power derate, and Level 3 (SPN 100 FMI 01) triggers an engine shutdown, both only if the corresponding customer programmable parameter (Enable Derate or Enable Shutdown) has been turned on.
What triggers a CAT Engine 157 code?
The ECM sets this code when three conditions are all true: the engine has been running for at least ten seconds, there are no active diagnostic codes for the oil pressure sensor or the atmospheric pressure sensor, and engine oil pressure has been in the Level 1 low-pressure area for eight seconds. The warning is cancelled once oil pressure rises 21 kPa (3 psi) above the set point and stays there for 20 seconds.
Common causes of 157
- Low engine oil level, which reduces the oil pump's ability to maintain pressure
- A failing or degraded oil pressure sensor or its wiring, though the ECM will not set this code if the sensor itself has an active diagnostic code
- A problem with the atmospheric pressure sensor, since an active fault there also blocks this code from setting and can point to a related sensor issue
- Actual low oil pressure from pump wear, a clogged oil filter, or worn bearings reducing system pressure
- Oil viscosity issues, such as using the wrong oil grade or oil that is excessively diluted or degraded
How to troubleshoot CAT Engine 157: first checks
- Check engine oil level on the dipstick with the machine on level ground and the engine off, top off if low
- Inspect the oil filter and oil condition for contamination, sludge, or signs of dilution
- Confirm there are no active diagnostic codes for the oil pressure sensor or atmospheric pressure sensor first, since either one can suppress this code from behaving as expected
- Look at wiring and connectors at the oil pressure sensor for corrosion, looseness, or damage
- Pull up the ECM event log to see whether the code has escalated toward Level 2 or Level 3, which indicates a worsening condition
How the code clears
No separate clearing step is listed beyond the built-in cancellation condition: once oil pressure rises 21 kPa (3 psi) above the set point and holds there for 20 seconds, the warning lamp and active code clear automatically. If the code keeps returning, the underlying oil pressure problem needs to be fixed rather than just waiting for it to clear.
Frequently asked questions
What does CAT fault code 157 mean?
It means the ECM detected engine oil pressure in the Level 1 low range (SPN 100 FMI 17) for eight seconds after the engine had been running for at least ten seconds. It is a warning stage, and engine operation is not affected at this level.
Is it safe to keep operating with code 157 active?
At the 360-1 warning stage, engine operation is not affected, so the machine can keep running. But this is a sign oil pressure is trending low, and if it drops further the ECM can derate power or shut the engine down at higher severity levels, so it should be checked promptly.
Will code 157 cause the engine to derate or shut down?
Not by itself. Code 157 corresponds to the Level 1 warning only, which does not affect engine operation. Derate happens at Level 2 (SPN 100 FMI 18) and shutdown happens at Level 3 (SPN 100 FMI 01), and only if the Enable Derate or Enable Shutdown parameters are turned on.
How does the warning clear on its own?
The ECM cancels the warning once oil pressure rises 21 kPa (3 psi) above the set point and stays there for 20 seconds. No separate manual reset procedure is listed.
What should I check first if I get code 157?
Start with the oil level and oil condition, then check for active codes on the oil pressure sensor or atmospheric pressure sensor, since those can block this code from behaving normally. Also inspect wiring at the oil pressure sensor.
Why does the atmospheric pressure sensor matter for an oil pressure code?
The ECM will not generate this code if there are active diagnostic codes on either the oil pressure sensor or the atmospheric pressure sensor. So a fault on that second sensor can affect whether this warning sets at all.