B2BEmersonEIMS serves commercial, industrial & institutionalcommercial, industrial, healthcare, telecom, hospitality, government & contractor clients.• Engineering-led • SLA-backed • Documented commissioning
Keyboard Shortcuts
The high-pressure fuel rail in the common-rail injection system is not achieving required pressure. Modern diesel engines require very high fuel pressure (1,600-2,000+ bar) for proper atomization. Low rail pressure causes poor combustion, white smoke, hard starting, and significant power loss.
SPN-157 reports fuel injector metering rail pressure (common rail). The FMI (Failure Mode Identifier) shown beside it says how the reading is wrong. FMI meanings follow the SAE J1939 standard used by Cummins and most modern diesel engine controllers.
SPN-157 FMI 1
Rail pressure far below normal (most severe).
Check first: Fuel level, lift pump, blocked fuel filters, air in the fuel.
SPN-157 FMI 18
Rail pressure below normal (moderately severe).
Check first: Fuel filters and water separator, high-pressure pump output, injector leak-off.
SPN-157 FMI 16
Rail pressure above normal (moderately severe).
Check first: Rail pressure control valve and the pressure relief valve.
SPN-157 FMI 2
The rail pressure reading jumps about or does not match engine behaviour.
Check first: The connector on the rail pressure sensor at the end of the common rail — fuel and heat there loosen and corrode it.
SPN-157 FMI 3
The rail pressure sensor is reporting a voltage too high to be real — typically a broken wire or a short to the sensor supply.
Check first: The rail sensor harness where it runs close to the injector lines; it is often damaged when injectors or lines are refitted.
SPN-157 FMI 4
The rail pressure sensor is reporting a voltage too low to be real — typically a short to ground.
Check first: Harness clips near the high-pressure pump and rail; a pinched wire grounding on the block is common after engine work.
Need parts? Call us with your engine or controller model and we will confirm what we can supply and when.Call +254 768 860 665
Low rail pressure is commonly caused by worn injectors leaking fuel back, a failing high-pressure pump, or fuel supply restrictions. An injector leak-back test can identify leaking injectors.
Connect clear tubes to each injector return line and measure fuel collected during cranking. More than 80ml per minute indicates a leaking injector that needs replacement.
Send us the code or alarm and what the generator is doing, and one of our engineers will help you diagnose it.
Search other controller alarms and engine fault codes, with troubleshooting steps, in Generator Oracle.
Launch Generator Oracle →Full diagnostic guide
A fault code names a symptom, not a cause. Our engineers have written the diagnostic sequence they use on site for this class of fault — ranked causes, ordered steps with the reading expected at each one, and the point at which to stop and call someone.
8 diagnostic steps · intermediate · technician
10 diagnostic steps · intermediate · technician
9 diagnostic steps · intermediate · technician