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SPN 157 — Injector Metering Rail Pressure #1

Updated: 2026-11-10

Safe to driveTo the nearest safe stop

J1939 code SPN 157. Below — how the fault is worded at the factory by Cummins ISB, DAF, Detroit Diesel, Dongfeng, Foton, Isuzu, KAMAZ, MAZ, Renault Trucks, SITRAK, YaMZ and ZF AS-Tronic, and what the second half of the code (FMI) means in the standard.

How to check it yourself

The fuel pressure sensor sits on the end of the common rail. Three-wire: 5 V reference, ground and signal. The ECU regulates the pressure from it, so this code almost always comes with loss of power or the engine stopping.

What it should read

Reference voltage at the connector5.0 V ± 0.25
Signal with the engine offabout 0.5 V
Pressure for startingusually not less than 200…300 bar — check against the factory data

Check order

  1. FMI 3, 4 (electrical): unplug the connector, inspect the contacts, and with the ignition on measure the 5 V reference. With the engine off the sensor should show close to zero pressure: if it shows hundreds of bar — the sensor is at fault.
  2. FMI 1, 17, 18 (pressure low): fuel first — level, coarse and fine filters, transfer pump. Air in the clear hose or bubbles in the sedimenter — an air leak on the suction side.
  3. Check the leak-off from the injectors: disconnect the returns and compare how much each one returns on cranking or at idle. If one returns noticeably more than the others — that injector is pulling the rail pressure down.
  4. Check the pressure regulating valve on the high-pressure pump and the rail's pressure relief valve (the rail has a drain pipe): a leak from the relief valve with the engine running — it has opened or is faulty.
  5. FMI 0, 16 (pressure high): pressure regulating valve on the high-pressure pump, clogged drain from the rail.

Common causes — from most to least frequent

  1. Clogged fuel filters, air leak on the suction side.
  2. Worn injector with excessive leak-off.
  3. Pressure regulating valve on the high-pressure pump.
  4. Rail pressure relief valve.
  5. Connector or the pressure sensor itself.
  6. Worn high-pressure pump.

Cummins ISBDAFDetroit DieselDongfengFotonIsuzuKAMAZMAZRenault TrucksSITRAKYaMZZF AS-Tronic

Cummins ISB 6.7 engine

FMI 0Injector metering rail 1 pressure: above normal range, most severe
FMI 3Injector metering rail 1 pressure sensor circuit voltage high
FMI 4Injector metering rail 1 pressure sensor circuit voltage low
FMI 7Injector metering rail 1 pressure, mechanical system not responding
FMI 15Injector metering rail 1 pressure high, least severe
FMI 16Injector metering rail 1 pressure high, moderately severe
FMI 18Injector metering rail 1 pressure low, moderately severe

DAF

FMI 0Fuel pressure F648 pressure too high
FMI 2Fuel pressure F648 invalid or missing signal
FMI 3Fuel pressure F648 short to power supply at ECU pin A29
FMI 4Fuel pressure F648 short to ground at ECU pin A29
FMI 16Fuel pressure F648 pressure too high (actual above setpoint)
FMI 18Fuel pressure F648 pressure too low (actual more than 100 bar below setpoint)

Detroit Diesel

FMI 18DD15: Fault of the Fuel Rail Pressure Sensor, Wiring or Quantity Control Valve; DD8: Fuel Rail Pressure Too High

Dongfeng

FMI 0High-pressure fuel rail safety valve open
FMI 2Fuel pressure signal stuck (not changing)
FMI 3Short circuit to power supply of the fuel pressure sensor. Scan tool code: P0193. Effect: Engine speed is limited.
FMI 4Short circuit to ground or open circuit of the fuel pressure sensor. Scan tool code: P0192. Effect: Engine speed is limited to 1400 rpm.
FMI 16Fuel pressure too high. Scan tool code: P0190. Effect: Power limited, the engine runs unevenly.
FMI 18Fuel pressure too low. Scan tool code: P0190. Effect: Power limited, the engine runs unevenly.

Foton

FMI 18Insufficient fuel rail pressure. Scan tool code: P0190. Effect: Power limited, the engine runs unevenly.

Isuzu

FMI 0Common rail pressure fault (1st stage) (P0088)
FMI 2Common rail pressure fault (Excessive pressure feed in pump) (P0089)
FMI 3Common rail pressure sensor fault (high voltage fault) (P0193)
FMI 4Common rail pressure sensor fault (low voltage fault) (P0192)

KAMAZ engine (J1939)

FMI 3Rail fuel pressure sensor
FMI 4Rail fuel pressure sensor
FMI 15Rail pressure sensor: signal offset out of tolerance
FMI 17Rail pressure sensor: signal offset out of tolerance

MAZ

FMI 3Fuel rail pressure sensor circuit fault - Voltage above allowed. Blink code: 1-3-3. Power will be reduced. Repair: Check the rail pressure sensor and its wiring.
FMI 4Fuel rail pressure sensor circuit fault - Voltage below allowed. Blink code: 1-3-3. Power will be reduced. Repair: Check the rail pressure sensor and its wiring.
FMI 15Fuel rail pressure sensor circuit fault - Signal value above the maximum allowed. Blink code: 1-3-3. Power will be reduced. Repair: Check the rail pressure sensor and its wiring.
FMI 17Fuel rail pressure sensor circuit fault - Signal value below the minimum allowed. Blink code: 1-3-3. Power will be reduced. Repair: Check the rail pressure sensor and its wiring.

Renault Trucks

FMI 0Selector cylinder sensor drifts from its position. Repair: Switch the ignition off, switch it on again and repeat the test. If the fault persists, replace the control unit.

SITRAK

FMI 3Rail pressure sensor voltage above the upper limit. Scan tool code: P0193. Effect: Engine speed is limited.
FMI 4Rail pressure sensor voltage below the lower limit. Scan tool code: P0192. Effect: Engine speed is limited to 1400 rpm.
FMI 7Engine failed to start: no pressure built up in the rail. Scan tool code: P016E. Effect: Power limited, the engine runs unevenly.
FMI 15Rail pressure sensor drift: voltage too high. Scan tool code: P0191. Effect: Engine speed is limited.
FMI 16Rail pressure correction value at the maximum limit. Scan tool code: P0190. Effect: Power limited, the engine runs unevenly.
FMI 17Rail pressure sensor drift: voltage too high. Scan tool code: P0191. Effect: Engine speed is limited.
FMI 18Rail pressure correction value at the minimum limit. Scan tool code: P0190. Effect: Power limited, the engine runs unevenly.
FMI 22Positive rail pressure deviation during cold start and rapid heat-up. Scan tool code: P016E. Effect: Power limited, the engine runs unevenly.
FMI 23Negative rail pressure deviation during cold start and rapid heat-up. Scan tool code: P016E. Effect: Power limited, the engine runs unevenly.
FMI 27Zero delivery not reached at the lower set value limit of the metering unit governor. Scan tool code: P016E. Effect: Power limited, the engine runs unevenly.
FMI 28Zero delivery not reached at the lower set value limit of the metering unit governor. Scan tool code: P016E. Effect: Power limited, the engine runs unevenly.

YaMZ

FMI 3Fuel rail pressure sensor circuit fault (Voltage above allowable limit). Blink code: 1-3-3. Power will be reduced. Repair: Check the rail pressure sensor and its wiring.
FMI 4Fuel rail pressure sensor circuit fault (Voltage below allowable limit). Blink code: 1-3-3. Power will be reduced. Repair: Check the rail pressure sensor and its wiring.
FMI 15Fuel rail pressure sensor circuit fault (Signal value above maximum allowable limit). Blink code: 1-3-3. Power will be reduced. Repair: Check the rail pressure sensor and its wiring.
FMI 17Fuel rail pressure sensor circuit fault (Signal value below minimum allowable limit). Blink code: 1-3-3. Power will be reduced. Repair: Check the rail pressure sensor and its wiring.

ZF AS-Tronic gearbox

FMI is per the block maker's own table, not the J1939 table below.

FMI 0Main gear engagement sensor signal stays in the selected position.

What FMI means in J1939

SPN 157 FMI 0157/0 · 157.0data above normal range (most severe level)
SPN 157 FMI 2157/2 · 157.2data erratic or intermittent
SPN 157 FMI 3157/3 · 157.3voltage above normal or shorted high
SPN 157 FMI 4157/4 · 157.4voltage below normal or shorted to ground
SPN 157 FMI 7157/7 · 157.7mechanical system not responding
SPN 157 FMI 15157/15 · 157.15above normal — low severity
SPN 157 FMI 16157/16 · 157.16above normal — moderate severity
SPN 157 FMI 17157/17 · 157.17below normal — low severity
SPN 157 FMI 18157/18 · 157.18below normal — moderate severity

Can I keep driving

Safe to drive. Below — how much time you have and what happens if you keep going.

What happens if you keep driving

Time you have: To the nearest safe stop

Fuel is not arriving in the right amount or at the right pressure. It shows up first on climbs and under load.

You will most likely stall out on the road, and may not restart on the shoulder. A clogged filter or water in the tank you can nurse to a shop; a failing injection pump you cannot.

This is an electrical fault: an open, a short or a bad contact in the sensor circuit. The value it measures is most likely fine. You can drive. But until the circuit is repaired this system runs blind and cannot warn you about a real failure.

That said, the manufacturer flags this code as critical — if in doubt, it is safer to stop and check on the spot.

What to check on the spot

Check the fuel filter and water trap, drain the water. In cold weather, suspect fuel waxing.

Which codes follow

If the value really did go out of range, rather than a sensor circuit being broken, these normally light up after it:

They are not fixed separately — they go out together with this one. The list is deliberately short: only the links the reference is sure about.

Nearby: fuel

Makes with this code

KAMAZMAZYaMZSITRAKDongfengFotonDAFRenault TrucksIsuzuCummins ISBDetroit Diesel

Related problems

Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.