John Deere Engines SPN157FMI4 Fault Code: Fuel Rail Pressure Signal Out of Range Low
Also called High Pressure Fuel Signal Out of Range Low, High-Pressure Fuel Signal Out of Range Low
Fuel Rail Pressure Signal Out of Range Low · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 157 FMI 4 sets when the fuel rail pressure sensor signal voltage to the ECU drops below the sensor's low voltage specification, indicating a pressure lower than is physically possible in the fuel rail. The alarm level is STOP (WARNING on redundant ECU applications), and the ECU derates the engine to 50% of full power while forcing the high-pressure fuel pump to a default pressure of 200 MPa (2000 bar / 29,000 psi), ignoring the actual sensor feedback.
High severity. The alarm level is listed as STOP, and the ECU responds by derating engine power to 50% of full power and running the high-pressure pump on a fixed default pressure instead of real sensor feedback. This is a significant power and fuel-system control loss, though redundant ECU applications only trigger a WARNING level alarm instead.
What does John Deere Engines error code SPN157FMI4 mean?
SPN 157 FMI 4 means the ECU sees a fuel rail pressure sensor signal voltage that corresponds to a pressure lower than what is physically possible in the fuel rail. In other words, the sensor is reporting a value the ECU knows can't be real, so it flags the input as out of range low.
Because the ECU can no longer trust the actual rail pressure reading, it stops using sensor feedback and instead commands the high-pressure fuel pump to a fixed default pressure of 200 MPa (2000 bar / 29,000 psi). At the same time it derates the engine down to 50% of full power to protect the fuel system and engine while running in this degraded, open-loop mode.
This code is tied to the same troubleshooting sequence as SPN 3509 FMI 4, and technicians are directed to check SPN 3509 FMI 4 first before diagnosing SPN 157 FMI 4.
What triggers a John Deere Engines SPN157FMI4 code?
The DTC is displayed whenever the ignition is on and the fault condition is active: the fuel rail pressure sensor signal voltage to the ECU corresponds to a rail pressure that is lower than what is physically possible.
Common causes of SPN157FMI4
- Bad terminals or connector at the fuel rail pressure (FRP) sensor
- Bad terminals or connector at the ECU connector
- Bad fuel rail pressure sensor
- Open or short (including short to the signal wire) in the harness, or open/high resistance in the return or supply wires
- Mispin in the harness
- Bad ECU software
- Bad ECU
How to troubleshoot John Deere Engines SPN157FMI4: first checks
- Follow the troubleshooting sequence in order: check SPN 3509 FMI 4 first, then move to SPN 157 FMI 4 diagnostics.
- Inspect the fuel rail pressure sensor connector and terminals for corrosion, looseness, or damage, and do the same at the ECU connector.
- Check the wiring harness between the FRP sensor and ECU for opens, shorts (including shorts to the signal wire), high resistance in the supply or return wires, and any mispinned connections.
- Test or substitute the fuel rail pressure sensor if wiring and connectors check out, since a bad sensor is a listed cause.
- If wiring and sensor both check good, suspect ECU-side issues, including bad ECU software or a bad ECU itself.
How the code clears
No separate clearing step is listed. Since the alarm is active whenever the ignition is on and the fault condition is present, the code should clear once the underlying wiring, connector, sensor, or ECU issue is repaired and the fault condition is no longer active. Confirm repairs by verifying normal fuel rail pressure sensor readings return before returning the machine to full duty.
Frequently asked questions
What does SPN 157 FMI 4 mean on a John Deere engine?
It means the ECU is reading a fuel rail pressure sensor signal voltage that corresponds to a pressure lower than what is physically possible in the fuel rail. The ECU treats this as an out-of-range-low signal fault.
Why does the engine lose power when this code is active?
Because the alarm level is STOP, the ECU derates the engine to 50% of full power. It also stops trusting the fuel rail pressure sensor and instead runs the high-pressure fuel pump at a fixed default pressure of 200 MPa (2000 bar / 29,000 psi).
Is it safe to keep operating with SPN 157 FMI 4 active?
The engine will run in a derated, open-loop fuel pressure mode rather than shutting down completely, but the STOP alarm level and forced default pressure mean this should be diagnosed and repaired promptly rather than ignored.
Does this code always cause a full shutdown?
No. The alarm level is STOP on standard applications but only WARNING on redundant ECU applications, so the exact response depends on the machine's ECU configuration.
What should I check first when troubleshooting SPN 157 FMI 4?
Follow the listed troubleshooting sequence: check SPN 3509 FMI 4 first, then proceed to SPN 157 FMI 4. After that, inspect the fuel rail pressure sensor connector, ECU connector, and harness wiring before considering sensor or ECU replacement.
Can a bad connector alone cause this fault?
Yes. Bad terminals or connectors at either the fuel rail pressure sensor or the ECU are listed as possible causes, along with harness opens, shorts, high resistance, or mispins.
Could this be an ECU problem instead of a sensor problem?
It's possible. Bad ECU software and a bad ECU itself are both listed as possible causes if the sensor and wiring test out normal.