What is SPN 1188 FMI 5 & How to Solve It?

What is SPN 1188 FMI 5:

SPN 1188 relates to the Fuel Rail Pressure Sensor, and FMI 5 means the ECM is detecting a low current signal, which often points to an open circuit or disconnected sensor.

This fault prevents the ECM from accurately measuring fuel pressure, which can affect performance, fuel economy, and emissions control.

‍

Why This Happens

• Disconnected or broken fuel pressure sensor.
• Damaged wiring or corroded connector.
• Open circuit between ECM and sensor.
• Faulty sensor unable to send signal.
• ECM signal interpretation fault.

‍

How to Fix It

1. Inspect the sensor connector and make sure it’s seated properly.
2. Check the wiring harness for cuts or insulation damage.
3. Use a multimeter to check for continuity and voltage.
4. Replace the fuel pressure sensor if the circuit is open.
5. Clear the code and confirm pressure readings in diagnostics.

‍

How to Avoid It Before It Happens

1. Inspect pressure sensors and wiring during regular services.
2. Use weatherproof grease on connectors to prevent corrosion.
3. Train techs to test sensors at signs of poor performance.
4. Keep diagnostic logs of fuel pressure trends.

‍