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SPN 91 FMI 0 – Accelerator Pedal Circuit Failed High Fault Code (Symptoms, Causes & Fix)

The SPN 91 FMI 0 fault code is a diesel engine fault code indicating an issue with the accelerator pedal circuit, specifically that the circuit has failed high. This diagnostic trouble code suggests that the Engine Control Module (ECM) is detecting a higher than expected voltage signal from the accelerator pedal position sensor.

What SPN 91 FMI 0 Means

The SPN 91 FMI 0 fault code represents a problem in the accelerator pedal position sensor circuit. The ECM interprets this condition as a high voltage signal, which could be due to a malfunctioning sensor, wiring issues, or a problem with the ECM itself. This fault can affect the vehicle's throttle response and overall drivability.

Common Causes of This Fault Code

  • Failed accelerator pedal position sensor
  • Wiring harness damage or short circuits
  • Corroded or damaged connectors
  • ECM signal processing issues
  • Voltage reference faults

Symptoms Drivers May Notice

When the SPN 91 FMI 0 fault code is active, drivers may experience symptoms such as erratic throttle response, reduced engine power, or the vehicle entering a limp mode. These symptoms can vary depending on the severity of the fault and the specific vehicle model.

How Technicians Diagnose This Fault

Diagnosing the SPN 91 FMI 0 fault code involves a systematic approach:

  • Start with a visual inspection of the accelerator pedal position sensor for any physical damage or wear.
  • Check the wiring harness for signs of damage, corrosion, or loose connections.
  • Verify the sensor's power supply and ground circuits using a multimeter.
  • Measure the voltage and resistance at the sensor connector to ensure it is within specifications.
  • Perform a continuity test on the wiring from the sensor to the ECM.
  • Use a diagnostic scan tool to verify the sensor signal and compare it with expected values.

Common Misdiagnosis

Technicians often misdiagnose this fault by replacing the accelerator pedal position sensor without thoroughly checking the wiring or connectors. Another common mistake is assuming a faulty ECM without verifying the integrity of the wiring and connections first.

Can You Keep Driving?

While it may be possible to continue driving with the SPN 91 FMI 0 fault code active, it is not advisable. The fault can lead to reduced engine performance or cause the vehicle to enter a protection mode, potentially resulting in unsafe driving conditions.

Mechanic's Diagnostic Tip

A practical troubleshooting tip is to always check the 5-volt reference circuit when applicable. Many technicians overlook this step, which can lead to unnecessary sensor replacements. Ensure all electrical connections are clean and secure before replacing any components.

Frequently Asked Questions

  • What does SPN 91 FMI 0 indicate? It indicates a high voltage signal from the accelerator pedal position sensor circuit.
  • Can a faulty ECM cause this code? Yes, but it is less common. Always verify wiring and sensor integrity first.
  • Is it safe to drive with this fault code? It is not recommended due to potential drivability issues and safety concerns.

Other FMI Codes for SPN 91