Detroit DD13 EPA07 (2007-09) Fault Code: SPN 91 FMI 4 (CPC) – Accelerator Pedal Position Circuit Failed Low

Detroit DD13 EPA07 (2007–09) – SPN 91 FMI 4 (CPC): Accelerator Pedal Position Circuit Failed Low

Fault Code Overview

Fault Code Description

SPN 91 FMI 4 is set by the Common Powertrain Controller (CPC) when the accelerator pedal position (APP) sensor signal voltage falls below the minimum expected threshold. The CPC monitors the APP sensor to determine driver throttle demand. A failed-low signal indicates a short to ground in the signal circuit, an open sensor supply, or a failed accelerator pedal assembly.

Note: Please see the step-by-step troubleshooting procedures for this specific code.

Probable Causes

1. Accelerator pedal assembly (failed APP sensor).
2. Accelerator pedal harness/connector fault.

Symptoms

• Amber warning lamp illuminated on the dash
• SPN 91 FMI 4 logged in the CPC fault memory
• Engine may default to idle or limited throttle response
• Accelerator pedal position reading at or near 0% in DDDL live data
• Possible engine derate

Diagnostic Steps

1. Connect diagnostic software (Detroit Diesel DiagnosticLink / DDDL) and confirm the active fault code SPN 91 FMI 4 in the CPC. Check live data for the accelerator pedal position percentage.
2. Inspect the accelerator pedal connector — check for corrosion, moisture, bent or pushed-back pins, and loose fit. Clean and reseat the connector. Apply dielectric grease if needed.
3. Measure the 5V sensor supply — with the key on and pedal connected, back-probe the supply pin at the pedal connector. A reading significantly below 5V or 0V indicates an open or shorted supply circuit. Trace and repair the wiring.
4. Disconnect the accelerator pedal and measure signal wire voltage — with the pedal disconnected and key on, the signal wire should read near 5V (pulled up by the CPC). A reading near 0V confirms a short to ground in the signal wire. Locate and repair the short.
5. Test the accelerator pedal assembly — measure resistance or voltage output across the APP sensor terminals through the full pedal travel range. Compare to the specification in the Detroit DD13 service manual. Replace the pedal assembly if out of spec.
6. Inspect the harness — trace the accelerator pedal wiring from the pedal to the CPC connector. Look for chafing, pinched wires, or insulation damage. Repair as needed.
7. Clear the fault code and perform a key cycle. Monitor the accelerator pedal position signal in DDDL live data through full pedal travel to confirm the circuit is operating within the normal range.
8. Replace the CPC only if all wiring, connector, and pedal assembly checks pass and the fault persists.

Related Fault Codes

• SPN 91 FMI 3 – Accelerator Pedal Position Circuit Failed High
• SPN 91 FMI 2 – Accelerator Pedal Position Signal Erratic
• SPN 29 – Accelerator Pedal Position 2
• SPN 974 – Remote Accelerator Pedal Position

Recommended Tools

• Detroit Diesel DiagnosticLink (DDDL) software
• Digital multimeter
• Wiring diagram for Detroit DD13 EPA07
• RP1210-compliant diagnostic adapter (Nexiq USB Link, Noregon DLA+, etc.)

Always refer to the official Detroit Diesel service documentation and wiring diagrams for your specific vehicle configuration before performing repairs.