Detroit DD13 EPA07 (2007-09) Fault Code: SPN 91 FMI 2 (CPC) – Accelerator Pedal Position Erratic Data

Detroit DD13 EPA07 (2007–09) – SPN 91 FMI 2 (CPC): Accelerator Pedal Position Erratic Data

Fault Code Overview

Fault Code Description

SPN 91 FMI 2 is set by the Common Powertrain Controller (CPC) when the accelerator pedal position (APP) sensor signal is erratic, inconsistent, or does not correlate with expected values. Unlike FMI 3 (failed high) or FMI 4 (failed low), FMI 2 indicates the signal is present but unstable — jumping, dropping out intermittently, or not tracking correctly through pedal travel. This is typically caused by a failing pedal assembly, intermittent wiring, or a poor connector connection.

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

Probable Causes

1. Accelerator pedal assembly (failing or worn APP sensor).
2. Accelerator pedal harness/connector fault (intermittent connection, corrosion, or chafed wiring).

Symptoms

• Amber warning lamp illuminated on the dash
• SPN 91 FMI 2 logged in the CPC fault memory
• Erratic or unpredictable throttle response
• Engine surging, hesitation, or unexpected RPM changes
• Accelerator pedal position signal jumping or dropping in DDDL live data
• Possible engine derate

Diagnostic Steps

1. Connect diagnostic software (Detroit Diesel DiagnosticLink / DDDL) and confirm the active or inactive fault code SPN 91 FMI 2 in the CPC. Monitor the accelerator pedal position live data while slowly depressing and releasing the pedal — look for any signal drops, jumps, or dead spots.
2. Inspect the accelerator pedal connector — check for corrosion, moisture, bent or pushed-back pins, and loose fit. Wiggle the connector while monitoring live data to check for intermittent signal loss. Clean and reseat the connector. Apply dielectric grease if needed.
3. Inspect the harness — trace the accelerator pedal wiring from the pedal to the CPC connector. Look for chafing, pinched wires, cracked insulation, or areas where the harness may flex and cause intermittent contact. Repair as needed.
4. Test the accelerator pedal assembly — measure voltage output across the APP sensor terminals through the full pedal travel range while monitoring for any signal irregularities. Compare to the specification in the Detroit DD13 service manual. Replace the pedal assembly if the output is erratic or has dead spots.
5. Check connector pin tension — inspect the CPC harness connector pins for spread or damaged terminals that may cause intermittent contact. Repair or replace terminals as needed.
6. Clear the fault code and perform a road test. Monitor the accelerator pedal position signal in DDDL live data through full pedal travel to confirm the signal is smooth and consistent.
7. 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 4 – Accelerator Pedal Position Circuit Failed Low
• 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.