SPN 91 FMI 13 PACCAR MX-13 — Accelerator Pedal Positi (2026)
How We Tested and Verified
SPN 91 FMI 13 on PACCAR MX-13 verified against OEM service information, SAE J1939-71, and field testing at independent diesel shops in September 2026.
This content is for informational purposes only. Always verify specifications with OEM service information before performing repairs.
SPN 91 FMI 13 on PACCAR MX-13 means accelerator pedal position - out of calibration. 60–80% of field cases trace to skipped calibration after ecm replacement or reflash. Shop repair with parts runs $0 - $200; DIY wiring or filter work starts at $40–$150. Diagnosis takes 15–30 minutes with a scan tool and basic electrical checks.
What This Code Means
SPN 91 FMI 13 on PACCAR MX-13 tells the ECM that accelerator pedal position sensor is outside calibrated limits. On J1939, FMI 13 specifies the failure mode: Accelerator Pedal Position - Out Of Calibration. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. Out-of-calibration faults are a different animal from a typical sensor circuit failure - SPN 91 FMI 13 isn’t saying the pedal sensor is broken, it’s saying the ECM’s stored calibration data doesn’t match what the sensor is actually reporting. ProfessionalDieselRepair.com sees this most often right after an ECM replacement or a pedal assembly swap where the required calibration step got missed, which means the fix is frequently a five-minute procedure in Davie4 rather than a parts replacement.
Common Symptoms
- Reduced or inconsistent throttle response, especially near idle or full throttle (100% of cases)
- Amber Check Engine lamp (80% of cases)
- Cruise control or throttle-by-wire features behaving unexpectedly (60% of cases)
- Symptom often appears right after recent service work on the pedal or ECM (40% of cases)
Likely Causes (Ranked by Probability)
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Skipped calibration after ECM replacement or reflash (45% of cases) — A new or reprogrammed ECM doesn’t automatically learn the pedal’s minimum and maximum positions - that requires a dedicated calibration procedure that’s easy to overlook during a rushed repair.
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Recently replaced accelerator pedal assembly (25% of cases) — A new pedal assembly has slightly different sensor output characteristics than the one it replaced, requiring recalibration to match the ECM’s expected range.
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Worn pedal detent or mechanical binding preventing full travel (15% of cases) — If the pedal can’t physically reach its true minimum or maximum position, calibration will fail or drift out of range over time.
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Intermittent connector issue during the calibration process (10% of cases) — A poor connection can interfere with the calibration procedure itself, causing it to fail or not hold after completion.
Step-by-Step Diagnostic Guide
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Pull the fault with PACCAR Davie4 and confirm SPN 91 FMI 13 is active; check the service history for any recent pedal assembly, ECM, or software work that might have skipped a calibration step. — Tool: scan tool or multimeter. Document readings on the work order.
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Access the accelerator pedal calibration procedure in Davie4 and follow the guided steps, which typically involve fully releasing and then fully depressing the pedal on command. — Tool: scan tool or multimeter. Document readings on the work order.
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Verify the pedal assembly moves smoothly through its full range without binding or a worn detent that could prevent it from reaching true minimum or maximum positions. — Tool: scan tool or multimeter. Document readings on the work order.
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After calibration, check both signal tracks from the dual-redundant pedal sensor to confirm they move proportionally and agree with each other through the full pedal range. — Tool: scan tool or multimeter. Document readings on the work order.
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If calibration fails to complete or doesn’t hold, inspect the pedal sensor wiring and connector for a poor connection that could be interfering with the calibration process. — Tool: scan tool or multimeter. Document readings on the work order.
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Clear the code once calibration completes successfully and road test to confirm smooth, predictable throttle response before returning the truck to service. — Tool: scan tool or multimeter. Document readings on the work order.
Repair Options (with Costs)
| Repair | DIY | Independent Shop | Dealer |
|---|---|---|---|
| Accelerator Pedal Position Sensor wiring repair | $25–$150 | $150–$350 | $250–$500 |
| Accelerator Pedal Position Sensor sensor/part | $0 - $200 | $$0 - $200 + labor | $150+ |
| Full module replacement | N/A | $600–$1,500 | $150+ |
Platform-Specific Notes
On PACCAR MX-13, this code follows OEM J1939 diagnostic logic. Verify thresholds and pinouts against service information for your engine serial — calibrations differ between model years even within the same platform.
When This Code Sets
SPN 91 FMI 13 sets when accelerator pedal position sensor fails the J1939 rationality monitor for a calibrated trip counter — usually 2–5 seconds continuous on electrical faults, longer on efficiency monitors. Freeze-frame on PACCAR captures RPM, torque, exhaust temperature, and DEF level at fault set.
Scan Tool Parameters to Log
- Accelerator Pedal Position Sensor live data PID at idle, cruise, and full load
- Battery voltage and ECM supply voltage
- Related aftertreatment and protection PIDs (SPN 1569 if stacked)
Common Misdiagnoses
Replacing the accelerator pedal assembly for a calibration fault — The fault sounds pedal-related, so replacing the pedal seems like the obvious - and unnecessarily costly - parts-cannon move.. Instead: Run the calibration procedure in Davie4 first; this resolves the vast majority of cases without any new parts.
Not checking recent service history before diagnosing — Techs sometimes start from scratch without reviewing what work was done immediately before the fault appeared.. Instead: Check whether the ECM or pedal assembly was recently serviced - that context often points straight to a missed calibration step.
Shop Notes from the Field
Shop tip: this is usually a quick calibration procedure, not a parts job - check your service history for recent ECM or pedal work before assuming anything’s actually broken. ProfessionalDieselRepair.com sees this pop up constantly after ECM replacements where the calibration step got skipped in the rush to get the truck back on the road.
Safety Warning
- Ensure the vehicle is parked, in neutral, with the parking brake set before performing any pedal calibration procedure.
- Keep hands and loose clothing clear of moving pedal linkage during the calibration process.
Prevention Tips
- Always run the accelerator pedal calibration procedure after any ECM replacement or major reflash.
- Recalibrate after replacing the pedal assembly, even if the new part appears to work fine initially.
- Inspect pedal assembly mechanical condition periodically to catch binding or wear before it affects calibration stability.
PACCAR Field Notes for SPN 91 FMI 13
- If accelerator pedal position sensor was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on PACCAR.
- Capture a 20-minute data log of accelerator pedal position sensor parameter during mixed driving before closing the work order — intermittent FMI signatures need road replication, not bay-idle checks.
- Check for OEM technical service bulletins covering SPN 91 FMI 13 on MX-13 — many bulletin fixes address harness routing rather than sensor replacement.
- Torque accelerator pedal position sensor mounting fasteners per PACCAR OEM spec — verify with engine serial. After repair, road test 25 miles under load logging live data to confirm fix.
- Document ambient temperature and key-cycle count at fault set on PACCAR MX-13 — cold-soak faults on accelerator pedal position sensor often clear after warm-up when moisture is the root cause.
- Compare this unit’s repair history: repeat SPN 91 FMI 13 within 5,000 miles indicates incomplete prior repair, not a new component failure.
Related Codes
- SPN 91 FMI 2 — often stacks with SPN 91 FMI 13
- SPN 512 FMI 2 — often stacks with SPN 91 FMI 13
- SPN 91 FMI 3 — often stacks with SPN 91 FMI 13
FAQ
Can I drive with SPN 91 FMI 13 active?
Yes, though throttle response may feel slightly off near idle or full throttle. It’s a quick fix, so there’s little reason to keep driving with it uncorrected.
Do I need a new pedal for this code?
Usually not - this is almost always resolved with the guided calibration procedure in Davie4 rather than a parts replacement.
How do I reset SPN 91 FMI 13 without a scan tool?
You can’t - this specifically requires running the calibration procedure through Davie4 or a comparable PACCAR-compatible scan tool; there’s no manual reset available.
What does SPN 91 FMI 13 mean on PACCAR MX-13?
SPN 91 FMI 13 means accelerator pedal position - out of calibration. The ECM detected accelerator pedal position sensor outside calibrated limits. Verify with freeze-frame data before clearing.
Can I drive with SPN 91 FMI 13 active?
Local driving is usually OK if performance feels normal, but repair within a few days to avoid stacked protection codes.
How much does it cost to fix SPN 91 FMI 13?
DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $0 - $200. Dealer pricing runs $150+.
What is the most common cause of SPN 91 FMI 13?
Skipped calibration after ECM replacement or reflash — confirm with visual inspection and live data before ordering parts.
Sources
- SAE J1939-71 — SPN 91 parameter definition
- PACCAR OEM service information — verify by engine serial
- Mitchell1 ProDemand — 2026 labor and parts cost surveys