PACCAR · Accelerator Pedal Position SensorMedium

PACCAR SPN 91 FMI 13: Recalibrating the Accelerator Pedal Position Sensor

SPN 91 FMI 13 (FMI 13) — Accelerator Pedal Position - Out Of Calibration

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Quick Answer

SPN 91 FMI 13 on PACCAR MX-13 engines means the accelerator pedal position sensor is out of calibration. It's a medium-severity fault that's usually a quick fix with Davie4's guided calibration procedure - most cases don't require any new parts.

Overview: PACCAR SPN 91 FMI 13

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.

Repair Snapshot

Time

0.5 - 1.5 Hours

Difficulty

Beginner

Parts Cost

$0 - $200

Dealer Labor

$150+

Tools Required

  • PACCAR Davie4
  • Diesel Laptops Scan Tool
  • Multimeter

What SPN 91 FMI 13 Means

SPN 91 FMI 13 means the ECM has determined the accelerator pedal position sensor is out of calibration - its output doesn't align with the expected range for a fully released or fully depressed pedal. On a PACCAR MX-13, this is a medium-severity fault that commonly shows up after an ECM replacement, a pedal assembly swap, or a software update that didn't complete a required calibration step.

Symptoms Drivers Notice

  • Reduced or inconsistent throttle response, especially near idle or full throttle
  • Amber Check Engine lamp
  • Cruise control or throttle-by-wire features behaving unexpectedly
  • Symptom often appears right after recent service work on the pedal or ECM

Most Likely Root Causes

Skipped calibration after ECM replacement or reflash

Common

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.

Recently replaced accelerator pedal assembly

Common

A new pedal assembly has slightly different sensor output characteristics than the one it replaced, requiring recalibration to match the ECM's expected range.

Worn pedal detent or mechanical binding preventing full travel

Occasional

If the pedal can't physically reach its true minimum or maximum position, calibration will fail or drift out of range over time.

Intermittent connector issue during the calibration process

Rare

A poor connection can interfere with the calibration procedure itself, causing it to fail or not hold after completion.

Common Misdiagnoses (Don't Waste Parts)

Replacing the accelerator pedal assembly for a calibration fault

Why it happens: The fault sounds pedal-related, so replacing the pedal seems like the obvious - and unnecessarily costly - parts-cannon move.

Do this 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

Why it happens: Techs sometimes start from scratch without reviewing what work was done immediately before the fault appeared.

Do this instead: Check whether the ECM or pedal assembly was recently serviced - that context often points straight to a missed calibration step.

Master Tech Commentary

Mechanic's Notes

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.

Step-by-Step Diagnostic Procedure

  1. Step 1: 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.
  2. Step 2: 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.
  3. Step 3: 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.
  4. Step 4: 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.
  5. Step 5: 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.
  6. Step 6: Clear the code once calibration completes successfully and road test to confirm smooth, predictable throttle response before returning the truck to service.

Live Data & Freeze-Frame Tips

During the Davie4 calibration procedure, watch both pedal sensor signal tracks in real time as you slowly move the pedal through its full range. Both tracks should move smoothly and proportionally with no sudden jumps - any irregularity here suggests a mechanical or wiring issue that needs to be resolved before calibration will hold.

Safety Warnings

  • 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.

When to Limp In vs Tow

Towing is never necessary for this fault - the truck remains safely drivable, and the calibration procedure is a quick in-shop fix that doesn't require roadside intervention.

Prevention Tips for Fleets & Owner-Operators

  • 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.

Related Fault Codes

SPN 91 FMI 2

Accelerator pedal position data erratic - a distinct fault indicating a live signal quality problem rather than a stored calibration mismatch.

SPN 512 FMI 2

Driver's demand torque data erratic - can result if the pedal calibration issue is significant enough to affect the calculated torque request.

SPN 91 FMI 3

Accelerator pedal position sensor circuit voltage above normal - a genuine electrical fault, different from this calibration-specific code.

Frequently Asked Questions

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.

Why did this code appear after my ECM was replaced?

A new or reflashed ECM needs to learn the pedal's minimum and maximum position values through a dedicated calibration step - if that step was skipped, this fault will set.

Will this code cause an engine derate?

No, this specific calibration fault doesn't trigger a power derate - it primarily causes inconsistent or slightly inaccurate throttle response until recalibrated.

How long does the calibration procedure take?

Typically just a few minutes - it involves following on-screen prompts in Davie4 to fully release and fully depress the pedal on command.