PACCAR SPN 91 FMI 5: Accelerator Pedal Position Diagnosis
SPN 91 FMI 5 (FMI 5) — Accelerator Pedal Position 1 — Current Below Normal or Open Circuit
Quick Answer
On PACCAR, SPN 91 FMI 5 is a Accelerator Pedal Position fault (Current Below Normal or Open Circuit). Prove wiring/live data first; do not parts-cannon the component.
Overview: PACCAR SPN 91 FMI 5
On PACCAR, SPN 91 FMI 5 is a Accelerator Pedal Position fault (Current Below Normal or Open Circuit). Prove wiring/live data first; do not parts-cannon the component. This guide covers symptoms, root causes, live-data checks, and misdiagnoses for PACCAR platforms.
Repair Snapshot
Time
1 - 3 Hours
Difficulty
Intermediate
Parts Cost
$50 - $800
Dealer Labor
$350+
Tools Required
- PACCAR Davie
- Noregon JPRO
- Multimeter
What SPN 91 FMI 5 Means
SPN 91 FMI 5 on PACCAR means Accelerator Pedal Position 1 — Current Below Normal or Open Circuit. Confirm 5V ref and signal swing 0.5-4.5V with PACCAR Davie / Noregon JPRO before replacing the accelerator pedal position.
Symptoms Drivers Notice
- Check-engine / amber warning lamp illuminated.
- Soft power, unstable idle, or poor response when accelerator pedal position data is irrational.
- Live data for accelerator pedal position fails rationality vs mechanical gauge or partner sensors.
- Codes may return immediately after clearing if root cause remains.
Most Likely Root Causes
Common Misdiagnoses (Don't Waste Parts)
Why it happens:
Do this instead:
Why it happens:
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Why it happens:
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Master Tech Commentary
Mechanic's Notes
Shop tip (PACCAR): For SPN 91 FMI 5, prove 5V ref and signal swing 0.5-4.5V before quoting the Accelerator Pedal Position. Common false path is replacing the sensor when the harness or reference circuit is the failure.
Step-by-Step Diagnostic Procedure
- Step 1: Connect PACCAR Davie or Noregon JPRO and record SPN 91 FMI 5 with freeze-frame load/temp.
- Step 2: Inspect harness and connector at the accelerator pedal position for chafe, corrosion, and bent pins.
- Step 3: Verify 5V reference / ground / signal integrity with a multimeter where applicable.
- Step 4: 5V ref and signal swing 0.5-4.5V
- Step 5: Repair the proven fault, clear only after repair, and verify under the same conditions as freeze-frame.
Live Data & Freeze-Frame Tips
Log Accelerator Pedal Position with PACCAR Davie under freeze-frame conditions. 5V ref and signal swing 0.5-4.5V. Compare to a mechanical gauge when pressure/temperature related.
When to Limp In vs Tow
Drive carefully to a shop if lamps are warning-only and power remains controllable; tow if power loss is severe.
Related Fault Codes
Frequently Asked Questions
What does PACCAR SPN 91 FMI 5 mean?
It indicates a Accelerator Pedal Position fault: Current Below Normal or Open Circuit. Confirm with live data and wiring tests before parts replacement.
Can SPN 91 cause a derate?
It can contribute to limp behavior if the ECM loses trust in critical data, especially when paired with other faults.
What tools diagnose this best?
PACCAR Davie and Noregon JPRO, plus a quality multimeter and mechanical gauges for pressure/temperature checks.
Should I clear the code first?
No. Capture freeze-frame and the full stack first. Clear only after the repair and verification.
More PACCAR codes on this system
- Paccar SPN 190 FMI 0 — Engine Speed Sensor Circuit
- PACCAR SPN 100 FMI 1 — Engine Oil Pressure Sensor
- PACCAR SPN 168 FMI 1 — Battery / Charging System Circuit
- PACCAR SPN 3510 FMI 3 — 5-Volt Sensor Supply Voltage 2
- PACCAR SPN 91 FMI 13 — Accelerator Pedal Position Sensor
- Paccar SPN 636 FMI 8 — Crankshaft Position Sensor
- Paccar SPN 1188 FMI 3 — Turbocharger Wastegate Actuator Position Sensor
- PACCAR SPN 1209 FMI 16 — Engine Exhaust Gas Pressure
Guides that go deeper
- SPN 2791 EGR Valve Actuator Fault: Test Before You Replace Parts
SPN 2791 points at EGR valve/actuator control problems. Confirm command vs actual position, 5V reference, and carbon binding before condemning the cooler.
- SPN 1569 FMI 31: Engine Protection Shutdown and Safe Recovery Steps [2026 Diagnostic Guide]
SPN 1569 FMI 31 means engine protection shutdown is active—not the root fault. Read stacked codes, verify oil and coolant, then reset only after the trigger is fixed.
- Detroit DDDL Basics: Finding the Root Code Behind a Derate
Use Detroit DDDL the right way: separate root SPN/FMI faults from inducement result codes, read derate stage data, and stop replacing parts on guesses.