Throttle Position Sensor - Voltage Above Normal (Open/Short to High)
The CAT-CID91-FMI3 (Caterpillar) diesel fault code means: Throttle Position Sensor - Voltage Above Normal (Open/Short to High). This is a serious severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- intermediate
- Estimated cost
- $150-$500
Down with a CAT fault on the road?
Get connected with a verified mobile diesel mechanic near you. Verified diesel & reefer techs, launching on the freight corridor.
Find a mobile mechanic →A $30 car code reader can't do diesel. The HD7000 reads full-system codes and does parked DPF regen, idle/speed-limit, and service resets from the cab — on everything from a 6.7 Cummins/Power Stroke/Duramax pickup to Class-8 trucks (Detroit, Paccar, CAT, Volvo, Mack, International).
Full-system 6/9/16-pin diesel scan tool for Cummins, Paccar, CAT, Detroit and more — plug-and-play, no subscription. A cheaper way to read heavy-duty codes a basic OBD2 scanner skips entirely.
Affiliate links — we earn a commission at no extra cost to you.
Common Symptoms
- Check Engine Light
- Sensor reads pegged high or low on CAT ET
- Associated systems may derate or default
Probable Causes (Ranked by Likelihood)
- Open circuit in signal wire or unplugged connector Very Likely
- Sensor internally failed open Likely
- Corroded or backed-out connector pin Likely
- Signal wire shorted to sensor supply Possible
Frequently Asked Questions
What does CAT code CID91-FMI3 mean?
CAT code CID91-FMI3 (Throttle Position Sensor - Voltage Above Normal (Open/Short to High)) is a serious-severity fault on Caterpillar on-highway diesel engines. CID 91 is the Throttle Position Sensor, measuring accelerator pedal position. FMI 3 (Voltage Above Normal (Open/Short to High)) indicates the specific fault mode. Use CAT ET to confirm before replacing parts. Diagnose with CAT ET (Electronic Technician) software.
Can I drive my truck with CAT code CID91-FMI3?
Short distances may be acceptable, but running long with this fault risks progressive damage or forced derate. Address promptly.
How much does it cost to fix CAT CID91-FMI3?
Typical repair is $150-$500. Sensor / wiring fixes fall at the low end; injector, HEUI pump, turbo, or aftertreatment work falls at the high end. CAT dealer labor often requires CAT ET for calibration and parameter programming.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
Connect CAT ET and confirm the CID and FMI is active. Note the reported sensor reading.
Disconnect the sensor connector and verify reference voltage at the supply pin key-on.
Jumper signal to return at the connector; if the value swings to the opposite extreme on ET, the sensor is bad.
If no swing, ohm signal wire from connector back to ECM pin; repair open or replace sensor as indicated.
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J1939-73Application Layer: Diagnostics (defines the SPN/FMI fault-identifier framework)
Commonly Affected Vehicles
- Freightliner Classic XL with CAT C15
- Peterbilt 335 with CAT C7
- Peterbilt 386 with CAT C15
- Kenworth T800 with CAT C15
- Western Star 5900 with CAT C15
- Peterbilt 389 with CAT C15
- Peterbilt 387 with CAT C15
- Kenworth T470 with CAT C9
- Kenworth T800 with CAT C13
- Peterbilt 386 with CAT C13
- Thomas / Bluebird school bus with CAT C7
- Peterbilt 387 with CAT C13
- Peterbilt 340 with CAT C9
- Peterbilt 379 with CAT C15
- Kenworth T370 with CAT C7
- Kenworth T660 with CAT C13
- International 9400i with CAT C15
- Kenworth W900 with CAT C15
- Freightliner Columbia with CAT C13
- International 9200i with CAT C13
- International 4300 with CAT C7
- Western Star 4900 with CAT C15
- Freightliner M2 106 with CAT C7
- IC Bus shuttle with CAT C7
- International 9200i with CAT C15
- Kenworth T2000 with CAT C15
Related Codes
Explore More
Was this helpful?
Send this to whoever is fixing the truck — your tech, or the person asking what the fault means.