Intake Air Temperature Sensor - Voltage Above Normal (Open/Short to High)
The CAT-CID172-FMI3 (Caterpillar) diesel fault code means: Intake Air Temperature Sensor - Voltage Above Normal (Open/Short to High). This is a moderate severity code.
Unverified. We could not confirm this code's definition against freely available manufacturer documentation, so treat the meaning, severity and fix guidance on this page as unconfirmed. Check it against the manufacturer's service information for your exact model and serial range before acting on it. This page is kept out of search engines for that reason, and we are working through this family manual by manual.
- Keep driving?
- Short distances only
- DIY difficulty
- intermediate
- Estimated cost
- $150-$500
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View pilot availability →What Are the Symptoms of CAT-CID172-FMI3?
- Check Engine Light
- Sensor reads pegged high or low on CAT ET
- Associated systems may derate or default
What Causes CAT-CID172-FMI3? (Most Likely First)
- 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
Can I Still Drive with CAT-CID172-FMI3?
Short distances only. CAT-CID172-FMI3 is rated moderate severity. Keep trips short and get it diagnosed soon rather than waiting for symptoms to worsen.
Frequently Asked Questions
What does CAT code CID172-FMI3 mean?
CAT code CID172-FMI3 (Intake Air Temperature Sensor - Voltage Above Normal (Open/Short to High)) is a moderate-severity fault on Caterpillar on-highway diesel engines. CID 172 is the Intake Air Temperature Sensor, measuring intake air temperature. 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 CID172-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 CID172-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
How Do You Diagnose CAT-CID172-FMI3?
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)
Which Vehicles Commonly Get CAT-CID172-FMI3?
- 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
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