Engine Coolant Temperature Sensor - Voltage Low / Short to Ground
The CAT-CID2-FMI4 (Caterpillar) diesel fault code means: Engine Coolant Temperature Sensor - Voltage Low / Short to Ground. 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-$400
Down with a CAT fault on the road?
We are building a network of verified mobile diesel and reefer technicians along the freight corridor. It is not live yet — no one can be dispatched to you today. You can see where the pilot is launching and register interest.
View pilot availability →What Are the Symptoms of CAT-CID2-FMI4?
- Check Engine Light
- ECT reads pegged high (typically 260°F+) on CAT ET
- Fan runs constantly
- Possible derate from false overheat indication
What Causes CAT-CID2-FMI4? (Most Likely First)
- Signal wire shorted to ground or return Very Likely
- ECT sensor internally shorted Likely
- Moisture / coolant intrusion in sensor connector Possible
Can I Still Drive with CAT-CID2-FMI4?
Short distances only. CAT-CID2-FMI4 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 CID2-FMI4 mean?
CAT code CID2-FMI4 (Engine Coolant Temperature Sensor - Voltage Low / Short to Ground) is a moderate-severity fault on Caterpillar on-highway diesel engines. CID 2 FMI 4 is ECT signal voltage too low, almost always a shorted wire or bad sensor making the ECM think the engine is dangerously hot. Diagnose with CAT ET (Electronic Technician) software.
Can I drive my truck with CAT code CID2-FMI4?
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 CID2-FMI4?
Typical repair is $150-$400. 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-CID2-FMI4?
Confirm fault with CAT ET; unplug sensor — if reading flips to -40°F, wire is OK, sensor is shorted.
Measure resistance sensor signal to ground with connector off; should be open. Short = harness issue.
Inspect connector for coolant intrusion; dielectric grease and repair.
Replace ECT sensor if proven shorted internally.
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-CID2-FMI4?
- 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
Explore More
Was this helpful?
Send this to whoever is fixing the truck — your tech, or the person asking what the fault means.