EGR Temperature Sensor - Voltage Below Normal (Short to Low)
What does CAT-CID412-FMI4 mean?
The CAT-CID412-FMI4 (Caterpillar) diesel fault code means: EGR Temperature Sensor - Voltage Below Normal (Short to Low). This is a moderate severity code.
Common Symptoms
- Check Engine Light
- Sensor reads opposite extreme on CAT ET
- Possible derate or false operating condition
Probable Causes (Ranked by Likelihood)
- Signal wire shorted to ground Very Likely
- Sensor internally shorted Likely
- Moisture or contamination in connector Possible
Step-by-Step Diagnostic Procedure
Confirm active fault in CAT ET.
Disconnect sensor; if the reading flips to the opposite extreme, the sensor is internally shorted.
If reading stays pinned, measure signal wire to ground with sensor unplugged; a short confirms harness damage.
Repair harness chafe or replace sensor as determined.
Frequently Asked Questions
What does CAT code CID412-FMI4 mean?
CAT code CID412-FMI4 (EGR Temperature Sensor - Voltage Below Normal (Short to Low)) is a moderate-severity fault on Caterpillar on-highway diesel engines. CID 412 is the EGR Temperature Sensor, measuring EGR gas temperature after cooler. FMI 4 (Voltage Below Normal (Short to Low)) 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 CID412-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 CID412-FMI4?
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.