EGR Valve Position Sensor - Voltage Low
The CAT-CID1079-FMI4 (Caterpillar) diesel fault code means: EGR Valve Position Sensor - Voltage Low. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- advanced
- Estimated cost
- $600-$5500
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Common Symptoms
- Check Engine Light
- Black smoke, especially under load
- Low power or derate
- Poor fuel economy
- Rough idle / misfire
- Coolant loss (if EGR cooler is failing)
Probable Causes (Ranked by Likelihood)
- EGR valve seized or carboned up Very Likely
- EGR actuator motor or position feedback failed Likely
- Wiring or connector issue at EGR valve Likely
- EGR cooler cracked/leaking coolant (common ACERT failure) Possible
- EGR venturi tube cracked Possible
- Calibration lost after battery or ECM power-down Less Likely
Frequently Asked Questions
What does CAT CID1079-FMI4 mean?
CAT code CID1079-FMI4 (EGR Valve Position Sensor - Voltage Low) is a moderate-severity EGR fault on C13 and C15 ACERT engines. EGR valve position sensor shorted to ground. ACERT engines are notorious for EGR cooler failures that leak coolant into the intake.
Is the EGR cooler failing a common issue on ACERT engines?
Yes. The C13 and C15 ACERT EGR cooler is a known weak spot. Symptoms include coolant loss with no visible external leak, white smoke at startup, and oil contamination. Delete / bypass kits are popular in some markets but may be illegal on-road in many jurisdictions.
How much to fix CAT CID1079-FMI4?
EGR valve cleaning is $300-$500 labor. EGR valve replacement is $800-$1500. EGR cooler replacement is $2500-$5500 depending on engine access. EGR venturi tube is $600-$1200.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
Read active and logged faults with CAT ET; note EGR valve commanded vs actual position.
Command EGR valve through its range in CAT ET; watch position feedback.
Remove EGR valve and inspect for carbon loading; clean or replace as required.
Pressure-test EGR cooler for coolant-side leaks (very common ACERT failure).
Inspect EGR venturi tube for cracks (tube runs hot and is prone to fatigue).
Perform EGR re-learn in CAT ET after any replacement.
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
- Kenworth T800 with CAT C15
- Kenworth W900 with CAT C15
- Kenworth T2000 with CAT C15
- Peterbilt 379 with CAT C15
- Peterbilt 389 with CAT C15
- Peterbilt 386 with CAT C15
- Peterbilt 387 with CAT C15
- Freightliner Classic XL with CAT C15
- International 9200i with CAT C15
- International 9400i with CAT C15
- Western Star 4900 with CAT C15
- Western Star 5900 with CAT C15
- Kenworth T800 with CAT C13
- Kenworth T660 with CAT C13
- Peterbilt 386 with CAT C13
- Peterbilt 387 with CAT C13
- Freightliner Columbia with CAT C13
- International 9200i with CAT C13
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