Freightliner SPN 110 FMI 5: Engine Coolant Temperature Diagnosis
SPN 110 FMI 5 (FMI 5) — Engine Coolant Temperature 1 — Current Below Normal or Open Circuit
Quick Answer
On Freightliner, SPN 110 FMI 5 is a Engine Coolant Temperature fault (Current Below Normal or Open Circuit). Prove wiring/live data first; do not parts-cannon the component.
Overview: Freightliner SPN 110 FMI 5
On Freightliner, SPN 110 FMI 5 is a Engine Coolant Temperature fault (Current Below Normal or Open Circuit). Prove wiring/live data first; do not parts-cannon the component. This guide covers symptoms, root causes, live-data checks, and misdiagnoses for Freightliner platforms.
Repair Snapshot
Time
1 - 3 Hours
Difficulty
Intermediate
Parts Cost
$50 - $800
Dealer Labor
$350+
Tools Required
- Detroit DDDL8
- Noregon JPRO
- Multimeter
What SPN 110 FMI 5 Means
SPN 110 FMI 5 on Freightliner means Engine Coolant Temperature 1 — Current Below Normal or Open Circuit. Confirm Compare ECT to infrared at thermostat housing with Detroit DDDL8 / Noregon JPRO before replacing the engine coolant temperature.
Symptoms Drivers Notice
- Check-engine / amber warning lamp illuminated.
- Soft power, unstable idle, or poor response when engine coolant temperature data is irrational.
- Live data for engine coolant temperature fails rationality vs mechanical gauge or partner sensors.
- Codes may return immediately after clearing if root cause remains.
Most Likely Root Causes
Common Misdiagnoses (Don't Waste Parts)
Why it happens:
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Why it happens:
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Why it happens:
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Master Tech Commentary
Mechanic's Notes
Shop tip (Freightliner): For SPN 110 FMI 5, prove Compare ECT to infrared at thermostat housing before quoting the Engine Coolant Temperature. Common false path is replacing the sensor when the harness or reference circuit is the failure.
Step-by-Step Diagnostic Procedure
- Step 1: Connect Detroit DDDL8 or Noregon JPRO and record SPN 110 FMI 5 with freeze-frame load/temp.
- Step 2: Inspect harness and connector at the engine coolant temperature for chafe, corrosion, and bent pins.
- Step 3: Verify 5V reference / ground / signal integrity with a multimeter where applicable.
- Step 4: Compare ECT to infrared at thermostat housing
- Step 5: Repair the proven fault, clear only after repair, and verify under the same conditions as freeze-frame.
Live Data & Freeze-Frame Tips
Log Engine Coolant Temperature with Detroit DDDL8 under freeze-frame conditions. Compare ECT to infrared at thermostat housing. Compare to a mechanical gauge when pressure/temperature related.
When to Limp In vs Tow
Drive carefully to a shop if lamps are warning-only and power remains controllable; tow if power loss is severe.
Related Fault Codes
Frequently Asked Questions
What does Freightliner SPN 110 FMI 5 mean?
It indicates a Engine Coolant Temperature fault: Current Below Normal or Open Circuit. Confirm with live data and wiring tests before parts replacement.
Can SPN 110 cause a derate?
It can contribute to limp behavior if the ECM loses trust in critical data, especially when paired with other faults.
What tools diagnose this best?
Detroit DDDL8 and Noregon JPRO, plus a quality multimeter and mechanical gauges for pressure/temperature checks.
Should I clear the code first?
No. Capture freeze-frame and the full stack first. Clear only after the repair and verification.
More Freightliner codes on this system
- Freightliner SPN 111 FMI 1 — Engine Coolant Level Sensor
- Freightliner SPN 110 FMI 3 — Engine Coolant Temperature Sensor (ECT) Circuit
- Freightliner SPN 641 FMI 7 — VGT Actuator
- Freightliner SPN 3464 FMI 10 — Aftertreatment SCR Catalyst
- Freightliner SPN 91 FMI 2 — Accelerator Pedal Position Sensor
- Freightliner SPN 102 FMI 3 — Boost Pressure Sensor Circuit
- Freightliner SPN 4094 FMI 16 — DPF Soot Load
- Freightliner SPN 190 FMI 0 — Engine Speed Sensor Circuit
Guides that go deeper
- SPN 1569 FMI 31: Engine Protection Shutdown and Safe Recovery Steps [2026 Diagnostic Guide]
SPN 1569 FMI 31 means engine protection shutdown is active—not the root fault. Read stacked codes, verify oil and coolant, then reset only after the trigger is fixed.
- SPN 3031 DEF Tank Temperature Fault: Heater, Sensor, or Wiring
SPN 3031 points at DEF tank temperature strategy faults. Confirm heaters, sensor rationality, and harness chafe before replacing the tank assembly.
- Detroit DDDL Basics: Finding the Root Code Behind a Derate
Use Detroit DDDL the right way: separate root SPN/FMI faults from inducement result codes, read derate stage data, and stop replacing parts on guesses.