Detroit Diesel SPN 105 FMI 5: Intake Manifold Temperature Diagnosis
SPN 105 FMI 5 (FMI 5) — Engine Intake Manifold 1 Temperature — Current Below Normal or Open Circuit
Quick Answer
On Detroit Diesel, SPN 105 FMI 5 is a Intake Manifold Temperature fault (Current Below Normal or Open Circuit). Prove wiring/live data first; do not parts-cannon the component.
Overview: Detroit Diesel SPN 105 FMI 5
On Detroit Diesel, SPN 105 FMI 5 is a Intake Manifold 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 Detroit Diesel 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 105 FMI 5 Means
SPN 105 FMI 5 on Detroit Diesel means Engine Intake Manifold 1 Temperature — Current Below Normal or Open Circuit. Confirm Check IAT vs ambient; inspect connector resistance with Detroit DDDL8 / Noregon JPRO before replacing the intake manifold temperature.
Symptoms Drivers Notice
- Check-engine / amber warning lamp illuminated.
- Soft power, unstable idle, or poor response when intake manifold temperature data is irrational.
- Live data for intake manifold 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 (Detroit Diesel): For SPN 105 FMI 5, prove Check IAT vs ambient; inspect connector resistance before quoting the Intake Manifold 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 105 FMI 5 with freeze-frame load/temp.
- Step 2: Inspect harness and connector at the intake manifold temperature for chafe, corrosion, and bent pins.
- Step 3: Verify 5V reference / ground / signal integrity with a multimeter where applicable.
- Step 4: Check IAT vs ambient; inspect connector resistance
- 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 Intake Manifold Temperature with Detroit DDDL8 under freeze-frame conditions. Check IAT vs ambient; inspect connector resistance. 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 Detroit Diesel SPN 105 FMI 5 mean?
It indicates a Intake Manifold Temperature fault: Current Below Normal or Open Circuit. Confirm with live data and wiring tests before parts replacement.
Can SPN 105 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 Detroit Diesel codes on this system
- Detroit Diesel SPN 102 FMI 16 — Turbocharger Boost Pressure
- Detroit Diesel SPN 2789 FMI 14 — VGT Actuator Position
- Detroit Diesel SPN 105 FMI 3 — Intake Manifold Temperature Sensor
- Detroit Diesel SPN 641 FMI 3 — Variable Geometry Turbocharger Actuator 1
- Detroit Diesel SPN 3226 FMI 13 — Outlet NOx Sensor
- Detroit Diesel SPN 2659 FMI 18 — Turbocharger
- Detroit Diesel SPN 4364 FMI 18 — Aftertreatment SCR Catalyst
- Detroit Diesel SPN 91 FMI 2 — Accelerator Pedal Position Sensor
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.
- 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.
- 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.