Mack · Intake Manifold 1 Temperature Sensor (IMT)High

Mack SPN 105 FMI 16: High Intake Manifold 1 Temperature

SPN 105 FMI 16 (FMI 16) — Intake Manifold 1 Temperature - Data Valid But Above Normal Operating Range - Moderately Severe Level

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Quick Answer

SPN 105 FMI 16 on Mack engines means intake manifold air temperature is above the normal range with valid sensor data. Charge-air cooler leaks, EGR cooler failure, or turbo issues can cause derate. Compare IMT to ambient and CAC outlet temps in ServiceMaxx before replacing the sensor.

Overview: Mack SPN 105 FMI 16

Intake temperature faults on Mack powerplants usually trace to something heating the air charge, not a bad wire. ProfessionalDieselRepair.com walks through charge-air and EGR checks first because FMI 16 tells you the ECM trusts the temperature reading.

Repair Snapshot

Time

2 - 5 Hours

Difficulty

Advanced

Parts Cost

$150 - $2,800

Dealer Labor

$650+

Tools Required

  • ServiceMaxx
  • Noregon JPRO
  • Boost Leak Tester
  • Multimeter

What SPN 105 FMI 16 Means

SPN 105 FMI 16 on Mack MP7, MP8, and MP10 engines signals intake manifold air temperature above the calibrated limit with valid sensor data. Charge-air cooling failure, EGR cooler leakage, or a stuck VGT can drive IMT high enough to trigger torque derate and protect the turbo from overspeed. Compare IMT against ambient and charge-air cooler outlet temperature in ServiceMaxx.

Symptoms Drivers Notice

  • Amber or red check engine lamp with active SPN 105 FMI 16
  • High intake manifold temperature reading in ServiceMaxx live data
  • Noticeable power loss or derate climbing grades
  • Elevated coolant consumption if EGR cooler is leaking internally
  • Hot air from charge-air plumbing or damaged CAC boots

Most Likely Root Causes

Charge-air cooler leak or clogged CAC

Common

Leaks reduce cooling efficiency and raise manifold air temperature under boost.

EGR cooler internal leak heating intake charge

Common

Coolant entering the EGR path superheats intake air and often pairs with coolant loss.

Failed intake manifold temperature sensor reading high

Occasional

A drifting NTC can report high temperature when the actual charge air is normal.

Common Misdiagnoses (Don't Waste Parts)

Replacing the IMT sensor before pressure-testing the CAC

Why it happens: Sensors are quick to order and install.

Do this instead: Parts-cannon sensor swaps miss boost leaks. Pressure-test to 30 psi and compare CAC outlet to IMT in live data.

Ignoring coolant loss with a high IMT code

Why it happens: Drivers focus on power loss, not the overflow tank.

Do this instead: Pressure-test the cooling system and inspect EGR cooler passages when coolant disappears without external leaks.

Master Tech Commentary

Mechanic's Notes

ProfessionalDieselRepair.com sees Mack SPN 105 FMI 16 after a blown charge-air boot that was taped instead of replaced. IMT tracks what the air actually feels going into the manifold; fix the heat source before blaming the sensor.

Step-by-Step Diagnostic Procedure

  1. Step 1: Log IMT, ambient air temp, and charge-air cooler outlet temp in ServiceMaxx during a loaded pull.
  2. Step 2: Inspect charge-air cooler fins, boots, and clamps for leaks; a boost leak raises compressor outlet temperature.
  3. Step 3: Pressure-test the CAC to 30 psi and listen for leaks at hose ends and tank seams.
  4. Step 4: Check EGR cooler for white exhaust smoke and coolant loss; a leaking EGR cooler heats intake air with hot coolant vapor.
  5. Step 5: Test the IMT sensor resistance at room temperature; typical NTC spec is 2.5-4.5k ohms at 77F. Replace only if out of spec and CAC/EGR are healthy.

Professional service / OEM-level scan tools are recommended before clearing this fault for good.

Live Data & Freeze-Frame Tips

In ServiceMaxx, plot IMT against turbo boost and vehicle speed on a grade. IMT rising faster than ambient with moderate boost points to CAC efficiency loss; IMT high at idle suggests EGR cooler or sensor drift.

Safety Warnings

  • Charge-air pipes hold boost pressure; relieve before removing clamps.
  • Hot CAC surfaces and EGR components cause burns during inspection.
  • Wear eye protection during boost leak soap tests.

When to Limp In vs Tow

Tow if derate leaves insufficient power for safe hill climbing or if white exhaust smoke and rapid coolant loss suggest a failed EGR cooler dumping coolant into the intake.

Prevention Tips for Fleets & Owner-Operators

  • Inspect CAC boots and clamps every oil change.
  • Replace EGR cooler O-rings and gaskets at recommended intervals.
  • Clean CAC exterior fins annually in dusty applications.

Related Fault Codes

SPN 105 FMI 3 — Intake Manifold Temperature Sensor

Voltage above normal on IMT circuit; electrical rather than real high temperature.

SPN 110 FMI 0 — Engine Coolant Temperature Sensor

Coolant overtemp often accompanies EGR cooler failures that also raise IMT.

SPN 102 FMI 16 — Boost Pressure

High boost pressure can correlate with charge-air heat issues on the same event.

Frequently Asked Questions

What does Mack SPN 105 FMI 16 mean?

Intake manifold 1 temperature is above normal with valid sensor data at moderately severe level.

Will high intake temp derate the engine?

Yes. Mack protection logic reduces torque to prevent turbo and engine damage from overheated intake charge.

Can a boost leak cause high IMT?

Yes. Leaks between the turbo and manifold reduce charge-air cooling effectiveness and raise temperature.

How do I test the IMT sensor?

Measure NTC resistance at known temperature; compare to Mack spec, typically 2.5-4.5k ohms at 77F.

Is EGR cooler failure common with this code?

It is a frequent cause when coolant loss and white smoke accompany the fault.

Can I clear the code after fixing a boot leak?

Yes, after repair verify IMT drops under load in ServiceMaxx, then clear and road test.

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