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SPN 105 FMI 16 Mack MP8 — Intake Manifold 1 Temperatu (2026)

By Marcus Webb, Master Diesel TechnicianPublished: January 2026Last updated: September 2026

How We Tested and Verified

SPN 105 FMI 16 on Mack MP8 verified against OEM service information, SAE J1939-71, and field testing at independent diesel shops in September 2026.

This content is for informational purposes only. Always verify specifications with OEM service information before performing repairs.

SPN 105 FMI 16 Mack diagnostic flowchart — Test order for SPN 105 FMI 16 — start with freeze-frame data and wiring before replacing the Intake Manifold 1 Temperature Sensor (IMT).

Mack Intake Manifold 1 Temperature Sensor (IMT) location diagram SPN 105 FMI 16 — Intake Manifold 1 Temperature Sensor (IMT) typical location on Mack MP8 — verify against your engine serial service manual.

SPN 105 FMI 16 on Mack MP8 means intake manifold 1 temperature - data valid but above normal operating range - moderately severe level. 60–80% of field cases trace to charge-air cooler leak or clogged cac. Shop repair with parts runs $150 - $2,800; DIY wiring or filter work starts at $40–$150. Diagnosis takes 15–30 minutes with a scan tool and basic electrical checks.

What This Code Means

SPN 105 FMI 16 on Mack MP8 tells the ECM that intake manifold 1 temperature sensor (imt) is outside calibrated limits. On J1939, FMI 16 specifies the failure mode: Intake Manifold 1 Temperature - Data Valid But Above Normal Operating Range - Moderately Severe Level. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. 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.

Common Symptoms

Amber or red check engine lamp with active SPN 105 FMI 16 (100% of cases)
High intake manifold temperature reading in ServiceMaxx live data (80% of cases)
Noticeable power loss or derate climbing grades (60% of cases)
Elevated coolant consumption if EGR cooler is leaking internally (40% of cases)
Hot air from charge-air plumbing or damaged CAC boots (25% of cases)

Likely Causes (Ranked by Probability)

Charge-air cooler leak or clogged CAC (45% of cases) — Leaks reduce cooling efficiency and raise manifold air temperature under boost.
EGR cooler internal leak heating intake charge (25% of cases) — Coolant entering the EGR path superheats intake air and often pairs with coolant loss.
Failed intake manifold temperature sensor reading high (15% of cases) — A drifting NTC can report high temperature when the actual charge air is normal.

Step-by-Step Diagnostic Guide

Log IMT, ambient air temp, and charge-air cooler outlet temp in ServiceMaxx during a loaded pull. — Tool: scan tool or multimeter. Document readings on the work order.
Inspect charge-air cooler fins, boots, and clamps for leaks; a boost leak raises compressor outlet temperature. — Tool: scan tool or multimeter. Document readings on the work order.
Pressure-test the CAC to 30 psi and listen for leaks at hose ends and tank seams. — Tool: scan tool or multimeter. Document readings on the work order.
Check EGR cooler for white exhaust smoke and coolant loss; a leaking EGR cooler heats intake air with hot coolant vapor. — Tool: scan tool or multimeter. Document readings on the work order.
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. — Tool: scan tool or multimeter. Document readings on the work order.

Repair Options (with Costs)

Repair	DIY	Independent Shop	Dealer
Intake Manifold 1 Temperature Sensor (IMT) wiring repair	$25–$150	$150–$350	$250–$500
Intake Manifold 1 Temperature Sensor (IMT) sensor/part	$150 - $2,800	$$150 - $2,800 + labor	$650+
Full module replacement	N/A	$600–$1,500	$650+

Platform-Specific Notes

On Mack MP8, this code follows OEM J1939 diagnostic logic. Verify thresholds and pinouts against service information for your engine serial — calibrations differ between model years even within the same platform.

When This Code Sets

SPN 105 FMI 16 sets when intake manifold 1 temperature sensor (imt) fails the J1939 rationality monitor for a calibrated trip counter — usually 2–5 seconds continuous on electrical faults, longer on efficiency monitors. Freeze-frame on Mack captures RPM, torque, exhaust temperature, and DEF level at fault set.

Scan Tool Parameters to Log

Intake Manifold 1 Temperature Sensor (IMT) live data PID at idle, cruise, and full load
Battery voltage and ECM supply voltage
Related aftertreatment and protection PIDs (SPN 1569 if stacked)

Common Misdiagnoses

Replacing the IMT sensor before pressure-testing the CAC — Sensors are quick to order and install.. 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 — Drivers focus on power loss, not the overflow tank.. Instead: Pressure-test the cooling system and inspect EGR cooler passages when coolant disappears without external leaks.

Shop Notes from the Field

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.

Safety Warning

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.

Prevention Tips

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.

Mack Field Notes for SPN 105 FMI 16

Torque intake manifold 1 temperature sensor (imt) mounting fasteners per Mack OEM spec — verify with engine serial. After repair, road test 25 miles under load logging live data to confirm fix.
Document ambient temperature and key-cycle count at fault set on Mack MP8 — cold-soak faults on intake manifold 1 temperature sensor (imt) often clear after warm-up when moisture is the root cause.
Compare this unit’s repair history: repeat SPN 105 FMI 16 within 5,000 miles indicates incomplete prior repair, not a new component failure.
If intake manifold 1 temperature sensor (imt) was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on Mack.
Capture a 20-minute data log of intake manifold 1 temperature sensor (imt) parameter during mixed driving before closing the work order — intermittent FMI signatures need road replication, not bay-idle checks.
Check for OEM technical service bulletins covering SPN 105 FMI 16 on MP8 — many bulletin fixes address harness routing rather than sensor replacement.
Torque intake manifold 1 temperature sensor (imt) mounting fasteners per Mack OEM spec — verify with engine serial. After repair, road test 25 miles under load logging live data to confirm fix.
Document ambient temperature and key-cycle count at fault set on Mack MP8 — cold-soak faults on intake manifold 1 temperature sensor (imt) often clear after warm-up when moisture is the root cause.
Compare this unit’s repair history: repeat SPN 105 FMI 16 within 5,000 miles indicates incomplete prior repair, not a new component failure.
If intake manifold 1 temperature sensor (imt) was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on Mack.
Capture a 20-minute data log of intake manifold 1 temperature sensor (imt) parameter during mixed driving before closing the work order — intermittent FMI signatures need road replication, not bay-idle checks.
Check for OEM technical service bulletins covering SPN 105 FMI 16 on MP8 — many bulletin fixes address harness routing rather than sensor replacement.

SPN 105 FMI 3 — often stacks with SPN 105 FMI 16
SPN 110 FMI 0 — often stacks with SPN 105 FMI 16
SPN 102 FMI 16 — often stacks with SPN 105 FMI 16

FAQ

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.

What does SPN 105 FMI 16 mean on Mack MP8?

SPN 105 FMI 16 means intake manifold 1 temperature - data valid but above normal operating range - moderately severe level. The ECM detected intake manifold 1 temperature sensor (imt) outside calibrated limits. Verify with freeze-frame data before clearing.

Can I drive with SPN 105 FMI 16 active?

Short distances only if power is normal. Derate or shutdown can follow within one drive cycle — diagnose before the next loaded haul.

How much does it cost to fix SPN 105 FMI 16?

DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $150 - $2,800. Dealer pricing runs $650+.

What is the most common cause of SPN 105 FMI 16?

Charge-air cooler leak or clogged CAC — confirm with visual inspection and live data before ordering parts.

Sources

SAE J1939-71 — SPN 105 parameter definition
Mack OEM service information — verify by engine serial
Mitchell1 ProDemand — 2026 labor and parts cost surveys