SPN Fault Codes Verified Factory Specs

SPN 105 FMI 3: Intake Manifold Temperature Sensor Circuit Open

Diagnostic trouble guide for SPN 105 FMI 3 (Intake Manifold Air Temperature Sensor High Voltage / Open Circuit). Resistance chart, thermistor cleaning, and fan lock-on diagnosis.

SPN 105 FMI 3 Moderate (EGR System Restricted)

System Overview: Air Intake / Charge Air Cooler (CAC)

Intake manifold air temperature sensor signal voltage exceeded 4.90V, indicating open circuit or failed thermistor.

Driver Symptoms

Engine fan locked on high speed continuously
EGR valve operation disabled to prevent thermal runaway
Mild fuel economy loss (1-2 MPG)

Probable Causes

Oil/soot soaked intake temperature thermistor element in intake elbow
Broken wire in overhead engine sensor harness
Sensor internal thermistor failure

Diagnostic Steps

Remove sensor from intake manifold intake runner; inspect for thick carbon/EGR sludge and clean with non-chlorinated brake cleaner
Measure sensor resistance at room temperature (77°F / 25°C): should read approximately 2.0k to 3.0k Ohms
Check 5V reference supply on Pin 1 with Key ON

Sensor Wiring Pinout: 2-Pin Weatherpack: Pin 1 (+5V DC Reference), Pin 2 (Signal to ECM Pin 28)