SPN 105 FMI 3 indicates the intake manifold temperature sensor circuit voltage is above the normal maximum — an open circuit or high-signal class fault. Open signal wire, failed thermistor, unplugged connector after intake service, corroded terminals, and reference or ground anomalies are the primary causes. An open IAT circuit typically reports an extreme cold value that skews fueling density calculations and boost strategy.

Inspect the IAT sensor connector at the intake plumbing. Check for chafe near brackets and moisture in the connector body after wash events. Confirm connector is fully locked after any recent intake or air filter service.

Confirm 5V reference, ground, and signal at the IAT sensor connector. A cold-soak reading should approximate ambient temperature once the circuit is healthy. An open circuit often reads an extreme cold value — this is a circuit fault, not a true temperature reading. Resistance versus temperature charts are available from OEM service data for thermistor verification.