IAT Sensor (Intake Air Temperature)
Location, connector pinout, test procedure, and related fault codes for the intake air temperature sensor on Class 8 diesel trucks.
Last updated: 2026-09-20
Overview
The IAT (Intake Air Temperature) sensor measures the temperature of air entering the intake manifold. The ECM uses this reading to adjust fuel delivery, EGR flow, and cold-start strategies. A failed IAT sensor can cause hard starts in cold weather, excessive smoke, or derate conditions.
Sensor Locations by Platform
Cummins X15
Intake manifold — driver side, threaded into manifold. Often near or combined with MAP sensor on some X15 configurations.
Some X15 configurations use a combined MAP/IAT sensor in a single housing.
PACCAR MX-13
Intake manifold — driver side. Threaded into manifold near rear of engine.
MX-13 IAT sensor is a separate 2-wire sensor, not combined with MAP.
Detroit DD15
Intake manifold — driver side, near EGR inlet. Threaded into manifold.
DD15 IAT sensor is accessible from the driver side with minimal disassembly.
Volvo/Mack MP8
Intake manifold — passenger side. Some MP8 applications combine IAT with MAP sensor.
Verify whether your MP8 application uses a combined MAP/IAT or separate sensors.
DieselVision™ identifies sensor labels and connector pin numbers — upload a close-up photo and the system maps pins automatically.
Connector Pinout
| Pin | Function | Specification |
|---|---|---|
| A | Signal (Temperature) | High resistance (cold) to low resistance (hot). ~2.5V at 25°C, drops as temp rises |
| B | Ground (Signal Return) | <0.1V to chassis ground |
Test Procedure
Read IAT sensor temperature in live data before engine start
Expected: Should match ambient air temperature. If reading -40°C or 125°C = open or short circuit
Tool: OEM diagnostic software
Measure sensor resistance across pins A and B (sensor disconnected, key off)
Expected: At 25°C: ~2,000–3,000 ohms. Resistance decreases as temperature increases. Infinite resistance = open circuit
Tool: Multimeter (ohms)
Measure ground circuit resistance from pin B to chassis ground
Expected: <0.5 ohms
Tool: Multimeter
Check signal wire for short to ground (sensor disconnected, key off)
Expected: >1 MΩ between pin A and chassis ground
Tool: Multimeter
Apply heat to sensor body and monitor resistance change
Expected: Resistance should decrease smoothly as temperature increases. Erratic change = failing sensor
Tool: Heat gun + Multimeter
Common Failure Modes
- •Open circuit — sensor reads -40°C (minimum value)
- •Short to ground — sensor reads maximum temperature
- •Internal thermistor failure — stuck reading
- •Connector corrosion causing high resistance
- •Sensor contamination from oil mist in intake
Frequently Asked Questions
Where is the IAT sensor located on a diesel engine?
The IAT sensor is threaded into the intake manifold. On most Class 8 platforms it is on the driver side of the engine, near the EGR inlet or combined with the MAP sensor.
What does an IAT sensor reading of -40°C mean?
A reading of -40°C (the minimum value) typically indicates an open circuit in the sensor or signal wire. Check sensor resistance and wiring.
How do I test an IAT sensor?
Disconnect the sensor and measure resistance across the two pins. At room temperature (25°C) you should see approximately 2,000–3,000 ohms. Infinite resistance means the sensor is open.
What fault codes are caused by a failed IAT sensor?
Common fault codes include SPN 105 FMI 3 (voltage above normal / short to voltage) and SPN 105 FMI 4 (voltage below normal / open circuit or short to ground).
Snap a photo of your scan tool screen and let Diesel Vision interpret the fault instantly — no manual code lookup required.
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