Circuit Test IAT - Intake Air Temperature Sensor

WARNING: This page is about a different car, the 1994 Mercury Tracer and 1994 Ford Escort. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: IAT Sensor Circuit & Connector Terminal ID (IAT - 1.8L)

NOTE: Enter this test only when a Code 10 is displayed during self-test procedures (KOEO or KOER) or when directed here from another circuit test. This test is intended to diagnose IAT circuit only.

CIRCUIT PIN IDENTIFICATION

Circuit	Breakout Box Pin No.	PCM Pin	Wire Color
A/T
IAT	25	2K	Red/Black
SIG RTN	46	3D	Black/White
M/T
IAT	45	2P	Red/Black
SIG RTN	46 & 49	2D	Black/White

1) Check System Integrity Visually check all wiring, connectors and components for evidence of damage, shorting or looseness. If a fault is found, repair as necessary. If no fault is found, go to next step.

2) Check IAT Resistance Turn ignition off. Install breakout box, leaving PCM disconnected. Access IAT sensor. Sensor is located in Volume Airflow (VAF) meter. Monitor temperature at IAT sensor using Rotunda Digital Thermometer (055-00100). Measure resistance between IAT and SIG RTN test pins at breakout box. Heat sensor using heat gun. Compare readings with RESISTANCE SPECIFICATIONS (IAT SENSOR) table. If resistance is not as specified, go to next step. If resistance is as specified, IAT circuit is okay. If no other problem or code is found, replace PCM.

RESISTANCE SPECIFICATIONS

Temperature °F (°C)	Ohms
32 (0)	4000-7000
68 (20)	2000-3000
104 (40)	900-1300
140 (60)	400-700

3) Check For Open IAT Wire Ensure ignition is off, breakout box is installed and PCM is disconnected. Disconnect VAF sensor connector. Measure resistance between IAT test pin at breakout box and IAT terminal at VAF or MC-VAF sensor connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open IAT wire.

4) Check For Short In IAT Wire Ensure ignition is off, breakout box is installed and PCM is disconnected. Disconnect VAF sensor connector. Measure resistance between ground and IAT test pin at breakout box. If resistance is more than 10,000 ohms.

5) Check IAT Sensor SIG RTN Ensure ignition is off. Ensure breakout box is installed (PCM disconnected) and VAF sensor is disconnected. Measure resistance between SIG RTN test pin at breakout box and SIG RTN terminal at VAF sensor connector. If resistance is 5 ohms or more, repair IAT sensor SIG RTN wire. If resistance is less than 5 ohms, replace VAF sensor.