C: Intake Air Temperature (IAT) Sensor
Introduction
Introduction
1994 PCED OBDI-A | SECTION 18A: Diesel Diagnosis — 7.3L DI Engine |
C: Intake Air Temperature (IAT) Sensor Introduction | C: Pinpoint Tests |
The IAT (Intake Air Temperature) sensor is a thermistor-type sensor with a variable resistance that changes when exposed to different temperatures. When interfaced with the PCM, it produces a 0 to 5 volt analog signal that will measure temperature.
The IAT sensor's primary function is to measure ambient air temperature in order to determine when the exhaust back pressure device is needed.
An IAT signal that is detected out of range high or low by the PCM will cause the engine to ignore the IAT signal, disable exhaust back pressure operation and assume an ambient temperature of 59°F (15°C).
After removing connectors always check for damaged pins, corrosion, loose terminals, etc.
| Test Points | Spec. | Actual | Comments |
|---|---|---|---|
| B to Grd | <5 ohms | Resistance to ground, if greater than 5 ohms the harness is open. | |
| A to Grd | >5 ohms | Resistance less than 5 ohms indicates a short to ground. |
| Test Points | Spec. | Actual | Comments |
|---|---|---|---|
| B to Grd | 4.65-5 volts | Pull up voltage, if no or low voltage circuit has open or high resistance. | |
| A to Grd | 0-.25 volts | If greater than .25 volts signal wire is shorted to VREF or battery. |
| Test Points | Spec. | Actual | Comments |
|---|---|---|---|
| No. 39 to A | <5 ohms | Resistance from sensor connector to 104 pin connector. | |
| No. 19 to B | <5 ohms | Resistance from sensor connector to 104 pin connector. |
| k Ohms | IAT (Volts) | Degrees C | Degrees F |
|---|---|---|---|
| 1.19 | 0.28 | 120 | 248 |
| 1.56 | 0.36 | 110 | 230 |
| 2.08 | 0.47 | 100 | 212 |
| 2.80 | 0.61 | 90 | 194 |
| 3.84 | 0.80 | 80 | 176 |
| 5.34 | 1.04 | 70 | 158 |
| 7.55 | 1.34 | 60 | 140 |
| 10.93 | 1.72 | 50 | 122 |
| 16.11 | 2.15 | 40 | 104 |
| 24.25 | 2.63 | 30 | 86 |
| 37.34 | 3.09 | 20 | 68 |
| 58.99 | 3.52 | 10 | 50 |
152 = Signal voltage was greater than 4.59 volts for more than .20 seconds.
151 = Signal was less than .13 volts for more than .20 seconds.
| C: Pinpoint Tests |