Powertrain Controls - ECM/PCM

DTC 48 Intake Air Temperature (IAT) Circuit High (Low Temperature Indicated):

Intake Air Temperature (IAT) Circuit High (Low Temperature Indicated):

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor is a thermistor that controls signal voltage to the Powertrain Control Module (PCM). When the air is cold, the sensor resistance is high, therefore the PCM will see high signal voltage. As air warms, sensor resistance becomes less and voltage drops.

DIAGNOSTIC TROUBLE CODE (DTC) 48 WILL SET WHEN
Intake air temperature less than -38°C (-39°F) for 2 minutes.

ACTION TAKEN (PCM will default to)
Possible poor performance during cold weather operation.

DTC 48 WILL CLEAR WHEN
The fault condition(s) no longer exist.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
. This step determines if DTC 48 is a hard failure or an intermittent condition.
2. This test will determine if circuit 472 is shorted to ground.
3. This step will determine if there is a wiring problem or a faulty PCM.

DIAGNOSTIC AIDS
Check harness routing for a potential short to ground in CKT 472.
Tech I scan tool displays intake air temperature in degrees centigrade. A faulty connection or an open in CKTs 472 and 452 will result in a DTC 14.
If DTC 33 is intermittent, refer to Intermittents. - Intermittent Malfunctions
The "Temperature to Resistance Value" scale may be used to test the engine coolant sensor at various temperature levels to evaluate the possibility of a "skewed" (mis-scaled) sensor. A "skewed" sensor could result in poor driveability complaints.