Powertrain Controls - ECM/PCM

DTC 38 Chart:

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor is a thermistor. The PCM applies a voltage (about 5 volts) on CKT 472 to the sensor. When the air is cold, the sensor resistance is high and the PCM will measure a high signal voltage. If the air is warm, the sensor resistance is low causing the PCM to measure a low voltage. If the IAT sensor indicates too low of a temperature, the PCM will set DTC 38.

DTC 38 WILL SET WHEN
- DTC 135 is not set.
- 7 mph or greater for 5 seconds.
- Outside air temperature sensor is not failed.
- Outside air temperature is -10°C (14°F) or greater, or outside air temperature is 17°C (62°F) greater than IAT.
- IAT sensor signal indicates temperature of-37°C (-34°F) or less.

ACTION TAKEN (PCM WILL DEFAULT TO)
The PCM will illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon) lamp and substitute the outside air temperature sensor value for the IAT value.

DTC 38 WILL CLEAR WHEN
The fault no longer exists.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Checks for current fault condition.
2. Checks the integrity of the IAT circuit and the PCM.
3. Isolates the signal circuit from the ground circuit.

DIAGNOSTIC AIDS
- If the engine has been allowed to cool to an ambient temperature (overnight), engine coolant and intake air temperatures may be checked with a scan tool and should read about the same.
- It DTC 38 is intermittent or a "Hard Start" symptom is present, check intake air temperature with a scan tool on a cool engine. Temperature should display within 5° of the ambient.