Powertrain Controls - ECM/PCM

DTC 23 Air Temp Sensor Diagnosis (CMFI) - Low Temp Indicated:

Intake Air Temp Circuit (CMFI) Wiring:

CIRCUIT DESCRIPTION:
The Intake Air Temperature (IAT) sensor is a thermistor that controls the signal voltage to the PCM. The PCM applies a voltage (4-6 volts) on CKT 472 to the sensor. When the air is cold, the sensor (thermistor) resistance is high, therefore, the PCM will see a high signal voltage. If the air is warm, the sensor resistance is low, therefore, the PCM will see a low voltage.

DTC 23 WILL SET WHEN:
^ A signal voltage indicates an Intake Air Temperature (IAT) below -38° C (-36° F) for 12 seconds.
^ Time since engine start is 4 minutes or longer.
^ No VSS (vehicle not moving).

ACTION TAKEN (PCM WILL DEFAULT TO):
The Malfunction Indicator Lamp (MIL) will illuminate.

DTC 23 WILL CLEAR WHEN:
Conditions for fault are no longer present and Tech 1 scan tool clear DTCs function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and ECM "B" fuse is removed for 10 seconds.

DTC CHART TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step will determine if DTC 23 is the result of a hard failure or an intermittent condition.
2. A DTC 23 will set, due to an open sensor, wire, or connection. This test will determine if the wiring and PCM are OK.
3. This will determine if the signal CKT 472 or the 5 volt return CKT 455 is open.

DIAGNOSTIC AIDS:
A Tech 1 scan tool reads temperature of the air entering the engine and should read close to ambient air temperature when engine is cold, and rises as underhood temperature increases.
Carefully check harness and connections for possible open CKT 472 or 455.
Refer to Diagnosis By Symptom/Intermittents - Intermittent Malfunctions
The "Temperature to Resistance Value" scale within the diagnostic chart may be used to test the IAT sensor at various temperature levels to evaluate the possibility of a "skewed" (mis-scaled) sensor. A "skewed" sensor could result in poor driveability complaints.