Powertrain Controls - ECM/PCM

Diagnostic Trouble Code (DTC) 23:

Intake Air Temperature Sensor Circuit:

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor uses a thermistor to control the signal voltage to the Powertrain Control Module (PCM). The PCM applies a voltage (about 5 volts) on CKT 472 to the sensor. When the intake air is cold, the sensor (thermistor) resistance is high, therefore, the PCM will sense a high signal voltage. If the intake air is warm, the sensor (thermistor) resistance is low, therefore, the PCM will sense a low voltage.

DIAGNOSTIC TROUBLE CODE (DTC) 23 WILL SET WHEN
IAT signal voltage indicates an intake air temperature below 35°C (-31°F), Engine Coolant Temperature (ECT) above 85°C (185°F), engine idling, no Vehicle Speed Sensor (VSS) and all conditions met for 60 seconds or IAT signal voltage indicates an intake air temperature below -35°C (-31°F), DTC 14 or 15 present, engine idling, no VSS and all conditions met for 7 minutes.

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

DTC CHART TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Monitoring IAT with a Tech 1 scanner will determine if the fault is 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 IAT sensor signal (CKT 472) or the IAT sensor ground (CKT 452) is open.

DIAGNOSTIC AIDS
The scan tool displays temperature of the air entering the engine and should display close to ambient air temperature when engine is cold, and rise as underhood temperature increases.

Carefully check harness and connections for possible open.

If DTC 21, or 66 are also set, check CKT 452 for being open or faulty PCM connection.

Refer to Diagnosis By Symptom/Intermittents. - Intermittent Malfunctions

If the engine has been allowed to sit overnight, the intake air temperature and engine coolant temperature values should display within a few degrees of each other.