Powertrain Controls - ECM/PCM

Code 23 Diagnostic Chart:

Intake Air Temperature (IAT) Sensor Wiring Schematic:

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor uses a thermistor to control the signal voltage at the Powertrain Control Module (PCM). The PCM applies a voltage (about 5 volts) on CKT 472 to the sensor. When the air is cold the sensor (thermistor) resistance is high, therefore the PCM terminal "PC9" voltage will be high. If the air is warm, the sensor resistance is low, therefore PCM terminal "PC9" voltage will be low.

DTC 23 WILL SET WHEN
^ A signal voltage indicates a intake air temperature below about -40°C (-40°F).
^ Time since engine start is 320 seconds or longer.
^ Vehicle speed less than 15 mph.

ACTION TAKEN (PCM WILL DEFAULT TO)
Malfunction Indicator Lamp (MIL) illuminates. PCM will default to 60°C for intake air temperature.
NOTE: Tech 1 scan tool will not show defaulted value.

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step checks if DTC 23 was set as a result of a hard or 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 sensor ground CKT 469 is open.

DIAGNOSTIC AIDS
^ A Tech 1 scan tool displays temperature of the air entering the engine, which should be close to ambient air temperature when engine is cold, and rise as underhood temperature increases.
^ A faulty connection, or an open in CKT 472 or CKT 469 can result in a DTC 23.
^ DTCs 23 and 34 stored at the same time, could be the result of an open CKT 469.
^ The "Temperature vs. Resistance Values" scale, in the diagnostic chart, may be used to test the IAT sensor at various temperatures to evaluate the possibility of a "skewed" (mis-scaled) sensor. A "skewed" sensor could result in poor driveability complaints.
^ Refer to "DIAGNOSIS BY SYMPTOM/INTERMITTENTS" Testing and Inspection