Code 23, IAT Sensor Circuit, Low Temperature Indicate: Notes

Intake Air Temperature (IAT) sensor uses a thermistor in series with a fixed resistor inside ECM to control signal voltage to ECM. ECM applies 5 volts to IAT sensor. ECM monitors voltage across IAT sensor and converts it into temperature reading. When outside temperature is cold, IAT resistance is high. When outside temperature is warm, IAT resistance is low. Therefore, when air temperature is cold, ECM will receive a high voltage input. When air temperature is warm, ECM will receive a low voltage input. Code 23 will set if voltage input at ECM indicates for 3 seconds that air temperature is less than -54°F (-48°C).

1. This test simulates Code 25. If ECM stores Code 25, ECM and its wiring are okay and IAT sensor is faulty. If Code 23 resets, IAT sensor is okay and wiring to ECM or ECM is faulty.
2. Checks for open in Gray or Light Green/Black wire, a short to B+ in Gray wire or a faulty ECM.