Part 1 of 2
CODE 23 MANIFOLD AIR TEMPERATURE (MAT) SENSOR CIRCUITCode Chart 23 (Part 1 Of 2):
IAT Sensor Circuit:
CIRCUIT DESCRIPTION:
The Intake Air Temperature (IAT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage (4-6V) on BLU/BLK wire to the sensor. When manifold air is cold, the sensor (thermistor) resistance is high, therefore, the ECM will see a high signal voltage. As the air warms, the sensor resistance becomes less, and the voltage drops.
TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.
1. This step checks to see if Code 23 is the result of a hard failure or an intermittent condition. A Code 23 will set if:
a. Engine has been running for longer than 2 minutes.
b. Signal voltage indicates an IAT temperature less than -30°C.
2. This test simulates conditions for a Code 23 (High Temperature Indicated). If the Scan tool displays a high temperature, the ECM and wiring are OK.
3. This step checks continuity of BLU/BLK wire and BLK/WHT wire. If BLK/WHT wire is open, there may also be a Code 21.
DIAGNOSTIC AIDS:
If the engine has been allowed to cool to an ambient temperature (overnight), coolant and IAT temperatures may be checked with a Scan tool and should read close to each other. A Code 23 will result if BLU/BLK wire or BLK/WHT wire become open. If Code 23 is intermittent, Testing and Inspection