DTC 23

Chart - Code 23 Manifold Air Temperature (Signal Voltage High):

Wiring Diagram for Manifold Air Temperature Sensor.:

CODE 23 - MANIFOLD AIR TEMPERATURE (MAT) SENSOR CIRCUIT (LOW TEMPERATURE INDICATED)



Circuit Description:
The Manifold Air Temperature (MAT) sensor uses a thermistor to control the signal voltage to the Electronic Control Module (ECM). The ECM 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 ECM will see a high signal voltage. If the air is warm the sensor resistance is low, therefore, the ECM will see a low voltage.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.
Code 23 will set if a signal voltage indicates a manifold air temperature below -40 Degrees C (-40 Degrees F) for 4 seconds.
Due to the conditions necessary to set a Code 23, the "Service Engine Soon" (SES) light will only stay "ON" while the fault is present.


1. A "Scan" tool may not be used to diagnose this fault, due to the ECM transmitting "default" (substitute) values, when the fault is present. A Code 23 will set, due to an open sensor, wire, or connection. This test determines if the wiring and ECM are OK.
2. If the resistance is greater than 25,000 ohms check the air cleaner assembly for ice, if none present, replace the sensor.