DTC 23

Code 23 Chart:

Code 23 Wiring Diagram:

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.

NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.


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

Code 23 will set if:

^ A signal voltage indicates manifold air temperature below -40~C (-40~F) for 4 seconds. Due to the conditions necessary to set a code 23, the "SERVICE ENGINE SOON" 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, replace the sensor.

DIAGNOSTIC AIDS:

^ A "Scan" tool reads temperature of the air entering the engine and should read close to ambient air temperature when engine is cold, and rise as underhood temperature increase.

^ Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS. If the engine has been allowed to sit overnight, the manifold air temperature and coolant temperature values should read within a few degrees of each other.