Powertrain Controls - ECM/PCM

Code 23 Chart:

Code 23 Wiring Diagram:

CIRCUIT DESCRIPTION:


The MAT sensor is a thermistor. 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 measure a high signal voltage. If the air is warm, the sensor resistance is low, therefore, the ECM will measure 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 signal voltage indicates a manifold air temperature below -40 C (-40 F) for 4 seconds. Due to the conditions necessary to set a Code 23, the "SEVICE 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, inspect the air cleaner assembly for the presence of ice. If OK, replace the sensor.