DTC 23

Code 23 Chart:

Code 23 Wiring Diagram:

CIRCUIT DESCRIPTION:

The MAT sensor uses a thermistor to control the signal voltage to the 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.

1. Code 23 will set if:

^ A signal voltage indicates a manifold air temperature below -35~C (-31~F).
^ Time since engine start is 4 minutes or longer.
^ No VSS.

2. A Code 23 will set, due to an open sensor, wire, or connection. This test will determine if the wiring and ECM are OK.

3. This will determine if the signal CKT 472 or the 5 volts return CKT 452 is open.


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.

^ A faulty connection, or an open in CKT 472 or 452 will result in a Code 23.

^ Codes 23 and 34 stored at the same time, could be the result of an open CKT 452 which would also turn the temperature warning indicator "ON". CKT 452 is routed through a mini harness. A faulty connection could result in intermittent failures. The "Temperature to Resistance Values" scale may be used to test the MAT sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor. A "slewed" sensor could result in poor driveability complaints.

^ Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.