DTC 23

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

Wiring Diagram for Manifold Air Temperature Sensor Circuit.:

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.
1. Code 23 will set if:
A signal voltage indicates a manifold air temperature below -30C (-22 degrees F) for 12 seconds.
Time since engine start is 4 minutes or longer
No Vehicle Speed Sensor (VSS) vehicle not moving

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. The MAT sensor is difficult to reach and this test can be performed by disconnecting the MAT jumper harness connector. If the "Scan" indicates a temperature of over 130C, the jumper harness to the sensor should be checked before replacing the sensor.


3. This will determine if the signal CKT 472 or the sensor ground (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 increases. Carefully check harness and connections for possible open CKT 472 or 452, Refer to "Intermittents" in DIAGNOSIS BY SYMPTOM - NO TROUBLE CODE STORED.